Radio Shack Stock Options

Site dos EUA - Sem cookies - Sem spyware - Sem adware - Sem trojans - Sem vírus - Sem worms - Sem spam - Sem pop-ups Respeitamos a sua privacidade - NÃO monitoramos suas compras nem controlamos você em linha, nem compartilhe seus dados ABQ Techzonics Earthshaking Online Tech Superstore Consideramos seriamente todas as melhores ofertas razoáveis, negociações de preços, ofertas de comércio. Somos o seu perfeito super ponto de compras para preencher suas listas de peças de alta tecnologia. ELETRÔNICA COLECTIVA: ELETRÔNICA ANTIGA, ELETRÔNICA DE VINTAGE, ELETRÔNICA RARA, ELETRÔNICA DE OURO SEU LOJA DE COLECCIÍLIOS OFICIAIS ONLINE: 100s de Coleções Eletrônicas Collectibles Eletrônicas e Coleções Eletrônicas, incluindo eletrônicos raros (especialmente eletrônicos vintage raros e eletrônicos antigos), eletrônicos banhados a ouro (Gold Electronic Parts Gold Electronic Components), Transistores de germânio e Tetrodes, eletrônicos eletrônicos colecionáveis Equipamento e ferramentas eletrônicas, materiais eletrônicos de coleção - Vintage, Antique, Steampunk, retro, anacrônico, histórico, Antiquário Listado abaixo é apenas nosso equipamento de teste eletrônico Collectible Electronic Parts Collectible - Nós também vendemos 1.000 de outras peças eletrônicas e equipamentos eletrônicos (consulte o SITEMAP para links de páginas da Web) Para nossas máquinas e ferramentas coletivas, veja a página de Colecionadores-Máquinas-Ferramentas para todos os outros Colecionáveis, veja nossa página de Colecionadores-Arte-Artesanato-Vários SUA TINTA DE COMPRAS ONLINE ONE-STOP ONLINE VER NOSSAS páginas da SUPERSTORE PARA: COMPONENTES ELÉCTRICOS COMPONENTES ELÉCTRICOS. Circuitos integrados (circuitos integrados), transistores, diodos, retificadores, LEDs, capacitores, resistências, potenciômetros (potes), varistores, indutores, bobinas, transformadores, falantes, relés, interruptores, atuadores, fusíveis, disjuntores, cristais, osciladores, conectores, Cabeçotes, soquetes, pinos, fios, cabos, expositores, fotos, vídeo, laser, energia, outras peças eletrônicas componentes eletrônicos. EQUIPAMENTO. Equipamento de teste eletrônico, equipamentos elétricos, computadores, periféricos, ferramentas elétricas, ferramentas manuais, cofres de ferramentas, veículos (carros, caminhões, motos). MORE TECH STUFF. ScientificIndustrial Válvulas, Conexões, Segurança Pessoal, Sobrevivência (Survivalists Preppers), Radionics, Artesanato, Passatempos, Strange amp Insólito, Religioso amplificador Espiritual, Colecionadores - Hardware, Dispositivos, Peças, Materiais Especiais, Livros, Manuais, Software Contato: wizguruconsumertronics. net Voz : 505-321-1034 (9-5 MST, MF) Envie um email para todas as encomendas, perguntas e perguntas Copyright copy 2008-2017, Consumertronics. Todos os direitos reservados PESQUISAR PARA ARTIGOS: Os itens são criados nesta página, principalmente com base na ordem nos obtemos. Use a caixa de pesquisa de topo direto ou o recurso Localizar busca do navegador para localizar os itens específicos de interesse ou simplesmente navegar na página da Web. Nós enumeramos muitos itens por mais de um nome e variação de nome (por exemplo, transistor quotgermanium, quotvintage linear transistorsquot). Se você não conseguir achar item na página, tente por outras variações de nome e, em seguida, por função e variações funcionais comumente conhecidas por (por exemplo, transistorsquot quotmusic), então procure nossas outras páginas de internet prováveis, veja SITEMAP para links. Se você precisa de peças eletrônicas ou equipamentos eletrônicos para uma função atual, também experimente nossos transistores regulares, vários circuitos integrados e outras páginas eletrônicas de peças. CONDIÇÕES DE ARTIGO: Salvo indicação em contrário, todos os itens descritos nesta página são novos estoque antigo (NOS) e nunca utilizados. Muitas vezes, compramos e trocamos peças novas, equipamentos e outros itens dos tipos aqui descritos, de preferência em quantidades maiores, algumas que reservamos para nossos próprios usos e coleções e outros inventários e alguns revemos aqui. Se você tiver itens para vender ou negociar desses tipos, entre em contato por e-mail. Todas as pequenas peças e materiais que adquirimos para revenda aqui devem ser novos, mas geralmente compramos e negociamos colecionáveis ​​e coleções usadas em boas condições, que descrevemos como quotusedquot para aqueles que revendemos. Por favor, envie um e-mail para nós (por favor, não ligue, como é frequente nos nossos laboratórios), use o e-mail Assunto: quotBuySellTrade Inquérito. QUOTAS DESCRIÇÕES amplificador IMAGENS: Ao contrário de muitas lojas on-line, nosso objetivo é sempre fornecer e limpar e corrigir imagens de itens e precisa e razoavelmente Complete as descrições dos itens. Embora tenhamos tentado ser 100 precisos em nossas descrições e imagens, informe-nos sobre quaisquer erros ou omissões aqui, por exemplo, enviando-nos URLs para as fichas de dados relevantes. Embora as imagens geralmente ajudem, a maioria dos itens que vendemos já são bem conhecidos. Se alguma das nossas descrições ou imagens estiverem faltando, incompletas ou imprecisas e isso afeta sua decisão de compra, envie-nos um e-mail (por favor, não coloque o quotNew Better Info para Itemquot na linha do assunto do email) para que possamos fazer correções razoáveis. Muitas de nossas imagens de hardware elétrico e eletrônico não mostram todos os cabos ou cabos que os itens atuais têm para que possamos fornecer imagens maiores e mais claras do corpo dos itens para melhor mostrar números de peças, rotulagem, características e condições cosméticas . OUTROS TIPOS DE MATERIAIS DE PEÇAS DE EQUIPAMENTO: Oferecemos dezenas de principais tipos de peças, equipamentos, hardware, materiais, colecionáveis ​​- você o nomeia. Acesse a página da loja apropriada da nossa para preencher suas necessidades. Combinado SH (veja abaixo) pode economizar muito dinheiro. Agora somos uma grande loja de departamento online. POLÍTICAS. A menos que seja explicitamente estabelecido o contrário nesta página, todas as políticas aplicáveis ​​são encontradas em: consumertronics. netpolicies. htm. PAGAMENTOS. Aceitamos cheques, ordens de pagamento, PayPal (PP), pagamento do serviço de transferência de dinheiro (MTS), comércio e dinheiro. Basta enviar-nos um e-mail (wizguru), uma lista do que deseja (Título, nome ou parte de cada escolha), incluir os preços com SH e seu nome, endereço de entrega e método de pagamento preferido, ou usar um dos nossos Formulários de Pedidos Online da Consumertronics. Nós enviamos dentro de 2 dias úteis após o período total de apuramento do pagamento desde o dia do depósito. Todos os pagamentos devem ser feitos nos EUA - sem dólares canadenses ou dólares australianos. Detalhes abaixo: (1) TRANSPORTE MAIS RÁPIDO. O pedido de pagamento postal dos Estados Unidos (PMO), o PMO canadense (fabricado nos EUA), o PP, o MTS e o caixa são considerados iguais em dinheiro por nós - o período de devolução é zero dias. Nota: Nós não somos responsáveis ​​pelo dinheiro enviado nos e-mails, então esconda bem. (2) MOs amp CHECKS DETAILS. Pague para: quot Consumertronics quot. TODOS OS VERMELHOS DE AMPLOS MOZ NON-PMO. Período de apuramento: 10 dias se 20-100, 20 dias se 101-250, 30 dias se for superior a 250. (3) DETALHES DOS SERVIÇOS DE TRANFER DO DINHEIRO (MTS). Pague para: quot John J. Williams (devido ao fato de que usar o MTS para pagar um nome de empresa geralmente é um incômodo maior). Todos os pagamentos de MTS acima de 500 exigem aprovação escrita por nós. Enquanto quase todos os MTS chegam aqui dentro de uma hora, alguns podem demorar alguns dias. (4) DETALHES DO PAGAMENTO. Vá para o PayPal. Faça um PP envie dinheiro para: quot wizguruconsumertronics. net quot. PP sobre 50 requer aprovação prévia, explícita e por escrito por nós por e-mail, e os pagadores de PP devem ser usuários de PP verificados, cuja transação PP deve fornecer proteção para vendedores. Para os compradores verificáveis ​​e repetidos, a ABQ Techzonics pode aumentar consideravelmente o limite de PP, caso em que ele envia um e-mail ao comprador no seu novo nível de PP. (5) ITENS PARA DETALHES COMERCIAIS. Quem não quer economizar dinheiro nos dias de hoje. Aceitamos itens de comércio. Ao fazer itens para comércio, você economiza dinheiro e se livra de um bom Item (s) que você precisa de menos do que Itens que oferecemos. A autorização prévia e explícita de nós é necessária antes de enviar para nós qualquer item para troca. Se estiver interessado, envie-nos um e-mail (wizguru. Coloque no email Assunto: quotItem for TradeInquiry. quot) com detalhes completos sobre o que você tem para oferecer e o que deseja (você deve possuir a exclusiva e exclusiva propriedade de todos os itens que você oferece para Nós para o comércio). Inclua a descrição completa de todos os itens, incluindo números de modelo e modelo, condições, quantidades, defeitos. NÃO nos telefone sobre itens de comércio. Se estiver interessado, enviaremos você de volta com aceitação condicional ou uma contra-oferta. Se os resultados de aceitação mútua, nós enviaremos por e-mail nossa permissão para enviar os Itens, o que você faz na sua despesa SH. Uma vez que seus itens de comércio chegam aqui, examinaremos eles, o que normalmente leva de 3 a 20 dias. Se aceitável para nós, enviaremos (a nossa despesa SH dentro de 2 dias úteis) o que nós concordamos em trocar com você. Nota: Não queremos TVs antigas, videocassetes, sistemas domésticos, computadores, monitores ou periféricos ou itens grandes e pesados, e todos os itens devem ser limpos e seguros para serem enviados e manipulados. Novamente, não envie nada até que você receba nossa aprovação explícita por escrito para fazê-lo. (6) PAGAR MONTANTE COMPLETO EXACTO. Por favor, pague o montante total exato da sua compra SH (envie-nos um e-mail se não tiver certeza). Se você pagar demais em mais de 5 ou 100 (o que for menor), reserve 90-120 dias para reembolsarmos a diferença. (7) TIPOS DE ORDEM INACEPTATIVOS. Não há cartões de crédito, devoluções, pagamentos parciais, pagamentos pós-pagos, quoton aprobationsquot ou qualquer outro tipo de pagamentos ou embarque não explicitamente aprovado aqui ou por nós, por escrito, antes do pagamento. Além disso, nos reservamos o direito de recusar qualquer pedido, forma de pagamento ou condições de venda ou de envio impostas pelo comprador sem responsabilidade para nós. Para nossos bons compradores: somos mais flexíveis nos tipos de pagamentos e condições de transporte. COMPRADORES ESTRANGEIROS. Alguns itens podem ser restringidos por regulamentos governamentais para exportação, e os Compradores assumem toda a responsabilidade pela legalidade de nossos embarques para eles e suas compras, bens e usos dos itens que enviamos para eles. PREÇO. Somos flexíveis em nossos preços e SH - especialmente para nossos bons clientes e para encomendas de quantidade e multi-itens - queremos ser justos para você e para nós. Os preços estão listados abaixo Descrição do item. Determinamos o preço do item com base nos preços de itens similares encontrados on-line e nas lojas. Nos casos de nenhum consenso claro de preços on-line ou de lojas, outras fontes foram usadas. Se nosso preço for muito alto para qualquer item que vendamos, consideraremos seriamente reduzir o preço - especialmente se você documentar que outros estão vendendo esse mesmo item ou item equivalente a preços mais baixos na quantidade que você precisa - nosso objetivo é vencer nossos concorrentes. Muitos itens, não estamos limitados às quantidades mostradas - se você precisar de mais e temos o que você precisa disponível, consideraremos seriamente sua oferta. Ao comprar um item em quantidade e ou mais de um item, você reduz muito seus custos SH por unidade. Na maioria dos casos, também podemos fazer menos quantidade se a sua ordem total for 10 (SH) e o preço médio de seus itens é de 5 cada. Basta enviar-nos um e-mail com suas necessidades, suas contra-ofertas e itens que deseja negociar. DESCONTOS ESPECIAIS. Até, 20, você pode tirar o preço de todos e todos os itens descritos nesta página na qual a palavra quotFirmquot não aparece ao lado do preço. OFERTAS ESPECIAIS DE QUANTIDADE O SALVE DE DINHEIRO. As vendas de quantidade maior (e de itens múltiplos e de entrega e entrega local) quase sempre resultam em poupança por item unit-plus-SH para VOCÊ. Temos alguns itens em quantidades muito maiores do que o oferecido acima, como geralmente indicado na descrição do item. Sim, se tivermos a quantidade para satisfazer as suas maiores necessidades de quantidade, consideraremos seriamente qualquer oferta razoável e mutuamente justa que você proporá, o que não só obterá a quantidade que você precisa, mas em uma economia substancial em você por preço unitário e por unidade SH custos (quantidade uniformemente divisível por 10 ou 25). Consideraremos seriamente a minimização de todos os outros vendedores principais dos mesmos itens. TRANSPORTE amplificador MANUSEAMENTO. Onde SH é indicado, é indicado para CONTINENTAL USA ORDERS. O envio de parte da SH é baseado em taxas reais de envio. Onde SH não está indicado, as seguintes cobranças SH aplicam-se: CONTINENTAL USA ORDERS. 5.90. ORDENS NON CONTINENTES DOS ESTADOS UNIDOS. 8.90. ORDENS ESTRANGEIRAS. Por favor, pergunte. O correio aéreo estrangeiro mínimo SH é 14.90 do Canadá e 22.90 todos os outros endereços estrangeiros, por isso, solicite o máximo possível para economizar SH estrangeiros substanciais. ARTIGOS MÚLTIPLOS LEVANTAM GRANDES CARTÕES. Nós somos o seu perfeito Super Store de compras únicas para peças de alta tecnologia para preencher suas listas de peças SH agora é caro e os carregadores estão constantemente aumentando suas taxas para poupar muito em SH, por favor, faça o pedido de tudo que você precisa hoje. Página da Web e todas as nossas outras páginas da web, pague todos eles em total em um pagamento para serem enviados todos juntos para o mesmo endereço. ALL USA amp CANADÁ ORDERS. Você paga o SH completo pelo seu item SH mais caro, mais metade SH para cada um dos outros itens que você compra. TODAS AS OUTRAS ORDENS ESTRANGEIRAS. Por favor, pergunte. MÉTODO DE ENVIO . Para os EUA, geralmente usamos o correio de prioridade ou o correio de mídia (se livro ou manual) se o frete de transporte for inferior a 75 da SH acima. Todos os freteiros estrangeiros são enviados por correio aéreo. Outras formas de envio dos EUA, incluindo UPS, FedEx, Overnight, Second Day Air, Segurados, etc. geralmente são OK, mas o SH será maior. Não iremos cobrar o frete à conta do comprador do comprador. EMBALAGEM ANTISTATICA. Todos os itens que são sensíveis eletrostaticamente (por exemplo, CMOS, FET, MOSFET ou que se sabe serem sensíveis à eletricidade estática) são enviados em tubos antiestáticos, espuma antiestática, fita de bobina antiestática, bandeja antiestática e saco antiestático. OPÇÕES DE ENTREGA LOCAL: para possivelmente poupar muito dinheiro SH, veja: Opções locais de pick-up e entrega. Obrigado pela visita ao nosso site da ABQ Techzonics. O melhor dos sucessos. John J. Williams, M. S.E. E. Consumertronics. net Collectible Integrated Circuits Transceptores de coleção Collectible Semiconductors Peças eletrônicas de coleção (pequenas) Peças eletrônicas de ouro Tubos de vácuo de coleção: VINTAGE 2N1555 GERMANIUM TRANSISTOR RARE GERMANIUM POWER TRANSISTOR 15A, 80V, hFE: 30-60, PNP, Electronic Transistors New old stock (NOS ). Rare, Vintage TO-3 pacote (pacote TO-220 muito mais comum). Rare 2N1555 PNP Germanium Power Transistor, fabricado por Transistores eletrônicos. 80V, 15A, hFE 30-60. Ótimo para áudio (por exemplo, fuzz de guitarra e rolo de amplificador de rocha) - não pode ser combinado por transistores de potência de silício na qualidade de som da música. A venda é para um (1) transistor de potência do transistor Germanium de 2N1555. Ótimo para reparar velhas caixas de música. Grande transistor colecionável e colecionável de música. QUANTIDADE LIMITADA. Nós apenas temos alguns deles. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD159. - Preço: 19.95. (5) RSD 2N526 GERMANIUM PNP TRANSISTORS RARE ORIGINAL ROCK amp ROLL MUSIC TRANSISTORS, Gold Leads Novo estoque antigo (NOS) TO-5. Raro original vintage RSD 2N526 Germanium PNP Transistors, 0.5A 30V, 0.23W, Hfe 40-100. Longo ouro leva (muito mais do que mostrado na imagem). Os transistores de germânio são especialmente preferidos para aplicações de música (por exemplo, 2N526 usa efeitos de som de pedal de violão Wah-Wah) - para sons clássicos autênticos da música rock and roll dos anos 60. Os transistores de silício (ou seja, transistores modernos) acreditavam por muitos para produzir sons de rolo de amplificador de rocha inferior - não há substituto de silício para os transistores originais de germânio. Se você é como nós, você preferiria rolar o rolo do amplificador do que a valsa. Além disso, uma grande tecnologia colecionável, transistor colecionável e colecionador de música. VOCÊ QUER ESTE MISMO ARTIGO EM UMA MUITA QUANTIDADE E NO PREÇO DA PERDA DA UNIDADE E DOS CUSTOS DA PAR-UNIDAD SHAN PARA ESTE ARTIGO SE SOB, ENTRE EMAIL NÓS E CONSIDERAMOS SERIAMENTE A LISTA DA QUANTIDADE QUE VOCÊ PRECISA DE EBAY. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD120. - Preço: 34.95. (Desculpe, vendemos recentemente essas duas grandes baterias Eveready Energizer No. 266, Neda 1605 que estamos procurando por mais.) Usado. Baterias de transistor Eveready de 9 volts raras, baterias Energizer, No. 266, NEDA 1605. Estas baterias de zinco-carbono são fabricadas pela Union Carbide. Essas baterias Eveready 9V são praticamente antiquadas agora - este tipo de bateria não foi feito há décadas. De volta ao dia, essas baterias de 9V eram comumente usadas em rádios, de modo que o termo, as baterias de rádio de 9 volts ainda são aplicadas em baterias modernas de 9V. Grande coleção de eletrônicos colecionáveis ​​e coleções de tecnologia. Ou dissecá-los para ver como as baterias de zinco-carbono foram feitas de volta no dia. As baterias estão completamente esgotadas e não são baterias recarregáveis. QUANTIDADE LIMITADA. Nós temos apenas um lote dessas para vender. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD170. - Preço: 39.95. RARE MINCO GOLD PLCC IC, 77B27C018-2001 77B 27C018 MIL-SPEC IC COLLECTIBLE, NÚMERO SERIE NUNARIO New Stock antigo (NOS). Rare Minco Mil-Spec PLCC Gold IC, 77B27C018-2001 77B 27C018 (provavelmente ICs de memória EPROM). Número único e numerado individualmente na série mostrada. Estes não são apenas grandes colecionáveis ​​de IC, mas também têm outros usos valiosos, por exemplo, embutidos em jóias (por exemplo, colares, pingentes, anéis, brincos, pulseiras, pulseiras, tachinhas, abotoaduras, encantos, etc.), ornamentos, decoração , Exibidos e integrados em artesanato e obras de arte, tudo de maneiras que não danificam o IC. Hoje, as jóias com ouro facilmente custam 100s e milésimos - estes são baratos em comparação. Enviado em espuma antiestática. O (s) que você recebe pode não ser os números mostrados na imagem. QUANTIDADE LIMITADA. Nós temos poucos deles à esquerda. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da Lista: LD121. - Preço: 18,95 cada, apenas 8 ainda disponíveis, SH: 7,90 para o primeiro, 1,50 para cada IC adicional. RARE MINCO GOLD PLCC IC, 77B27C018-2001 77B 27C018 MIL-SPEC IC COLLECTIBLE, NÚMERO SERIE NUNARIO New Stock antigo (NOS). Rare Minco Mil-Spec PLCC Gold IC, 77B27C018-2001 77B 27C018 (provavelmente ICs de memória EPROM). Número único e numerado individualmente na série mostrada. Estes não são apenas grandes colecionáveis ​​de IC, mas também têm outros usos valiosos, por exemplo, embutidos em jóias (por exemplo, colares, pingentes, anéis, brincos, pulseiras, pulseiras, tachinhas, abotoaduras, encantos, etc.), ornamentos, decoração , Exibidos e integrados em artesanato e obras de arte, tudo de maneiras que não danificam o IC. Hoje, as jóias com ouro facilmente custam 100s e milésimos - estes são baratos em comparação. Enviado em espuma antiestática. O (s) que você recebe pode não ser os números mostrados na imagem. QUANTIDADE LIMITADA. Nós temos poucos deles à esquerda. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da Lista: LD121. - Preço: 18,95 cada, apenas 17 ainda disponíveis, SH: 7,90 para o primeiro, 1,50 para cada IC adicional. RARE, VINTAGE 40536 TRANSISTOR w GOLD PLATED Amplificador HEATSINK, CAIXA ORIGINAL, RCA Novo estoque antigo (NOS). Raro, vintage 40536 Transistor com banhado a ouro, dissipador de calor embutido e caixa original, RCA. O 40536 foi feito antes da convenção 2N surgiu e quando o chapeamento de ouro era comum, e agora é tão raro que não podemos encontrá-lo listado em qualquer lugar O 40536 é enviado na sua caixa original. QUANTIDADE LIMITADA. Nós temos apenas dois desses. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD139. - Preço: 99,95 Novo estoque antigo (NOS), selado na embalagem original. Muito raro Herman H. Smith 3513 Transistor, HEP-715 Equivalente. Na verdade, este transistor é EXTREMAMENTE RARO - um dos poucos transistores já feitos em Brooklyn, NY. HH Smith era conhecido principalmente por intrusos de cerâmica e pistas de teste eletrônicas. Grande colecionador eletrônico. QUANTIDADE LIMITADA. Nós temos apenas um desses. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD132. - Preço: 199.95. Novo estoque antigo (NOS). Rare, vintage TI 3033 Power Transistor pair, provavelmente RF. O par transistor 3033 parece dourado. Compramos este item extremamente raro em uma venda imobiliária (engenheiro elétrico de Los Alamos) em uma caixa rotulada, quase Transistor de 1960. Não sabemos nada sobre este item, além disso. Grande collectible. QUANTIDADE LIMITADA. Nós temos apenas um desses. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD122. - Preço: 199,95 - Se você acredita que o preço é muito alto, os vendedores de documentos vendem por menos e consideraremos seriamente a redução do preço. Novo estoque antigo (NOS). Rare, vintage TI 3032 Power Transistor, provavelmente RF, em pacote original fechado, como mostrado. O transistor 3032 parece dourado. Compramos este item extremamente raro em uma venda imobiliária (engenheiro elétrico de Los Alamos) em uma caixa rotulada, quase Transistor de 1960. Não sabemos nada sobre este item, além disso. Grande collectible. QUANTIDADE LIMITADA. Nós temos apenas um desses. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD122. - Preço: 99.95 - Se você acredita que o preço é muito alto, os vendedores de documentos vendem por menos e consideraremos seriamente a redução do preço. Novo estoque antigo (NOS). Vintage Fairchild S4149 dos anos 1960, 324 Dispositivos planar de silício. Cada um é rotulado com quot12 03quot no topo. Podem ser transistores, não sabemos. Se os transistores, podem ser bipolares, FET, UJT, ou talvez tiristores. Longo ouro leva. Grandes coleções. O tipo de caixa que eles vieram é mostrado na imagem, mas não está incluído nesta venda. QUANTIDADE LIMITADA. Temos apenas alguns conjuntos destes. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD122. - Preço: 29.95 Novo estoque antigo (NOS). Vintage 1960's Fairchild 911218 227 Silicon Planar Devices. Podem ser transistores, não sabemos. Se os transistores, podem ser bipolares, FET, UJT, ou talvez tiristores. Longo ouro leva. Cada dispositivo plano de silício possui uma pequena gota de tinta vermelha, o que geralmente significa que os dispositivos planar de silício foram selecionados para algumas propriedades importantes, geralmente ganham, então é provável que eles estejam combinando dispositivos planos de silício. Grande collectible. O tipo de caixa que eles vieram é mostrado na imagem, mas não está incluído nesta venda. QUANTIDADE LIMITADA. Temos apenas alguns conjuntos destes. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD122. - Preço: 29.95 RARE VINTAGE 2N297A, 2N297-Type, GOLD-PLATED PNP GERMANIUM POWER TRANSISTOR, Motorola Novo estoque antigo (NOS), TO-3 pacote. Raro Motorola 2N297A PNP Germanium Power Transistor. Motorola 2N297A está em pacote de plástico original selado (foto tirada através da embalagem). 35W, 60V, hFE cerca de 70. Grande colecionador eletrônico. Os transistores de germânio são especialmente preferidos para aplicações de música e são grandes colecionáveis ​​eletrônicos. Estes raros transistores 2N297A têm uma saia banhada a ouro em torno da tampa superior de aparência de alumínio e cabos banhados a ouro. Enviado em pacotes selados originais. QUANTIDADE LIMITADA. Apenas alguns sobraram. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD120. - Preço: 8.95 RARE ADC0801LCD ADC 0801LCD ADC0801 CIELO DO OURO, CONVERSOR DE AD CONHECIMENTO DE 8 BITS (ADC) IC National Semiconductor Novo estoque velho (NOS) DIPDIL. Extremamente raro ADC0801LCD ADC 0801LCD ADC0801 IC de ouro, conversor AD de 8 bits (ADC) IC, National Semiconductor. Foi-nos dito (mas não podemos verificar) que o quot003quot representa o 3º lote deste National Semiconductor já feito. Ouro ADC0801LCD IC enviado em espuma ou tubo antiestático. QUANTIDADE LIMITADA. Apenas alguns sobraram. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD120. - Preço: 39.95 Novo estoque antigo (NOS) DIPDIL IC. Ouro Intel C1101A. Estes raros Intel C1101A Gold IC são um incrível encontrar 16 pinos, cerâmica. Consiste em dois tipos diferentes, como mostrado - um tipo é branco opaco, o outro mais transparente. Nós temos um número limitado desses incriveis e lindos argumentos de cobrança sobre uniformemente divididos entre os dois tipos, e nós escolheremos aleatoriamente aquele para você quando você os comprar. Enviado em tubo antiestatico ou espuma antiestática. O Intel C1101A IC, de acordo com o Guia de Coletores para Microchips Vintage Intel, é avaliado em 20-80 cada, dependendo da condição, onde novas condições não utilizadas, como esses ICs, estão no topo. Ouro C1101A enviado em tubo antiestatico ou espuma. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD096, LR097-S01. - Preço: 49.95 RARO, OURO WD33C93-AL WD33C93AL WD33C93 WD 33C93 INTERCÂMBIO DE INTERFACE DE INTERFACE SCSI AMPLIFICADO DIGITAL DIGITAL DIGITAL IC novo DIPDIL IC LSI de 40 pinos de estoque velho (NOS). Rar, pristine Western Digital WD33C93-AL WD33C93AL WD33C93 Controlador de Interface de barramento SCSI Enhanced de tipo WD 33C93. O WD33C93 é compatível com os Advanced Microdevices AM33C93 AM 33C93 e outros controladores de interface de barramento SCSI 33C93 e é usado para controlar unidades de disco magnéticas (por exemplo, discos rígidos) e unidades de disco óptico (por exemplo, CDROMs). A placa da caldeira WD33C93-ALs, todas as 40 pistas e a faixa superior são todas douradas. Raras e valiosas. Bonito e precioso colecionável. Ouro WD33C93-AL enviado em tubo antiestatico ou espuma. QUANTIDADE LIMITADA. Muito poucos desses conjuntos valiosos e populares deixaram. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD107. - Preço: 14.95. Novos recursos de estoque antigo (NOS) DIPDIL. Memórias monolíticas (agora Vantis) ouro MMI5306. Estes raros ICs de ouro MMI 5306-1D são um incrível DIPDILs de 16 pinos, de cerâmica. Consiste em dois tipos diferentes, como mostrado - um tipo é branco opaco, o outro tipo é roxo. Temos um número limitado de incrivelmente raros e bonitos colectáveis, a maioria dos quais são de cerâmica branca, e escolheremos aleatoriamente os dois para você quando você os comprar. Ouro MMI5306 enviado em tubo antiestático ou espuma antiestática. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD096. - Preço: 19.95 RARE, VINTAGE MHS ​​80C52268-GOLD 8-BIT MICROCONTROLLER, Intel, 1982 Novo estoque antigo (NOS), DIPDIL. Rare, Vintage MHS 80C52268-Gold 8-Bit Microcontroller, Intel, 1982. Fabricado na América - não da China. Placa de ouro, alfinetes de ouro e listra de ouro. 80C52268 IC de ouro enviado em espuma ou tubo antiestático. Nós também vendemos o plástico MHS 80C52268 na nossa página do microcontrolador. QUANTIDADE LIMITADA. Temos apenas uma dessas. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD137. - Preço: 99.95 RARE, VINTAGE INS8080AD-GOLD INS 8080AD 8080 C8080A (C8080 FAMILY), National Semiconductor Novo estoque antigo (NOS), DIPDIL. Raro, Vintage INS8080AD-Gold INS 8080AD 8080. C8080A (família C8080), National Semiconductor, data desconhecida, mas provavelmente final dos anos 1970 - início dos anos 80. American made - não da versão da China. Placa de ouro, alfinetes de ouro e listra de ouro. INS8080AD IC de ouro enviado em espuma ou tubo antiestático. QUANTIDADE LIMITADA. Temos apenas uma dessas. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD137. - Preço: 79.95 RARE, VINTAGE AM9519DC-GOLD AM 9519DC, 9519-Tipo UNIVERSAL INTERRUPT CONTROLLER, AMD 1978 Novo estoque antigo (NOS), 28 pinos DIPDIL. Rare Vintage AM9519DC-Gold AM 9519DC, 9519-Type, Controlador de interrupção universal, AMD 1978. Placa de ouro, alfinetes de ouro, cabos de ouro. American made - não da versão da China. AM9519DC IC de ouro embarcado em espuma ou tubo antiestático. QUANTIDADE LIMITADA. Temos apenas uma dessas. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD137. - Preço: 129.95 Novo stock antigo (NOS), SMTSMD. Raro, Vintage RCA CRC JM3851005503BZA, CD4049 equivalente. O quot351cquot é, aparentemente, um número de lote exclusivo para esta parte específica. Este raro JM3851005503BZA IC é um excelente colecionável. JM3851005503BZA IC embarcado em sua embalagem original como mostrado. QUANTIDADE LIMITADA. Temos apenas alguns lotes disso. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD137. - Preço: 10.95 RARE TI TPS2013 TPS-2015 KIT RARE CURRENT PROTECTED DISTRIBUTION SWITCH E TPS2013 EVALUATION BOARD, Texas Instruments Novo estoque antigo (NOS). Rare TI TPS2013 TPS-2015 Interruptor de Distribuição de Proteção de Corrente e TPS2013, Texas Instruments. Este kit TPS2013 é um instrumento de teste útil e também um excelente colecionador eletrônico. TPS2013 enviado em sua embalagem original selada como mostrado. QUANTIDADE LIMITADA. Temos apenas uma dessas. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD137. - Preço: 39.95 RARE INTEL CHMOS KIT, 1983 quotLow Power - High Performance Kit Solutionquot 87C64 LATCHED EPROM 51C86 iRAM 80C31 MICROCONTROLLER Novo estoque antigo (NOS), DIPDIL ICs. Rare Intel CHMOS Kit - quotLow Power - Solução de Kit de Alto Desempenho, em 1983, consistindo em um cada 87C64 Bloqueado EPROM, 51C86 iRAM e 80C31 Microcontoller. O kit Intel CHMOS é enviado na caixa de vidro original como mostrado (a caixa possui uma fenda no lado inferior direito, não mostrada devido ao brilho do flash da câmera). QUANTIDADE LIMITADA. Temos apenas uma dessas. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD137. - Preço: 39,95 Novo estoque antigo (NOS) DIPDIL ICs. Rare 41P WE0155, pinos de ouro. Esses CIs 41P W E0155 retornam aos anos 70 quando eles rotineiramente fizeram ICs com pinos de ouro, provavelmente funcionalmente de pouco uso hoje. No entanto, eles são grandes colecionáveis, e o chapeamento de ouro nas pistas é importante para alguns. Não encontramos as especificações em nenhum desses ICs. Você receberá WE0155, WE0845 ou WE0796, dependendo do tubo que extraímos aleatoriamente (se você tiver uma preferência, avise-nos e por que sua preferência). Se você sabe alguma coisa sobre suas especificações, avise-nos. Foi-nos dito, mas não conseguimos verificar se eles foram feitos pela Westinghouse Electric. Ouro WE0155 enviado em tubo antiestático. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD100. - Preço: 29.95 Novo stock antigo (NOS) Burr Brown VFC62BG DIPDIL IC. Este ouro raro Burr Brown IC é um excelente colecionador. Nós não conhecemos o Burr Brown VFC62BG IC. Ouro VFC62BG enviado em tubo antiestatico ou espuma. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD099. - Preço: 59,95 Novo estoque antigo (NOS) Burr Brown MPY100AG DIPDIL IC. Este ouro raro Burr Brown IC é um excelente colecionador. Nós não conhecemos o Burr Brown MPY100AG IC. Ovo MPY100AG enviado em tubo antiestatico ou espuma. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD099. - Preço: 59.95 RARE AD536AJD AD 536AJD, AD 536-tipo, CONVERSOR RMS-TO-DC, DISPOSITIVOS ANALOGICOS IC GOLD IC Novo estoque antigo (NOS) DIPDIL IC. Analog Devices AD536AJD circuito integrado de ouro, conversor RMS para DC. O AD536A AD536 IC é um conversor RMS para DC. Este raro Gold Analog Devices IC é um grande collectible. Ouro AD536AJD enviado em tubo antiestatico ou espuma. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD099. - Preço: 59.95 OURO RARO Motorola MC68000L8D MC 68000 PROCESSADOR DE MULTIPROTOCOLO INTEGRADO, MICROPROCESSADOR DE COMPUTADOR DE MAÇAS (MPU) Novo ouro antigo (NOS) ouro raro Motorola MC68000L8D MC 68000 Processador Multiprotocolo Integrado, Microprocessador Apple Computer (MPU), DIPDIL de 64 pinos. Gold MC68000 é enviado em tubo ou espuma antiestática. QUANTIDADE LIMITADA. Este é o último à esquerda. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD108. - Preço: 39,95 Novo estoque antigo (NOS) DIPDIL ICs. ICs de microcontrolador de ouro Intel 80C5226B. Este item é para 3 desta grande coleção de eletrônicos, um ouro como mostrado e dois de plástico. Nós não sabemos o que são, talvez alguma forma de microcontrolador ou microprocessador como a série de microcontroladores 80C3180C3280C5180C52. Você sabe o que são Gold 80C5226B enviado em tubo antiestatico ou espuma. COMPRADOR: Ordem por Título (abaixo da imagem) - Envie-nos seu pedido. - Histórico da lista: LD100. - Preço: 19,95 (6) RARE RM217T-7106 RM 217T ICs RAYTHEON E GATE DIODE LOGIC, GOLD LEADS Novo estoque antigo (NOS). Rare Raytheon RM217T-7106 ICs RM 217T, e lógica de diodo de portão. Gold leva. QUANTIDADE LIMITADA. Nós temos apenas um desses. BUYER: Order by Title (below image) - Email us your order . - List History: LD132. - Price: 59.95 VINTAGE TDA7000 TDA 70000, FM RECEIVER ARCHER TANDY RADIO SHACK RS 276-1304 COLLECTIBLE New Old Stock (NOS). Vintage Radio Shack Archer Tandy TDA7000 TDA 7000 FM Receiver, RS 276-1304. Comes sealed in its original glassine package. Package also includes its datasheet with specifications and circuit designs described on it. Image of the IC itself was shot through its glassine pocket, so it looks less sharp than if TDA7000 was outside the package. Great electronics collectible or you can use the TDA7000 for electronic project. LIMITED QUANTITY. We have only a few left of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD121. - Price: 19.95 RARE, VINTAGE AN5310 COLOR TVMONITOR IC EQUIV. TDA3570, KA2150, UPC1352C IC (NTSC DECODER) New old stock (NOS), DIP. Rare, vintage AN5310 TVMonitor IC (NTSC Decoder), probably made by Panasonic, in original package (opened only to photograph). Equivalent to TDA3570, KA2150, and UPC1352C. We do not know part function. Great electronic collectible. AN5310 IC shipped on antistatic foam in its original package. LIMITED QUANTITY. We have only one of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD122. - Price: 9.95 RARE, VINTAGE CN5411 TVMONITOR IC EQUIV. AN5411, CX557, ECG1299 IC New old stock (NOS), DIP. Rare, vintage CN5411 TVMonitor IC, equivalent to AN5411, ECG1299 and CX557 IC, probably made by Panasonic. In original package (opened only to photograph). We do not know part function. Great electronic collectible. CN5411 IC shipped on antistatic foam in its package. LIMITED QUANTITY. We have only one of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD122. - Price: 17.95 (2) RARE FARADAY FE3010B FE 3010B PERIPHERAL CONTROLLER ICs, IC for AMIGA COMPUTERS, COMMODORE 64 COMPUTERS, COMMODORE 128 COMPUTERS New old stock (NOS) FE3010 Faraday 84-pin PLCC. If Amiga computers and Commodore computers are part of your legacy, or you are trying to repair one with a bad or suspect peripheral controller, you absolutely MUST buy these FE3010 Peripheral Controller ICs Also makes great collectible ICs DO YOU WANT THIS SAME ITEM IN A GREATER QUANTITY AND AT CHEAPER PER-UNIT PRICE AND PER-UNIT SH COSTS THAN THIS ITEMSEE DETAILS AT TOP OF THIS WEBPAGE. BUYER: Order by Title (below image) - Email us your order . - List History: LD096. - Price: 19.95 (5) RARE RC3403A RC 3403A GROUND-SENSING QUAD OPAMP ICs Fairchild Semiconductor New old stock (NOS) DIPDIL. Rare Vintage RC3403A-RAYC8030 Ground-Sensing Quad Opamp, Fairchild Semiconductor. RC3403A is pin-compatible with LM324, TL084, etc. and is compatible with MC3403 (which we also sell), UA3403 and XR3403CP. The RC3403A is a great electronic collectible as well as useful for audio and lower-frequency applications. RC3403A shipped in antistatic tube or foam. LIMITED QUANTITY: We only have a few of these left now. BUYER: Order by Title (below image) - Email us your order . - List History: LD120. - Price: 14.95 Most appear to be New Old Stock (NOS), some in original bags. We have not counted them but they appear to be about 100 gold-plated ICs and transistors. Various part numbers, most rare. LIMITED QUANTITY. We have only one of these bags. BUYER: Order by Title (below image) - Email us your order . - List History: LD121. - Price: 39.95 RARE VINTAGE Motorola 2AD149, GOLD LEADS GERMANIUM TRANSISTOR, PNP, POWER, TO3 New old stock (NOS) transistor with gold leads. The incredible 2AD149 monolithic transistor pair is a discontinued transistor. The suggested replacement is the NTE121MP, which is priced at 42.50 each V(BR)CEO30 volts, Ic3.5 Amps. Pd Max32 watts, Ft(min)300 KHz. The 2AD149 was and still is to some extent used in stompboxes by musicians who need to reproduce the distinctive tonal character of the quotfuzzquot-tone from the early rock amp roll era. In other words, if you truly want to produce that classic rock sound the way it was produced back then, you must go with germanium transistors. When it comes to music, there are important differences between silicon transistors and germanium transistors Stomp boxes (e. g. the Ibanez TS9 Tubescreamer) - also known as effects pedals - is a sound effects unit usually housed in a small metal chassis, popularly used by musicians (usually electric guitar players as a guitar effects pedal, but sometimes by players of other instruments including keyboards, bass, violin and cello). These popular sound effects devices alter the sound quality (i. e. timbre) of the inputted signal - adding effects such as fuzz, distortion, boost, overdrive, chorus, reverberations, flanging, phaser, wah-wah and pitch-shifting. A guitar or other instrument played without the special effects of an effects pedal is typically described as quotstraightquot or quotcleanquot and sounds far less interesting to music philes. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 9.95 New old stock (NOS). Rare, vintage Fairchild F8-6-16-832 Transistor, Gold leads. Unknown function (do you know what these are). LIMITED QUANTITY. We have only few of these left. BUYER: Order by Title (below image) - Email us your order . - List History: LD135. - Price: 9.95 New old stock (NOS). Rare Vintage GE C122B, Gold Leads. We are not certain what functions these have (do you) because we cant locate their datasheets. Our recollections are that the GE C122B were triacs or SCRs thyristors. LIMITED QUANTITY. We have only few of these left. BUYER: Order by Title (below image) - Email us your order . - List History: LD135. - Price: 9.95 RARE MC1433G, MC1433-type LINEAR IC OPAMP IN THE CAN, GOLD LEADS, Motorola New old stock (NOS), 10-pin can. Rare MC1433G, MC1433-type Linear IC, in the can with gold leads, Motorola Opamp. Great electronics collectible. MC1433G Opamp shipped on antistatic foam. LIMITED QUANTITY. We have only two of these left. BUYER: Order by Title (below image) - Email us your order . - List History: LD135. - Price: 19.95 New old stock (NOS), 64-pin DIPDIL. Legendary Zilog Z180 MPU Z8018006PSC, Z8018006-PSC, CPU, 6 MHz. The Zilog Z180 while still useful in some older technology today, it is also a great electronics collectible. Zilog Z180 Microprocessor Unit is shipped in antistatic tube or foam. DO YOU WANT THIS SAME ITEM IN A GREATER QUANTITY AND AT CHEAPER PER-UNIT PRICE AND PER-UNIT SH COSTS THAN THIS ITEM IF INTERESTED IN BUYING MORE OF THESE, PLEASE EMAIL US. BUYER: Order by Title (below image) - Email us your order . - List History: LD135. - Price: 11.95 New old stock (NOS). Microwave diodes radar diodes Gunn diodes. These are sealed in lead as shown. We do not know what they are, they came in box marked, quotGunn Diodes, quot and without removing them from the lead, we have no way of knowing what the part numbers are. You will just have to take your chances. Gunn diodes are commonly used in police doppler radars. These Gunn diodes are vintage American made (all the other parts, except some of the ICs, in the lot were 1970s-1980s vintage American-made electronic parts). So these microwave diodes are not the commonly sold Online USSR Gunn diodes. Nor are these microwave diodes the unpackaged ones commonly sold Online that may or may not be used burned-out Gunn diodes. LIMITED QUANTITY. We have only one of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD122. - Price: 29.95 (2) RARE SOLID STATE HIGH-VOLTAGE RECTIFIER TUBES SYLVANIA ECG, ECG 511R-2AV2, ECG 512R-DW4 New old stock (NOS), sealed in original packages. Rare Solid State High-Voltage Rectifier Tubes, Sylvania ECG, ECG 511R-2AV2, ECG 512R-DW4. Equivalents for R-2AV2, 1V2, 2AV2, R-DW4, 6DW4, 6CK3, 6CL3, 6BA3 high-voltage rectifier tubes. LIMITED QUANTITY. We have only one of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD132. - Price: 29.95 New old stock (NOS) in original box. Rare Donnor-Winfield DPS1 Crystal Oscillators, 8640 Hz. Great electronics collectible. LIMITED QUANTITY. We have only one of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD132. - Price: 29.95 New old stock (NOS). Rare, vintage MR322R 1N3491R Power Rectifiers, Motorola. Great electronic collectible (circa 1970s) and vintage electronic repair and electronic restoration projects. The MR322R 1N3491R power diodes come in their original, sealed package as shown. LIMITED QUANTITY. We have a few of these left. BUYER: Order by Title (below image) - Email us your order . - List History: LD122. - Price: 14.95. New old stock (NOS). 6GW6 Vacuum tube. If you are interested in us carrying more vacuum tubes, please let us know, and the specific part numbers you seek. LIMITED QUANTITY. We have only one of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD145. - Price: 11.95. Collectible Electronic Kits Collectible Electronic Parts (large) Collectible Electronic Materials: RARE LARGE PHENOLIC BOARD, HIGH-VOLTAGE, 8-12quot x 17quot x 18quot, VECTORBORD PERF BOARD (Sorry, we are now out of this popular board, but believe we can get more soon if interested, please email us to get on our list). New old stock (NOS). Rare, large vintage perforated Phenolic Board, high-voltage, 8-12quot x 17quot X 18quot Vectorbord Perforated Board. Holes are 0.1quot diameter, with hole-to-hole spacing of about 0.265.quot There are 32 holes each row and 64 holes each column (2,048 holes total). Phenolic has great properties, and numerous phenolic applications, especially high-voltage applications. Phenolic properties include: Resistance to high-voltages (excellent dielectric strength), excellent electrical insulator and thermal insulator, light weight, easily machinable, good mechanical strength and dimensional stability, retains chemical structure and rigidity at high temperatures, doesnt corrode or spark, low moisture absorption and high humidity resistance, excellent resistance to chemicals (e. g. acids, lubricants, cleaning solutions), excellent resistance to splitting and splintering. Phenolic uses include: Terminal boards, switching gear and panels (especially high-voltage switchers), bearings, gears, wear strips, gaskets, washers, transformers, machined small parts, industrial laminates, displays, packaging, partitions, project boards, robotics, crafts, and explosives applications. Used in many antique radios and other antique electronics equipment and vintage military equipment, so ideal for antique radio antique electronic and vintage military equipment repairs, restorations and modifications. Also these phenolic boards, especially phenolic perf boards, make great robotics platforms, printed circuit board backups, for mounting large components, and to insulate the insides of electronic enclosures and electrical enclosures. Also, the phenolic board through holes (perforations) are great starter holes for drilling and punching, mountings, running wires, and for ventilation, lighting and sifting. Because of phenolics special properties, if you do electronic, electrical or mechanical projects, repairs, restorations and modifications, this phenolic board is an important versatile material to keep on hand. LIMITED QUANTITY. We have only a few of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD122. - Price: 24.95 RARE, VINTAGE VARIABLE CAPACITOR, VARIABLE TUNING CAPACITOR, 5-SECTION Used and in great condition. Great for the ham operator, electrical engineer, electronic engineer andor technician. We cant find a marking as to who made it. It has a tuning gear assembly for precision tuning. Has 5 sections (5-bank). We cant find a boiler plate on it, so we dont know who made it. Great electronics collectible. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD061, LS092-R20. - Price: 39.95. SH: 9.90 I bought this stunning item at an estate sale of a collector which also featured rare antique Atwater radios and Philco test equipment (sold in my webpages) and other rare, vintage and antique mostly radio electronics. In the decades We have actively searched for rare vintage and antique electronic equipment, this is the very first one of these we ve ever run into we was told by a family member of the deceased that it is an antique telegraphers vacuum tube assembly dating back to about the 1920s. During months of searching, we have tried to verify this and find out more information about this Item, but have had no success, so We are not certain that this is a telegraphers tube assembly or when it was made. It possibly could be a lamp to a very old projector or spotlight assembly as a few people have told me, however, since it is coated opaque black at the top, it is difficult to see how it was used as a lamp. There are no markings on the base or on the tube. There is something handwritten inside the tube on its molded glass part, but we cant read it, looks like gold or yellow ink. The tube pushes and twists to lock into place with similar action as that of a bayonet type light bulb used in car lights or a medicine bottle (tube base is not threaded). Assembly is 7-12quot x 4-12quot (at widest point). The tube itself is 5-12quot x 1-14quot diameter. The tube socket looks like it is made of bronze. We have left the small remnants of the original wiring still connected. The Item is in great condition with a little rust near the screws on the top and the mechanism at the bottom, and a small hairline split in edge of the base (see left image). Base and standoffs appear to be made of a phenolic-like material but we are not sure. Base is actually brownish-reddish in color, purple coloration of image is due to photo underexposure. We have only one of these and we probably will never see another one again, so when it is sold, there are no more. UNIQUE ITEM. This is the only one. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 29.95. SH: 11.90 RARE, VINTAGE RCA AIRCRAFT BAND CONVERTER KIT VHF CONVERTER KIT, KC4007A New. We opened up the package just to photograph it. Includes everything: The parts, the pre-punched aluminum enclosure, the instructions, and the schematic. Very nice radio collectible electronics collectible. BUYER: Order by Title (below image) - Email us your order . - List History: LD093. - Price: 49. SH: 9 RARE, VINTAGE CIRCUITRON AR-1 AUTOMATIC REVERSE KIT MODEL TRAINS MODEL RAILROAD SYSTEMS, OTHER USES New old stock (NOS). Rare, vintage Circuitron AR-1 Automatic Reverse Kit for Model Railroad Trains. Can also be used for many other applications. LIMITED QUANTITY. We only have one left. BUYER: Order by Title (below image) - Email us your order . - List History: LD121. - Price: 49.95 RARE, VINTAGE PIKO MODELLBAHN ME 005, BR 55 (HO) RAILROAD TRANSFORMER FOR MODEL RAILROADS TRAINS Model Railroad isolation transformer. Used. Apparently German-made. Comes with a European-type AC power connector (see image left side). We have not been able to test model transformer, so its condition is unknown to me, and we cannot guarantee condition. We bought it at an estate sale (others got the train sets). 220 VAC, 33.6VA, 50 Hz input 1.7 - 12 VDC, 1.2A 1st output (Bahn), 16 VAC, 1.2A 2nd output (Zubehor). 8quot x 4-34quot x 4quot. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD061, LS092-R25. - Price: 74.95. SH: 9, 7 lbs (Sorry, we recently sold this TM-184 connector board we are looking for more.) Vintage heavy-duty TM-184 connector board . Used but in very good condition. 28 (14 pair) large knurled connection posts for high current uses. 38quot thick composite board that looks like it is phenolic board. The knurled posts are unscrewed up, the bare wire is inserted in a notch, and then screwed down tight again. Weighs 3 lbs. UNIQUE ITEM. We have only one of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD107. - Price: 49.95. SH: 11.90 (9) LAMP BEZELS (Red amp Purple from Military Equipment) Used and in very good condition. Very high quality metal construction with faceted type bezel glass. The left image shows what the two colors are when a light shows through them. The right image shows what they look like on their sides and bottoms. They are threaded at the base, and they require a 916quot round hole. These were salvaged from very expensive military equipment. While about 80 of my supply are red and 20 purple, If you specify how many of the 9 you wish to be red or purple, we will try to provide those proportions however, we cannot guarantee what of each color you will get. Since these come from military equipment several decades old, they make a great electronics collectible and military collectible. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 8.95 (4) RARE, GLASTIC ELECTRICAL INSULATORS ELECTRICAL ISOLATORS ELECTRICAL STANDOFFS ELECTRICAL MOUNTS Used but in good conditions. These Glastic high-voltage plastic electrical mountings are perfect for many medium-size electrical insulating applications. Also great for various other general mounting applications such as for equipment standoffs, furniture standoffs and other mechanical standoffs, and as part of vibration isolation systems. Centered threaded quarter-inch inserts on both sides (female) the metal threaded insert on one side is not electrically conductive to the one on the other side so they are insulators. 2quot tall x 2quot diameter. These Glastic insulators are both useful and great electrical collectibles. BUYER: Order by Title (below image) - Email us your order . - List History: LD061, LR095-S01. - Price: 24.95 TRANSPARENT DYNAMO FLASHLIGHT DEMONSTRATES ELECTRICITY GENERATION This fascinating flashlight demonstrates the generation of electrical energy using an electrical generated that converts mechanical energy (i. e. the squeezing of the flashlight handle) into electrical energy, and then into light energy (i. e. the flashlight output). The squeeze handle is connected to a fascinating gear and flywheel assembly which drives the dynamo. There is no battery as the flywheel stores the energy. The faster you squeeze, the faster the flywheel turns, and the greater the intensity of the light and the longer the light stays on after you stop squeezing. Great for classroom and scientific demonstration and science fairs. Also great for field, backup or emergency use as you never need a battery, and therefore, you never have to worry about the timing and cost of battery replacements. Of course, this device can be disassembled by removing the screws and then modified to charge a battery, or to provide some other type of electrical or mechanical function. Comes with a built-in spare bulb. Flashlight is shown upside down in image. UNIQUE ITEM. This is the only one. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 24.95 Collectible Electronic Test Equipment Collectible Electronic Tools: RARE, VINTAGE TRIPLETT DIGITAL VOM, MODEL 8000 TYPE 1, w NIXIE TUBES Used and works great. This Triplett VOM is one of the earliest digital volt-ohm meters ever commercially sold A truly rare and beautiful vintage electronic test equipment find, and an incredible collectible. Dont let this one get by you UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD094. - Price: 299.95. SH: 11, 11 lbs VINTAGE CIMRON DMM 40 DIGITAL MULTIMETER Used. Turns ON with display lighting up clear and bright for all settings. We got this in a huge lot of electronics and just dont have time to thoroughly test it so we cant guarantee function or accuracy. Nenhum manual. UNIQUE ITEM. This is the only one. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 24.95. SH: 11, 11 lbs Used and works great. Has a built-in load, as shown, so tests cells under actual and realistic battery working conditions. BUYER: Order by Title (below image) - Email us your order . - List History: LD099. - Price: 59.95. SH: 9.90 Used. Turns ON with all of the display lighting up clear and bright. We got this in a huge lot of electronics and just dont have time or a calibrated pH or ion source to thoroughly test it so we cant guarantee function or accuracy. Nenhum manual. No probe. UNIQUE ITEM. This is the only one. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 29.95. SH: 9, 9 lbs Bought it at an estate sale. Stunning collectible This rare Model 070 Philco Signal Generator goes back to the dawn of the electronics age. We dont know if it works, we have not attempted to test it, and it is sold as is. It is an absolutely terrific collectible In all my several decades of buying and collecting vintage electronics, we have never seen this model 13quot x 10quot x 4.5quot. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD049, LS092-R10. - Price: 349.95. SH: 25, 14 lbs Bought it at an estate sale. A stunning collectible test equipment This rare Philco tester goes back to the dawn of the electronics age. We dont know if it works, we have not attempted to test it, and it is sold as is. It is an absolutely terrific collectable In all my several decades of buying and collecting vintage electronics, this is only the second Philco testing equipment we have ever run into 8quot x 6.5quot x 3quot. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD061, LS092-R25. - Price: 149.95. SH: 15, 7 lbs RARE SPRAGUE MIKE-O-METER, CATS EYE METER, MOTOR CAPACITOR METER, MODEL M-2 Used and works great, and very clean. Beautiful instrument. Some surface rust on the handle on top and external screws, but case in very good condition. We replaced the AC power line with a new one. 5.75 X 8.5 X5quot. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD049, LS092-R20. - Price: 79.95. SH: 12, 8 lbs Vintage wire strippers are used and work good. When new, these types of wirestrippers sell for about 52 each. Very high quality. They are both very useful and great collectibles for the engineer, technician and vintageantique tool collectors. Comes with a print out which describes this type of wire stripper. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD049, LS092-R25. - Price: 34.95 L1 WIRE STRIPPERS, RARE, VINTAGE COMMSCOPE KS16902 KS-16902 Vintage Commscope KS-16902 strippers (L1 strippers) is used and works great. Both useful and a great collectible for the engineer and technician. Comes with a print out that describes it. UNIQUE ITEM. This is the only one. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 19.95 Used and in great functional condition last time we used it. Great as a vintage electronics collectible. And great for the engineer or technician working with high voltage. Kilovolt setting upto 100 KV. The ports on top are used for two glass capacitor high-voltage dividers (not included as we no longer have them). The high-voltage capacitor dividers are about a foot long with the spherical high voltage terminals at the end. However, a skilled technical person probably can fabricate a safe and useful replacement high-voltage dividers made out of high-voltage insulator material less fragile than glass. 11quot x 9quot x 9quot. LIMITED QUANTITY. Unique Item. We have only one of these. BUYER: Order by Title (below image) - Email us your order . - List History: LD096. - Price: 99.95. SH: 17, 17 lbs RARE, VINTAGE BIO-FEEDBACK TECHNOLOGY, INC. ELECTRONIC BIO-FEEDBACK THERMOMETER MODEL BFT 301 BFT301, w RARE PROBES amp USER MANUAL for BIOFEEDBACK, MIND CONTROL, BEHAVIORAL CONTROL, BRAINWAVE ENTRAINMENT, RESEARCH (Sorry, sold out of this great BFT301 BFT 301 Biofeedback Thermometer we are trying to obtain more.) Used but worked great last time we used it. Electronic biofeedback thermometer is portable and battery-operated. Generally employed for biofeedback, relaxation and stress reduction, and in mind control and brainwave entrainment research. It is 10.5quot x 8quot x 4.5quot, and built into a strong case, with a big easy-to-read meter. COMES WITH PROBES AND MANUAL. The two big, Eveready Energizer No. 266 (Neda 1605) 9-volt batteries it came with are depleted. We do not have replacements for these batteries however, the power connectors to the system can be easily re-wired for the 9-volt radio batteries and 9-volt DC power adapters commonly used today. We did not make this change because vintage equipment collectors prefer that such rare, vintage equipment be left as much in its original condition as possible, and new or rechargeable No. 266 batteries may be still available somewhere. Will be shipped without batteries installed. Since We have not been able to test this system, we are selling it quotas is. quot This is part of a number of pieces of equipment and books and manuals we are selling Online related to my several years of research into Mind Control, Subliminal Mind Control, Electronic Attack, Electronic Harassment, Brain wave Entrainment (or Brain Entrainment), Brainwashing, Body Control, Behavioral Modification, Electronic Implants, and Biofeedback for Consumertronics. net of Albuquerque, NM (books, manuals, research, consulting), and Lone Star Consulting, Inc. of El Paso, TX (hardware, consulting). My related Consumertronics. net books and manuals (including ebooks) have the titles of, quotMind Control, quot quotSubliminal Mind Control, quot quotElectromagnetic Brainblaster, quot and quotUnder Attackquot. Again, browse and search my webpages. We have such a huge amount of equipment related to this type of research, much of it duplicate or similar to each other, that we are now selling some of my surplus. - Thanks, John J. Williams, M. S.E. E. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD049, LS092-R20. - Price: 29.95. SH: 10, 6 lbs RARE, VINTAGE DIGIAC CORP. ELECTROLAB WOUND ROTOR amp ARMATURE SPEED CONTROLLER for MOTORS, MODEL EC613-54 Professional, heavy duty, industrial grade, very high quality Digiac Electrolab motor tester. Functionally in like-new condition. Cosmetically, in very good condition with a few small paint chips. Previously owned by New Mexico State University. This impressive test equipment is great for electronic laboratories, classrooms, science projects (e. g. science fairs), motor demonstrations, and other electronic electrical demonstrations. You can use it to control and demonstrate high-power electric motors from a safe distance. Item is 9-12quot x 9quot x 7quot. UNIQUE ITEM. This is the only one. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 49.95. SH: 10, 10 lbs Used but like-new condition. Tests and demonstrates capacitors. Comes with a 10uF, 236 VAC oil-filled capacitor for power applications. Also comes with banana posts where one can connect in additional capacitors, inductors andresistors, for example, to test power filters and to trim capacitor values. This impressive test equipment can be disassembled (unplug from power first) and the 10 uF capacitor can be disconnected or replaced by some other capacitor(s), inductor(s) andor resistor(s) to suit your particular applications. Sturdy, physically stable device. Professional, heavy duty, industrial grade. Very versatile and useful. Great for electronic laboratories, classrooms, science projects (e. g. science fairs), other electronic electrical demonstrations, etc. Works great and in great condition. UNIQUE ITEM. This is the only one. BUYER: Order by Title (below image) - Email us your order . - List History: LD100. - Price: 29.95. SH: 5, 5 lbs RARE, VINTAGE DIGIAC CORP. ELECTROLAB quotFUSED INPUT CONTROL UNITquot ACDC SWITCH, EC644-05, 250 Volts, 10 Amps Used but like-new condition. Simultaneously controls DC, - DC and AC power inputs to loads up to 250VAC (250 VAC), 250VDC (250 VDC), and 10 A (AC or DC). Professional, heavy duty and industrial grade DC and AC power controller. Sturdy, physically stable device with heavy-duty toggle switch control. Very versatile and useful. This electrical test equipment is great for electronic laboratories, classrooms, science projects (e. g. science fairs), amateur rocketry, amusement park type games, other electronic electrical demonstrations, etc. And by remotely controlling power loads, you can be a safe distance from them with this ACDC power controller, and paying attention to what the loads are doing once powered (as opposed to remotely powering loads by plugging them in). Inputs and outputs each use 4 banana posts, plus one chassis banana post for device chassis earth ground (9 banana posts total). Each inputoutput line is separately fused - you can use any fuse up to 10 Amps. Works great and in great condition. We are not selling this cheap because it is very useful for countless applications - it is worth every dime. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD061, LS092-R25. - Price: 99.95. SH: 6, 6 lbs CDR ROTOR, CORNELL-DUBILIER ELECTRIC CORP. RADIART CORP. for AR-1, AR-2 ROTORS Used, in very good condition, and works fine as we have tested it. Still can be used. We taped a post-it note on the bottom that describes its operation. Bakelite case appears to be in very good condition. Great ham collectible radio collectible electronics collectible. About 6quot wide and long, and 5quot tall. LIMITED QUANTITY. We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD093. - Price: 39.95 Used a few times but in great condition (box is a little worn). With its original documentation. Model 267, Part No. 0509. Pair of test probes are each 12quot long. 50K VOLTS D. C. 20K OhmsVolt. If you have ever been shocked while testing a high-voltage circuit, then you have a clear understanding as to just how critical high voltage probes are for electronic laboratory work we strongly recommend using high-voltage probes for testing all circuits with voltages over 100 volts for all heart-healthy persons, and for much less voltages if you have heart problems or heart pacemaker or any other implanted electronics, as well as to take all other prudent measures to prevent painful shocks and possible electrocution. UNIQUE ITEM - We have only one of this Item. BUYER: Order by Title (below image) - Email us your order . - List History: LD061. - Price: 99.95 HIGH-TECH EXPERIENCED PROFESSIONALISM: Many high-tech businessquot owners and their employees today are clearly woefully ignorant of the high technologies they sell ( including some giant electronic parts houses ). ABQ Techzonics of Albuquerque, NM, USA, is owned by John J. Williams, M. S.E. E. Mr. Williams is a former Senior Electronics Design Engineer ( Lockheed EMSCO ) Professor of Computer Science ( New Mexico State University (NMSU) ) Electronics Weapons Design Engineer ( U. S. Navy, U. S. Air Force ) Health Physicist ( National Institutes of Health (NIH) ), etc. Williams is also currently President of Lone Star Consulting, Inc. and CEO of Consumertronics. net. While we dont know everything about everything tech (no one does), we have a high level of expertise. We sell a lot of electronic components electrical components. Most of these electronic components electrical components are small electronic parts electrical parts, such as integrated circuits, optical devices, transistors, rectifiers, diodes, transformers, inductors, capacitors, resistors, displays, switches, relays, crystals, oscillators, transducers, sensors, prototyping, connectors, fuses, wirecable, power components, etc. as well as some larger electronic parts electrical parts and electronic test equipment, scientific equipment and industrial equipment parts, electrical equipment electronic equipment in general, tools, mounting hardware parts, and special materials. And we also buy and trade these types of items (Trade amp Buy Offers ). And unlike most electrical electronic components sellers, many of the electrical electronic component, etc. lots we buy we set aside some of the electrical electronic parts, etc. for our own electronic projects and research. We sell those electrical electronic parts, etc. we dont use. Our suppliers know that if their electrical electronic parts, electronic test equipment, etc. arent excellent, good chance we will discover it and theyll hear about it ABQ TECHZONICS (Albuquerque, NM) SELLS, BUYS amp TRADES. ELECTRONIC COMPONENTS, ELECTRONIC PARTS, ELECTRICAL COMPONENTS: Integrated Circuits (ICs), Transistors, Diodes, Rectifiers, LEDs, Capacitors, Resistors, Potentiometers (Pots), Varistors, Inductors, Coils, Transformers, Speakers, Relays, Switches, Actuators, Fuses, Circuit Breakers, Thermistors, Crystals, Oscillators, Sensors, Transducers, Optoelectronics, Prototyping, Connectors, Headers, Sockets, Pins, Wires, Cables, Displays, Photo, Video, Laser, RF, Microwave, Electronic Modules, Power Adapters, Power Supplies, other Electronic Parts Electronic Components Electronic Subassemblies Electronic Assemblies. EQUIPMENT, DEVICES: Electronic Test Equipment, Electrical Equipment, Computers, Peripherals, Electric Tools, Hand Tools, Mechanics Tools, Precision Tools, Tool Chests. MORE TECH STUFF: CommercialIndustrialScientificLaboratory Valves, Fittings, Hardware Parts, Mechanical Parts, Supplies, Special Materials, Personal Security, Survival (Survivalists Preppers), Radionics, Crafts, Hobbies, Strange amp Unusual, Religious amp Spiritual, Books, Manuals, Software, Collectibles. SOURCES OF ITEMS ABQ TECHZONICS SELLS: Surplus, online auctions, hamfests, private sales, business moving sales, overstocks, job lots, wholesale lots, estate sales, garage sales, thrift shops, charity auctions, flea markets, hardware trades, abandoned storage, lost amp found property sales, discontinued items, obsolete items, warehouse inventory updates, excess inventories, liquidations, business closures and out-of-business sales, foreclosure sales, bankruptcies, government auctions government sales, new salvage sales, and other sources for integrated circuits (ICs), electronic parts electronic components, hardware, special materials, etc. Albuquerque, NM area preferred but will buy from anywhere. ABQ Techzonics is both a wholesale sellerswholesale traderswholesale buyers and retail sellersretail tradersretail buyers, largely depending on quantity. NOTE: By policy, we never recommend for or against, approve or disapprove, sponsor, endorse, support, guarantee, or take any responsibility for any of the content of any non-Consumertronics webpage, website, advertisement, publication or other statement EVEN IF WE HAVE PROVIDED A HOTLINK TO IT. And by policy, we never recommend for or against, approve or disapprove, sponsor, endorse, support, guarantee, or assume any liability or any other responsibility for any non-Consumertronics company, product or service EVEN IF WE HAVE PROVIDED A HOTLINK TO IT and EVEN IF WE HAVE DISCUSSED IT OR INFORMED YOU ABOUT IT on a webpage, or by phone, email, mail or fax, or by any other means of communications. Everything we sell is sold strictly for legal utility, educational andor entertainment purposes only, and is based on our policies on our policies. htm webpage. Test Source Links only (no visitor use): Source-1, Source-2, Source-3, Source-4, Source-5, Source-6, Source-7, Source-10, Source-11 NOTE: Money Transfer Services (MTS) and all business names referred to on this website (other than ABQ Techzonics and Consumertronics) are referred to only as totally independent sources of services or products our Clients may avail themselves to if they so choose, and to identify the manufacturers of products sold herein (e. g. quotRadio Shack scannerquot). These businesses have identities protected by their own unique trademarks and service marks. We are not in any way agents nor representative of them, nor in business with them (e. g. we are not a MTS, nor outlets nor franchises of them). Nor do we state or imply in any way that these businesses are a part of ABQ Techzonics nor Consumertronics, nor do they endorse nor support any ABQ Techzonics or Consumertronics product, service, policy, activity or operation. Nor do we state or imply in any way that ABQ Techzonics or Consumertronics are a part of these businesses, nor do we endorse nor support any of these businesses products, services, policies, activities or operations. When first introduced, the receiver was the quotHRO. quot No other designation was necessary since it was the only version available. The receiver used nine, 2.5vac heater tubes providing two RF amplifiers, two IF amplifiers, separate Mixer and Local Oscillator functions, a Duplex Diode-Pentode for AVC, Detector and First Audio Amplifier functions, a Beat Frequency Oscillator and a pentode Audio Output Amplifier. The separate power supply utilized a type 80 tube rectifier that actually brought the tube total to ten. Typical of most communications receiver manufacturing, progressively later models will have several minor improvements added as production continued. During early production both rack mounted versions with 316quot thick aluminum panels finished in a textured quotcrackle finishquot that resembled leatherette were produced along with the standard table model that was painted with standard wrinkle finish. Its likely National anticipated that a large number of the initial orders for the HRO would be from commercial users and thus many of the first production run receivers were the rack mount variety. In fact, 60 of the reported serial numbers to WHRM that are quotfirst production runquot HRO receivers are from rack mount receivers (see Serial Number Log in section below.) A specific power supply wasnt available for the early HRO receivers, so many receivers were sold with the FB-7 power supply, type 5897AB with the data plate emblazoned quotDesigned Especially for the FB-7.quot Many rack mounted power supplies were also produced for the commercial users. Speakers were not specifically available in a table cabinet but National advertising stated that a quotloud speaker could be provided, if desired. quot The first advertised speaker shown was a rack mount version. Shown in the photo to the right is a rack mount HRO from the first production run with the serial number of D-65. Note that this receiver has all of the features that are found on the earliest production. D-65 has the pearl-button push switch for the S-meter and the small red quotNCquot dial pointer mounting screw. Also obvious are the white background frequency charts on the coil sets. Notable is the leatherette finish on the panel and on the coil set panels, although this finish was used on the rack mounted receiver up until around 1940. This receiver was probably built around January or February of 1935. photo above: HRO sn: D-65 (rack mount,) first production run built in January 1935 photo above: HRO sn: H-103 (table cabinet) was built in September 1935 (5th production run.) The quotHquot production run was the last to use the plated PW-D, the 0-5 scale S-meter (later 0-5 scale) and the early-style cabinet. Compare D-65 from the first production run to fifth production run receiver, H-103, shown in the photo to the left. H-103 is a table model rather than a rack mount so it has the standard black wrinkle finish. H-103 has several production upgrades incorporated with the most noticeable being the black push-pull S-meter switch that replaced the pearl-button switch after the second production run. The original push-button was inconvenient to use and also was noisy in operation. Also apparent is the pilot lamp. It was noted that there was no visual indication that the receiver powered-up so the pilot lamp had to be added by the third run. The frequency charts became black background after the middle of the third run. Moisture may have caused staining on the white charts that prompted the change to black charts. Internally, a Remote Standby had been added and there was an improvement to the plug-in coil contacts. The sixth production run, run-J, would bring several changes to the HRO. Gone would be the plated PW-D dial in favor of a lacquer painted version. The cabinet would also now feature improved ventilation with louvers on the side and enlarged holes on the rear. The S-meter scale was changed from the old QSA 0-5 scaling to the RST scaling of 0-9. These quotJ-runquot receivers were advertised as the quot1936quot HRO. The HROs design was much more advanced than any other communications receiver available in early 1935. James Millen, using his monthly QST letter to hams, had the ham interest piqued and both commercial users and hams rushed to buy the first HRO production available. Of course, the HRO performance became legend quickly and, if the receiver was affordable to a depression-era enthusiast, it was purchased. The production runs were very small and by the introduction of the HRO Senior in 1936, about 1100 HROs had been produced and sold. Features Found on the Earliest HRO Receivers - Shown below are some of the external parts and manufacturing variations that are found only on the early HRO receivers, that is, the receivers built in 1935. Photo quotAquot shows the German Silver plated Micrometer dial. This dial was used for the first five production runs (D, E, F, G amp H.) Photo quotBquot shows the quotNCquot emblem that is used with the dial pointer. This emblem was exclusively used on the initial production run (run-D.) It was then used for most of run-E and sporadically on runs-F and G alternating with the quotdiamondquot emblem (see HRO Senior below for close-up photo.) Photo quotCquot shows the pearl push-button S-meter switch that was used only for two production runs, runs-D and E, along with the quotraised-rounded flangequot S-meter only used for the E-run. Additionally, the S-meter shown has the early 0-5 S-Units scaling that was used on runs D amp E. By run F, the quotPLUSquot was dropped and the NC diamond was changed to red with black quotNC. quot Photo quotDquot shows the white background frequency graphs that were used for three production runs, runs-D, E and F. Photo quotEquot shows a small dial-knob with the short boss (left) used on run-D through part of run-J. The small dial-knob to the right has the taller boss used from production run-J-on. Photo quotFquot shows the black painted chassis that was found on production runs-D through L. This photo also shows the round IF and BFO shields (cans) that was used from runs-D through P. Photo quotGquot shows the early cabinet ventilation holes that were used from production run-D through J. (photos B and C are by Gary Halverson K6GLH of his HRO SN: E-159) The HRO was an expensive receiver, priced at about 200 with all of the accessories necessary for operation. In the January 1936 issue of QST, James Millen indicated that he had been in contact with many hams who were HRO owners - either through letters or actual visits to their ham stations. He came to the conclusion that most hams didnt use the HRO to its full capabilities. Most hams never used the Crystal Filter. Many never switched the coil sets to amateur bandspread. Most hams were on CW at that time and never used the S-meter. Millen also indicated that some letters from hams actually inquired if they could order the HRO - minus specific circuits they believed they wouldnt need - at a reduced price, of course. Millen thought that offering a budget priced HRO, that eliminated these unused circuits and parts might be a good seller. Certainly, it would be a way for the Depression Era ham on a strictly limited budget to get an HRO. National announced the reduced-cost HRO in February 1936, dubbed quotHRO Junior. quot From that point on, the standard HRO became known as the quotHRO Senior. quot The HRO Junior didnt have a crystal filter. This modification required that the Crystal Filter assembly be replaced with a standard IF transformer. Elimination of the S-meter also eliminated the meter push-pull switch and meter adjustment pot circuitry. photo right: HRO Junior sn P-116 from August 1936 with its original P-116 JD coil set installed. Note that this receiver has a gun-metal gray lacquer on the PW-D micrometer dial. Some PW-D dials will have a dark bronze color lacquer paint. Note that the pilot lamp location is different than the HRO Senior. Also, the location of the phone jack is moved since there is no S-meter switch (or S-meter.) Also obvious is the centrally located frequency graph on the coil set. Since the Junior coils didnt bandspread only one graph was necessary. Naturally, a different front panel was going to be required since the meter wasnt used. National also moved the location of the pilot lamp slightly to the right and moved the phone jack slightly to the left. The Junior used the same chassis as the regular HRO, obvious because the S-meter pot mounting hole is present as are the mounting holes for the Crystal Filter assembly. The coil sets for the quotJuniorquot did not have the bandspread feature and were identified with a quotJquot proceeding the regular coil set letter designator. Since quotJquot coils couldnt be set to bandspread only one tuning chart was needed and it was centrally mounted on the coil panel. The quotJuniorquot was usually offered for 99 from most of the discount dealers but this price only included one coil set. Millen recommended equipping the quotJuniorquot with two coils sets, the JA and the JC for the CW operator giving coverage of 20 and 10 meters on the JA coil and 40 and 80 meters on the JC coil. For the AM phone op, the JA and JD coils gave 160 and 80 meters (JD) and 20 and 10 meters (JA) - at that time (pre-WWII) 40 meters was a CW only band. Of course, a purchaser could order as many coils as they wanted although the idea of the Junior was to keep the cost down by utilizing only what was going to be absolutely necessary. photo left . The chassis of HRO Junior P-116 showing the absence of the Crystal Filter and S-meter. Note that the chassis is punched for the S-meter adjustment pot which was located next to the Antenna-Ground terminal insulator. This Junior has the gray chassis paint which started to be used in early 1936. The IF cans had just changed to the square type with the quotPquot production run. The HRO Junior was not a quotreduced costquot HRO in the sense that it would have been built using cheaper parts. Rather, the Junior used all of the standard Senior parts and assembly techniques - just the S-meter, the Crystal Filter and the bandspreading coil sets were not used. The cost was less than the standard HRO because certain circuits and parts were not used - circuitry and parts that some hams or other users might find superfluous to their needs. Since the Junior had almost everything a Senior had it was natural that National offered to upgrade a Junior after purchase (at a later date - perhaps when the owner had saved up the money) for a very reasonable price. Perhaps some Juniors were sent back to National for conversion to an HRO Senior though there doesnt seem to be much evidence that it happened too often. A new front panel would have been required along with the Crystal Filter assembly and S-meter with the S-meter switch. Then there was the problem of the J coil sets. Although the conversion was offered, it must have been done at a quotlossquot for National, who probably realized that very few Juniors would ever be returned for the conversion to Seniors. The HRO Junior wasnt very popular and today it is quite a rare set in its original configuration. Most thirties-era hams probably realized that purchasing the Junior wasnt that good of a quotdeal. quot The HRO Senior was around 170 with four bandspreading coil sets included. Most dealers would sell the HRO Senior with some money down and monthly payments to follow. The Junior was 99 with one general coverage coil set. Just adding the three coil sets to provide full frequency coverage would run the price up to about 150 and then these coils would not bandspread. The price would be even more if bandspreading coils were desired. For only a few dollars more, the HRO Senior provided many more features. Power supplies and speakers were considered extra accessories for both types of receivers. Most quotJuniorsquot encountered today are really RAS or RBJ Navy receivers - rack mounted HRO Juniors with some modifications for military use. Like Millen had observed with the hams, the Navy found their radio operators had little use for an S-meter, Crystal Filter or Bandspread coil sets. Apparently, American Airlines also felt the Junior was more of what they wanted and some rack mount HRO Juniors were supplied to them. These HRO Juniors are identified with double quotAAquot preceding the HRO, i. e. AA-HRO. photo above: 1936 advertisement for the Juniors introduction. From February 1936 on - coinciding with the HRO Junior introduction - the standard HRO was referred to as the quotHRO Senior. quot From this point up to just before the WWII, the HRO went through several minor physical changes. Most noticeable came in late-1935. This was the change from the German Silver plated PW-D micrometer dial to a black lacquer dial. The black paint color on the PW-D micrometer dials varies from dark gunmetal gray to dark bronze. There doesnt seem to be any chronology to the variability of the subtle shading which indicates that the paint mix variability was just part of the production process at National. Under intense light the PW-D will show its true color shading (as in the photos shown) but in normal room illumination most of the paint shadings appear black. The inner dial readout also changed from black numerals on silver to white numerals on black paint. The cost savings were realized by Doehler (the manufacturer of the PW-D) in that they could now use castings that had pits and other defects that would be quotfilledquot by the lacquer paint. Also, since the index lines were going to be filled with paint, they were widened slightly so the paint fill would appear the correct width when finished (the earliest painted dials had the narrow index lines.) Other changes were to the chassis color, probably to conform with the gray paint that was being used used on the new 1936 NC-100 receivers. This cost savings was realized in that only the small quantity SW-3 receivers continued to have the black chassis paint. Starting in January 1936, most of production now used gray paint for all chassis. By mid-1936, the IF transformers were changed to different adjusting screws with slots instead of hex heads and the shields were changed to square rather than the earlier round shields. Again, the cost savings was that the the HRO would conform with the NC-100 series, although better quality IF transformers were probably also involved in the changeover. gtgtgt photo above . HRO Senior sn: N-130 was built in July 1936 and has the features found in the early HRO Seniors. Most noticeable is the bakelite housing, white face S-meter (that is non-illuminated on early versions) and the painted PW-D. Note that the paint on this PW-D is the dark gunmetal gray lacquer. gtgtgt In the December 1936 issue of QST, National ran an ad on the back-inside cover showing a rack mount HRO finished in gray quotleatherettequot finish. The photo below shows a table rack designated MRR and a combination speaker and coil storage box designated SPC. The ad states that the rack mount HRO is available, quotYour choice of finish, either rich grey or black leatherette. quot (note the British spelling of gray.) A close-up of the receiver shown in the ad below. This ad ran several times in QST from 1936 up to around 1938. Note the bound QST magazines on the book shelf. Besides this advertised color option, HRO receivers have been found with original paint in blue (special orders to RCAF Canada) and smooth machine grayish-blue (possibly other Canadian users.) Other colors probably exist since National would do special orders and had the in-factory paint facilities. Another minor change at the time was to the remote standby terminals which now placed the quotBSWquot terminals in series with the panel B switch requiring a jumper be installed across the terminals if the receiver was used without a remote T-R switch. This seemingly minor change actually now provided the operator of a transmit-receive station the ability to remove the B independent of the T-R switch - a function required for safe coil set removal and installation. The S-meter had been a Marion Electric Instrument Company bakelite housing meter with a non-illuminated white scale with 0-9 S-units in black and the NC diamond in red. By 1937, this S-meter became an illuminated meter. The next change (early 1938 - possibly by run-W) was to an illuminated light-yellow scaled meter. The S-meter also added quotdb above S-9quot to the scale in red printing. gtgtgt photo above . Gray HRO Rack Mount from 1936 QST Advertisement gtgtgt Finally, an identification tag was added to the upper right corner of the front panel in late-1938. This was the first time that the actual receiver model is physically identified in any manner. This completed the physical evolution of the HRO from 1936 to 1938. From then up to WWII, the HRO looked the same except that some very late HRO Seniors will have a bar knob for the selectivity adjustment. By the later thirties, most of the HRO receivers were being equipped with 6.3vac tubes. One of Millens QST letters (1937) had pointed out that the 2.5vac heater tubes were preferred by National since the 6.3vac heater tube were subject to producing modulated hum. In 1939, the 697 power supply was introduced featuring a 6.3vac heater winding with sufficient current to operate the HRO and packaged in the quotdog housequot style cabinet. At this time, the older 2.5vac tubes were all but eliminated from the production HRO receiver. Millen also recanted his former opinion of the 6.3vac tubes in 1939, when the 697 power supply became available. There was some speculation by former National employees that the actual reason for the preference for 2.5vac tubes was that National had over-stocked the 2.5vac filament winding HRO-type power transformers and these really werent useable anywhere else. The story goes that National kept up the 2.5vac tube performance quotmythquot active until they depleted their over-stocked transformers. Many HRO owners did re-tube their older 2.5vac HRO receivers with 6.3vac tubes. More than likely this was due to tube availability rather than performance improvement. About this time, May 1939, James Millen resigned from National. The reason sited at the time was so Millen could form James Millen Manufacturing Company but other factors may have been involved. See quotHRO Production amp Engineering Changesquot section (1939) below for several various reasons sited for Millens departure from National. photo above: HRO Senior sn: 463-K was built in 1940 and has most of the quotlate pre-warquot HRO Senior characteristics. Most noticeable is the illuminated S-meter with amber scale (these scales were originally a light yellow color but darken due to exposure to UV or bright light.) Also note the name plate in the upper right of the panel and the PW-D that has the dark bronze paint. Features Found on Later Pre-War HRO Senior Receivers - Probably the most obvious difference between the early HRO receivers and the later HRO Senior is the lacquer finished micrometer dial that made its appearance with production run-J (1936). The painted micrometer dials are shown in photo A and B . Photo A shows the gunmetal gray lacquer and Photo B shows the dark bronze lacquer. Photo C shows the early bakelite housing S-meter that is non-illuminated at first but later was illuminated and has the S-9 scale on a white meter face. These meters were being installed by run-J and are used up to around run-W (early 1938.) Photo D shows the later Marion Electric bakelite illuminated S-meter that was installed beginning with run-W (early 1938.) Typical of the later Marion S-meters, this example shows considerable fading of the red scale, quotDB OVER S-9quot and the scale face itself has darkened somewhat from the original light-yellow color. Also, note that this photo shows the black pull-switch that replaced the pearl push-button with run-F (1935.) Photo E shows the quotraised diamondquot pointer-mounting screw that started to replace the quotNCquot emblem mounting screw as early as production run-E (1935) but was intermixed with the quotNCquot emblem until run-H. Photo F shows the black background coil frequency graphs that were installed during the latter part of the third production run (run-F.) Photo G shows the improved ventilation of the new cabinet introduced with run-J (1936.) Photo H shows the early gray painted chassis with round IF-BFO cans and the fiber board Antenna-Ground terminal mount (gray paint beginning run-L, 1936.) Photo I shows the later gray chassis with square IF and BFO cans (square cans beginning run-P.) Also, note in Photo I the polystyrene Antenna-Ground terminal mount which was introduced very late in production, around run-suffix F (1939.) Note: photos A, C and H are of N-130 (1936). Photos B, D, E, F, G and I are of 463-K (1940.) The HRO During WWII Prior to WWII, the Navy was buying some HRO receivers for various uses. These receivers generally will have a National Audio Output transformer installed in the chassis area behind the S-meter and adjacent to the antenna terminals. This area of the standard chassis already had mounting holes and lead thru holes for an audio transformer, implying that National anticipated some customers requiring this option. This would especially be true for many commercial users as well as the military. In fact, some National catalogs do mention that any audio output configuration could be provided. The Navy wanted 500 ohm Z outputs for their requirements and the National transformer usually installed is a National Type S500. Also, these pre-WWII Navy HROs will usually have an quotanchorquot ink stamped somewhere around the chassis or chassis mounted parts. Other than the audio configuration changes, the pre-WWII Navy HROs are standard production types and even have the standard serial number placement and format which implies that the Navy purchased them quotas neededquot rather than by a large quantity contract. Perhaps the HROs most famous use during WWII was in England where banks of HROs were set-up as intercept receivers at various sites. Generally, most reception stations were separated from the transmitting sites and the decoding sites were separate from either the reception or transmitting sites. At first, Britain couldnt buy the HRO receivers directly, so various methods were used to purchase the receivers. Usually, British officials in the US on business would purchase an HRO receiver from a dealer and hand carry it back to England. This rather tedious method lasted until Lend-Lease was passed at which time then the British were able to have a steady supply of HROs direct from National. Many of the HROs sent via Lend-Lease were identified with a double letter prefix to the serial number, e. g. PP or AJ, etc. It also appears that single quotPquot prefixes with numbers above 150 seemed to indicate HROs destined for duty overseas. The HRO-M amp HRO-MX - The HRO Senior was given a few engineering upgrades at the end of 1941 or early in 1942. The most obvious was the modification of the crystal filter to use an internally mounted crystal, thus eliminating the quoteasy to removequot crystal that plugged into the top of the filter assembly. There was always questions that arouse regarding the plug-in crystal in that the quotair gapquot required for the crystal seemed to be interpreted as something quotloosequot and quotrattling aroundquot in the crystal. The new design crystal eliminated that unwarranted concern and didnt change how the Crystal Filter operated. After that change, National referred to the new HRO Senior as the HRO-M or MX. During WWII, the HRO-M was improved with ID rings added to the AVC and B toggle switches. Many HRO-M receivers will have a 0-1mA scaled S-meter made by Marion Electric. Initially, these mA meters were only for the receivers being sent to England but later many military HROs had this meter installed. The S-meter quotpull-switchquot was replaced with a black-finish, ball-handle toggle switch. photo right: Inspection tag from WWII HRO-M sn PP-988 showing the various signatures and dates for the operations to complete the receiver. The HRO-M is owned by G3UWP - Robin Pickering, who found the tag wedged between the chassis and the cabinet of the receiver. Full dates show June 30, 1943 photo above . The U. S. Navy RBJ-2 receiver featured 50kc to 400kc and 480kc to 30mc coverage with nine coil sets. The RAS, RBJ amp RAW, etc. - The U. S. Navy wanted a simple to use receiver and National supplied HRO Juniors in fairly large numbers as the RBJ, RAW and the RAS (possibly other designations were also used.) The RAS was a special receiver that had a 175KC IF to allow tuning through 400KC to 500KC range without interruption. The lower end of the frequency coverage was 190kc. The RAS models also have special coil sets for 175KC IF operation and are identified with a special number code. The RBJ individual coils (four in each coil set) are also apparently different than the standard HRO because National assigned them a different number code. The Navy receivers were normally rack mounted and usually were supplied with anywhere from five to nine coil sets that were housed in a coil storage box that was rack mounted. The RAS came with seven coil sets while the RBJ was supplied with nine. Unlike the HRO which used letters to ID the coil sets, the RAS and RBJ used a number ID, 1 to 7 for the RAS and 1 to 9 for the RBJ. The power supply was a rack mounted type and the power cable from the receiver was a shielded cable (even though cloth covered.) Loud speaker panels were generally not included in the rack since nearly all Navy operations required headset reception by the radioman. During the RBJ, RAW and RAS production the plug-in coil set panels were changed from 316quot thick aluminum to 18quot steel panels. Small ID tags are mounted between the frequency graph and the logging chart for coil identification. In fact, all of the Navy HRO receivers have a multitude of data plates on the coil box, the power supply, the receiver and each coil set. Unfortunately, over the years many of these Navy HROs have been stripped of their data plates making actual identification somewhat difficult without a close inspection. photo above: The U. S. Coast Guard version of the HRO Senior was designated as the RC-105 and the matching loudspeaker was designated as the R-115. The set shown belongs to Brian KN4R who supplied the photograph. Other Designations - The U. S. Coast Guard also purchased HRO receivers with designations of RC-105. These are HRO Seniors and probably date to shortly before WWII and into the beginning of WWII. Additionally, the British designated some of their HRO-M receivers as R-106. To further add to the confusion, the U. S. Army Signal Corps also identified some of their HRO-M receivers as R-106. The Signal Corps versions have a specific data plate mounted in the upper right corner of the panel. There was an HRO-12-S that operated on a 12vdc battery system with the 1286 power pack which may have been built for Canadian use. The U. S. Navy also had the RDG which was a scanning receiver that interfaced with a panadapter. The RDG used plug-in coil sets that are identical to the HRO (even using the same individual coil identification numbers.) There are certainly many more designations and variations. During WWII, the many variations of the HRO and its accessories were necessary for the various uses the receiver was put to and for the various end-users of the receiver. Some end-users modified their HRO receivers to their specific needs and these receivers were sometimes given new designations. The HRO-5 amp HRO-W - Near the end of WWII, the HRO was upgraded to all octal metal tubes (except the 6V6GT quotglassquot audio tube) and most of the components became JAN standard values. This receiver was dubbed the HRO-5. The HRO-5 was identified as HRO-W if it was going specifically to the Signal Corps. They are virtually the same receivers. The HRO-W will have a military data plate installed in the upper right corner of the panel that specifically identifies the receiver as quotHRO-Wquot and the contract number is quot49906-PHILA-45-03.quot The HRO-5W receivers generally have a Marion Electric S-meter that is non-illuminated and has a white metal 0 to 1.0mA scale. The National manual is not very specific about the S-meter and some HRO-5W receivers have turned up with the standard amber S-meter scale installed. The common belief was that the all white scale mA meters were exported to England but there were many exceptions to this and the HRO-W is commonly found with the mA meter. Additionally, the S-meter ball-handle toggle switch was replaced with a quotbat handlequot toggle switch. The HRO-5W cabinet was changed to have no ventilation holes in the rear panel of the cabinet or louvers on the sides. The HRO-5W was sometimes powered by the 697W heavy duty power supply. Sometimes receivers were given a heavy moisture and fungus proofing for severe service depending on the intended location. Audio output transformers are shown as optional for the HRO-5 in the National manual but are shown on the HRO-5 schematic. The HRO-W didnt have an audio output transformer installed in the receiver. With the HRO-5W, coil sets were changed to have a large aluminum plate with silk-screened frequency graph and logging chart along with the coil set identification mounted onto the front panel of the coil set. All HRO-W receivers reported so far are from the WWII quotKquot production run in 1945. All HRO-5 receivers appear to be from the WWII quotJquot production run in 1945. photos leftamp below . The Signal Corps version, the HRO-W sn: K-127, from mid-1945. All HRO-W receivers were heavily coated with MFP which is a yellow lacquer with a fungicide added. Even the knobs are MFDd. Note the gold appearance of the knob skirts and the olive drab appearance of the PW-D dial which is due to the heavy MFP coating. Under the lid is silk-screened data with a place for stamping an application date. In this receivers case, the date is JUL 29, 1945. Also note the use of metal octal tubes that began with the HRO-5W receivers, the non-ventilated cabinet and the silk-screened coil ID plate. HRO Copies from Other Countries - National Co. Inc. published a pamphlet in 1964 that celebrated their 50th anniversary in business. Inside that pamphlet, National mentioned that both Germany and Japan had produced quotknock-offsquot of the HRO. Shown in one of the photos in the pamphlet was a technician testing one of the German HRO copies. Also shown was one of the Japanese copies. Both photos are shown below. The Germans built at least two HRO copies during WWII, the Korting KST and the Siemens R4. After WWII, a few other copies were built in Eastern Germany. Later versions of the East German copy used Czech tubes and Russian resistors. photo left: A National engineer testing one of the WWII German copies of the HRO. Note the HRO-5 receiver to the left of the German HRO. Also, note the incredibly huge General Radio 805-C Signal Generator being adjusted. photo right: A Japanese copy of the HRO from WWII. Note that the nomenclature is entirely in Japanese. These copies were not as quotliteralquot as the German copies. Both photos are from quotNationals Anniversary Photo Albumquot - published in 1964 for Nationals fifty years 1914-1964 in business. Kingsley Radio Company - AR7 - In addition to Axis-created copies of the HRO, some of our allies also created quotknock-offs. quot Probably the best known HRO quotknock-offquot is the AR7 receiver built during WWII by Kingsley Radio Co. of Melbourne, Australia. The Australian Army referred to the AR7 as quotReception Set No.1quot while Kingsleys original designation was KCR11. Though the AR7 has a micrometer dial and uses plug-in coil sets, thats about as far as the HRO copying went. The AR7 uses eight tubes (plus two in the original PS) and covers 138kc up to 25mc using five coil sets. Rather than using a separate Mixer and Local Oscillator, the AR7 uses a Converter Stage. The tubes employed are standard quotAmericanquot tube types. The receiver uses a stainless steel overlay on the front panel although some of the Australia Army receivers have the front panels painted green. Interestingly, the S-meter on the AR7 works quotbackwards. quot Full scale is quot0quot and mechanical zero is quot9.quot Additionally, the micrometer dial also works quotbackwardsquot (when compared to the HRO) with 0 being the highest frequency tuned and 500 being the lowest. All AR7 receivers were rack mounted with a rack mounted power supply and a rack mounted speaker. The audio output impedance was approximately 1750 Z ohms and 600 Z ohms and the panel jacks provided both audio outputs. Probably around 3000 AR7s were produced. After WWII, the AR7 was used extensively in airports around Australia as a communications receiver. Some of the receivers had the LO coil removed from the coil sets and a Crystal controlled oscillator installed for quotfixed frequencyquot operation. It was common to find quotbanksquot of modified AR7s in Australian airports post-WWII. See quotCollectors Galleryquot below for the Amalgamated Wireless Australasia AMR-100 quotHRO Copyquot from K6DGH. photo right . Kingsley Radio Co. Melbourne, Australia - AR-7 receiver. Most receivers left the stainless steel front panel overlay unpainted with the nomenclature slightly polished to improve its readability. Note that the coil graphs are also stamped stainless overlays. Two graphs are used to improve the accuracy of the graph. The coil sets are general coverage only. HRO-5A, HRO-5A1 and HRO-6 At the end of WWII, almost all manufacturing had been for the war effort since 1942. Most companies were ready to start civilian production by September 1945. National, like most other radio companies, offered what had been late WWII receivers as the initial, post-war product line. The first post-WWII receivers offered were standard WWII HRO-5W models with general coverage coils and a aluminum silk-screened panel with graphs and ID mounted to the coil assembly. These coils sets will be IDd as JA, JB, etc. to indicate they are general coverage only. Since the military HRO-5W came with nine coil sets, this may have been offered with the civilian HRO-5W (at an extra cost.) Its also likely that some of the civilian HRO-5W power supplies were the heavy duty 697W. See 1946 Radio Shack Boston ad below showing the HRO-W being offered for 217.35 including power supply and four coil sets. Note that the other five coils sets are offered at an extra cost. No wonder its so hard to find an HRO-W with its complete original nine coil sets. Additionally, the power supply shown in the ads artwork is the standard 697 and not the heavy-duty quotWquot version. As expected, the coils sets are quotJquot version non-bandspreading types. Note that the meter shown is the 0-1mA Marion Electric that was standard for the HRO-W. Updates from National seem to come at a leisurely pace and by early 1946 the HRO-5 had been upgraded to have the A, B,C and D coils feature the bandspread function. National designated this receiver the HRO-5A. National replaced the white scale 0-1mA scaled meter used in the HRO-5W with the round S meter with yellow-amber scale made by Marion Electric (as used on the pre-war HRO Senior) although some HROs were also fitted with a white S meter scale with the quotNCquot diamond logo (probably left-over stock from earlier manufacturing.) photo above . The HRO-5TA1 sn: 184 1054. This is a very late version of the receiver (made well after June 1946) featuring the square S-meter made by Marion Electric which was used to conform with the S-meter used on the NC-240D receiver. Also, this receiver has the later cadmium-plated chassis and the six-step Selectivity control for the Crystal Filter operation. Note the increased spacing between the two Crystal Filter controls. The HRO-5A1 was introduced around March 1946 although this receiver is still basically built from mostly quotleft-overquot stock. The 5A1 featured a Noise Limiter circuit that added two more tubes to the receiver bringing the total to twelve tubes. There was no ideal place to add the Noise Limiter control so National mounted it about the only place there was room for it - to the left of the PW-D dial. The Noise Limiter potentiometer somewhat blocks easy accessibility to the 1RF adjustments when performing an alignment. The NL circuit is built onto a small chassis on these early receivers. The hum resistor on the tube heaters was eliminated and instead one side of the heater line was connected to the chassis. Typically, the National ID plate is mounted over the NL control. Many of these early versions are MFP coated for some reason. On all HRO receivers built between September 1945 up to about June of 1946, its apparent that National was trying to clear out any of the old stock along with the WWII stock and just about anything they thought they could put into a receiver and successfully sell it. National had two warehouses in the Malden area with lots of quotleft-over stockquot to work through. Consequently, any HRO-5, HRO-5A or HRO-5A1 made in that time period is likely to have parts that seem to come from either different receivers or a different time period. Its difficult to list all of the variations that could be possible. Just suffice it to say that just about any combination of parts are likely to be found on the HRO receivers built between September 1945 and June 1946. These early HRO-5A1 receivers were offered up to July1946. photo left: This is a 1946 Radio Shack Boston advertisement showing the HRO-W for sale with power supply and only four coil sets included. Note that the remaining five coil sets would cost extra. Also note that these are the military quotJquot coils as would be expected immediately after WWII. Another note is that the power supply shown in the ad is the standard 697 type. Ad copy provided by: Michael Everett photo right . This is an early HRO-5TA1 from March 1946 showing that at this time National was still using the round Marion Electric S-meter and quotleft-overquot HRO-W front panels. Note that the ID tag is over the Noise Limiter and there are mounting holes in the upper right corner for the HRO-W data plate. This receiver also has the small chassis NL circuit and for some reason is MFP coated. photo: from eBay The photos to the right show an HRO-5TA1 probably built around April or May of 1946. Although this receiver appears to have the National tag installed back in its proper place in the upper right corner of the front panel, note that the S-meter scale is an earlier style scale from pre-WWII but it is installed in the typical WWII Marion bakelite meter case. Note on this version that the Crystal Filter is still the older style with the close spacing of the two small dials and with the Selectivity control as the upper dial. Looking at the photo far right of the chassis it is obvious that this receiver is still using WWII quotleft-oversquot in the IF transformers and BFO coils. Note that the last IF transformer shield and the BFO coil shield are MFPd. The BFO coil shield still has the WWII ID printing on it. Also apparent is the gray painted chassis. gtgtgt photos right . from eBay gtgtgt Though difficult to tell, the Noise Limiter is still being built onto a small chassis mounted on top of the main chassis. Note the cable routed across the chassis going to the NL chassis. The cable exits the chassis to the right of the 6V6 audio output tube. A new version of the HRO-5TA1 was introduced around July, 1946. It featured a new Noise Limiter circuit that was now built onto the receiver chassis which was now cadmium-plated. At the same time, the Crystal Filter was changed to a more conventional circuit that National had used on the WWII NC-100XA series (RAO USN receivers) with a six position switch controlling Selectivity and a variable capacitor to adjust Phasing. The position of the two controls were interchanged and the spacing between the two controls increased when compared to the earlier HRO Crystal Filter. Another change was to the S-meter which became a Marion Electric meter with a square housing (to conform with the meter used on the new NC-240D.) Additionally, on the later HRO-5A1 receivers the serial number format is changed from the old letter designation for production run identification to a three digit number identification. The specific receiver is identified with a four digit number which results in a seven digit serial number that was then relocated to the rightside of the chassis about midway back. Although dealers began offering the newer version HRO-5A1 as early as July 1946, National didnt feature it on a back cover ad in QST until February 1947. The construction of these later HRO-5A1 receivers is very consistent and will use all new parts in the assembly. photo right . Inside a very late version HRO-5TA1 (sn: 184-1054) showing that the chassis is now cadmium plated (post-July 46 units,) two more tubes are added next to the left side of the tuning condenser for the chassis mounted Noise Limiter. Also, note the NATIONAL decal has returned and is installed under the lid. These decals began to be installed on cabinets very early in production - by run-G (1935) but were not applied to the cabinets during WWII. Also, note rear wall of cabinet has no ventilation holes as the pre-WWII HRO Senior cabinets did. HRO-6 - Are the Late HRO-5TA1 Receivers Actually HRO-6s - In late-1946 or early 1947, a short lived HRO-6 was produced with an quotimprovedquot Noise Limiter but its physical appearance is identical to the HRO-5A1. Some National manuals will have an advertisement in the back pages for the HRO-6. These ads date from 1946. Very few HRO-6 models were sold and it is seldom encountered today. Its known that HRO-6 receivers were built with-in the same production run as some late versions of the HRO-5TA1 receivers. Note in the quotHRO Serial Number Logquot (below) that the two HRO-6 and five of the HRO-5TA-1 receivers are all from run 184. Interestingly, three of the HRO-5TA-1 receivers (one of which is the quotvery latequot HRO-5TA1 shown in the photos above) are apparently a higher serial numbers than the highest reported HRO-6 serial number. It appears that for a very short period of time, during the middle of run 184, the HRO-6 designation was used on only a small quantity of receivers. The HRO-6 serial numbers seem to be inter-mixed with HRO-5A-1 serial numbers. It might be possible that National considered identifying the later, post-July 1946 HRO-5A1 receivers as the quotHRO-6quot since these late HRO-5A1 receivers incorporated so many changes when compared to the HRO-5, HRO-5A and the highly variable (construction-wise) early versions of the HRO-5A1 receivers. In comparing photographs of the HRO-6 to the late version HRO-5A1, there are no apparent differences and perhaps only the ID tag is the sole change. Perhaps the quotimprovedquot NL was the fact that these quotlatequot HRO-5A1 receivers had the NL built onto the chassis rather than the separate small NL chassis used in early HRO-5A1 production. National may have quotjumped the gunquot on the HRO-6 designation since basically the post-July 1946 HRO-5TA1 (or HRO-6) looked very much like all of the proceeding HRO models. National had certainly started design work on the HRO-7 which was going to have significant changes to its external appearance, fitting a new model receiver designed after WWII. Maybe to keep the quotolderquot looking HRO-6 from being mistaken for Nationals quotnew post-WWII design, quot the designation of HRO-6 was quickly dropped and returned to HRO-5TA1. National didnt want the late-1946 (1947 model year) prospective customers to think that National was still just quotrevampingquot the old HRO as their new model receiver. By stopping the HRO-6 designation, the introduction of the HRO-7 would then have been seen as Nationals quotnew post-WWII designquot and that their quotnewquot receiver would have a quotnewquot look, completely different from the older HRO receivers. For the 1947 model year a complete quotmake-overquot was given to the old HRO. Introduced in mid-1947, the HRO-7 had a new cabinet with slightly rounded corners, a smooth light-gray paint job, levers for easy coil removal, S-meter viewed though a panel quotcut-out, quot different knobs with light gray grips, a light gray PW-D. however, the HRO-7 circuit remained basically the same as the early HRO-5TA1. There were some tube changes and a tube addition with the local oscillator changed to a miniature tube (6C4) and an added voltage regulator (0A2) but the HRO-7 was really not much more than a cosmetic upgrade. Its introduction did spell the end of the rectangular, black wrinkle finish box though. The HROs exterior had remained basically unchanged for the past 12 years. The HRO-7 was also offered in a rack mount configuration called the HRO-7R and it was very different from the table model with black wrinkle finish panel, external S-meter mounting, a black PW-D and different knobs. Generally, the rack included a coil storage unit and a rack mounted speaker. The HRO-7 was available for about three years but Nationals next upgrade was going to change almost everything about the old HRO receiver. photo above: 1948 advertising artwork for the National HRO-7, note that the speaker style was also changed to a more quotmodernquot look. HRO-50, HRO-50-1 and HRO-60 photo above: HRO-50T from 1950. Note the gray plastic grips on the smaller knobs while the PW-D is sporting the black HRK-style knob. Earliest receivers had a gray HRT-style knob on the PW-D. This HRO-50T is SN 280-0194 The HRO-50 and HRO 50-1 - The new HRO-50 was going to bring the HRO design into the mid-twentieth century. The separate power supply was first on the list of things that needed to go. The new HRO power supply was built-in though on a separate chassis that was bolted behind the main receiver chassis and thermally insulated from the receiver chassis by an asbestos sheet that was also continued up to the top of the vertical divider panel to provide insulation from the heat from the rectifier tube and the audio tubes. Relying on the micrometer dial versus graphs was also gone. Now an illuminated linear slide-rule dial would provide direct frequency readout. Changeable plastic scales were mounted to a front panel controlled, rotating drum, providing band-in-use scaling. The PW-D dial was now just for logging purposes. An Antenna Trim control on the front panel was finally incorporated. Auxiliary sockets were provided for the optional 1MC100KC crystal calibrator and NBFM adaptor. Also, a Local Oscillator Trim that allowed front panel calibration for the best dial accuracy (using the crystal calibrator - either the optional one or an external calibrator.) Voltage regulator, push-pull audio, 8Z ohm and 500Z ohm audio outputs - almost everything necessary to update the old HRO. The plug-in coils had to remain along with the PW-D micrometer dial otherwise it wouldnt even have been an HRO. The HRO-50 was introduced in 1950 and was followed quickly by the HRO-50-1 that added an extra IF amplifier and, to improve selectivity, double IF transformers were used in last two IF stages (three dual transformers that included a dual IF output transformer to the detector tube.) With 12 tuned IF transformers, the receiver was very selective. The HRO-50-1 was produced in 1951 through 1952. Early versions of the HRO-50 had grey grip knobs with bright aluminum skirts. Even the PW-D used the gray HRT-style knob on the earliest versions. Later versions will have gray knobs and the PW-D will have the standard HRK-style black knob. All HRO-50-1 versions have all black knobs. If the receiver is a table cabinet it will be labeled as quotHRO-50Tquot or quotHRO-50T-1.quot Rack mounts substituted an quotRquot for the quotTquot and are so-marked. Photo below left shows the chassis of the HRO-50T. Note the standard IF transformers used in the two IF amplifier stages. Also note that the two IF amplifier tubes are 6K7 tubes with grid caps. In the photo below right is the HRO-50T-1 showing the three IF amplifiers with the dual IF transformers that includes the input transformer to the detector stage. Also note, the 6SG7 tubes (no grid cap) for the second and third IF amplifiers. This receiver is also equipped with the optional NBFM adapter. The HRO-60 - The final evolution of tube-type HRO receivers was introduced in 1953 - the HRO-60. With 18 tubes, double conversion and a current regulator on the oscillators, it was the final evolution of the tube-type HRO. Double conversion was utilized above 7MC when using coil sets B and A or any of the A prefix bandspread coils available. Bandspreaded 40M required the C coil set which wasnt double conversion. The HRO-60 accessories included coil sets J, H, G, E and F, providing general coverage from 50kc to 430kc and 480kc up to 2.0mc. Additionally, an AC coil set provided bandspreaded 15 meter coverage. AD covered 6 meters. There were two other quotA prefixquot coil sets, the AA and the AB, both of which bandspreaded in the 27mc up to 35mc ranges. The HRO-60 was available from 1953 up to about 1964. At the end of production, the selling price had escalated to an unimaginable 745.00 As with all of the HRO receivers, rack mount versions were available that featured a 30quot tall table rack that allowed mounting of a coil storage unit and a rack mounted speaker. These rack mounted speakers with coil storage were available as early as with the HRO Senior receivers and, with the introduction of the HRO-50, the type SC-2 coil storage and speaker combination became available. Special quotdust coversquot were installed on these later rack-mount receivers that fit over the side panels and are held in place with two knurled thumb-screws. The HRO-60R is only labeled as HRO quotSixty quot with no specification as to its rack mount construction (the same is true for the table cabinet.) When using one of the rack mounted speaker set-ups one will notice somewhat of a reduction in the bass response due to the lack of any true enclosure for the speaker. This is typical of most rack mounted speaker set-ups. The HRO-60 first conversion oscillator frequency was changed during production. Early versions of the receiver used 2010kc while later versions use 1990kc. At least two versions of the manual were published with early manuals referencing 2010kc as the first conversion frequency and later manuals showing 1990kc. In fact, I have an original HRO-60 manual that has a hand written note saying quot1995kc - per Nationalquot, so certainly there was much confusion over what frequency was used in any particular receiver. While aligning any HRO-60, its easy to input a specific amplitude signal at 2010kc and adjust the two first conversion transformers for maximum output. Then measure the output of the receiver exactly - use an audio output meter connected to the 500Z ohm output. Next, input the same exact amplitude signal at 1990kc and readjust the first conversion transformers for maximum. Measure the output of the receiver exactly. Whichever alignment frequency results in the highest output level is the correct frequency for that receiver. The correct frequency should be marked on the two first conversion transformers for future alignment reference. gtgtgt photo above . 1955 HRO-60R sn: 393 0255, rack mount HRO-60 receiver in MRR-2 table rack with SC-2 8quotspeaker amp coil storage unit gtgtgt With the direct readout dial on the HRO-60 it is possible to achieve very accurate tracking. Youll find that it is tedious work since each LO low-end adjustment will require coil set removal, then making a slight adjustment followed by reinserting the coil set to adjust the high-end trimmer and then checking the tracking. With patience its possible to have the HRO-60 (or HRO-50) dial achieve a very accurate readout considering that its resolution is somewhat limited. Performance - The HRO-60 is often times berated as less of a receiver than its predecessor, the HRO-50 but this is mainly from hams who are looking for maximum bandwidth for AM signals. The early HRO-50 used two rather conventional IF amplifiers that provide a typical quotbell curvequot passband which many AM ops find pleasing to listen to. However, the HRO-60 and the HRO-50-1 were trying to cope with the crowded band conditions of the fifties and sixties where successful communication was the goal. The additional IF transformers and IF amplifier stage provided a narrow passband with steep skirts resulting in very selective tuning. An excellent Crystal Filter circuit also helped with difficult QRM. Operating a rebuilt and correctly aligned HRO-50-1 or HRO-60 is a pleasure - QRM is rarely (if ever) a problem and the receiver is still a competitive performer at any frequency. However, that isnt to say that the early HRO-50 isnt a capable performer that is able to handle QRM with its Crystal Filter and provide excellent audio when conditions allow for it. photo left . The HRO-60R chassis. The smaller IF transformers are for the first conversion set-up. Note the two dual IF transformers - the HRO-50-1 used three dual IF transformers. The rear of the chassis has the Calibration Oscillator installed but a NBFM module is not installed. HRO Serial Numbering System The Charles Fisher Survey - At first glance, Nationals serial numbering system seems confusing. There was a rumor that the serial number system was designed to hide the actual production quantity of receivers being built but this seems unlikely. Several years ago, Charles Fisher performed a survey of about 70 early HRO receivers to determine the serial numbering method that National used. His article was published in the AWA OTB in 1989 (it is also currently on the web - link provided below.) The Fisher article contains a wealth of information for the HRO enthusiast. The Production Runs - Fishers survey determined that National used a combination letter prefix and number suffix for their serial numbers on the early HRO line, e. g. D-12 or G-115. Each production run of receivers were given a new letter prefix and the numbers are then sequentially assigned. The first HRO run begins with prefix quotDquot and was probably only about 100 units. Run quotEquot and most subsequent runs are made up of about 250 units. Sometimes runs overlapped each other. Letters quotOquot and quotIquot may not have been used due to their similarity to numerals. By about mid-1938, the letter prefix had gotten to the end of the alphabet and the serial numbers were changed to number prefix with a letter suffix but numbers up to 500 were used, e. g. 123-F or 434-H. By the beginning of WWII, this type of serializing had reached the quotLquot suffix and was halted. Fisher wrote that during WWII, the numbering again changed - this time back to the letter prefix but using number suffixes higher than 250 with the exception of prefixes A, B and C which, since they were not part of the original serial numbering sequence, used numbers beginning with 1. Also, during WWII the letters quotOquot, quotQquot and quotIquot were used in the serial number combinations. There are many exceptions to the WWII serial numbering, though. Total production quantity from 1935 up to about the beginning of 1941 was around 8000 to 9000 receivers. Around 5500 to 6000 receivers comprise the letter prefix serial numbers with the remaining 3000 or so using the letter suffix serial numbers. Western Historic Radio Museum Serial Number Log - WHRM started an HRO serial number log for ALL tube-type HRO receivers in 2007. Our serial number logs for other communications receivers have been very successful in determining production levels and other interesting manufacturing data. One of the first discoveries for the HRO receivers was the change of format for serial numbers on the HRO-5A1 receivers that continued on through the HRO-60 receivers. Additional serial number reporting has revealed the dual prefix letters used during WWII. Please keep reporting your HRO receiver serial numbers. As seen, important information can be found when enough numbers are gathered. Use the e-mail link below in quotDating Early HRO Receivers by Serial Numbers. quot More on WWII Serial Numbers - After receiving several reported HRO serial numbers from enthusiasts, it has become apparent that several systems of serial numbering were used during WWII. Much of what Charles Fisher found is true but there are many exceptions turning up as more serial numbers are reported. The HRO-5W receivers seem to re-use older serial number sequences, note that the reported HRO-W receivers are all serialized with the quotKquot prefix. The serial numbers used for the HRO-W quotKquot run were certainly duplicates of earlier issues from the 1935-36 run. The same is true with HRO-5 sn J-39. Apparently, National believed that the HRO-5W was a different receiver, or at least different enough that it couldnt possibly be confused with the earlier HRO Senior - after all, the 5Ws used octal tubes. Additionally, there have been several HRO-M receivers reported that were serialized with a two-letter prefix followed by up to three numerals. AP-461, PC-67 and PP-988, for example (there are more.) Its possible that this double prefix was to avoid confusion with early HRO receivers built with the same number but with a single prefix, however PP-988 is much higher of a number than the earlier single P prefixes used so there might be another meaning to the double prefix. The two-letter prefix AP-461 is an exception since the single A prefixes were issued during WWII and had no special limitations since there werent earlier quotAquot prefixes issued. One note is that nearly all two-letter prefix HROs are located outside the USA. Possibly, the two-letter prefix identifies production runs that were specifically for Lend-Lease sales. Additionally, it can be noted that a single quotPquot prefix serial number has yet to be reported for an HRO Senior and only one HRO Junior has been reported with a quotPquot prefix number. This leads one to speculate that perhaps the quotPquot run in 1936 was a relatively small quantity allowing WWII use of the quotPquot prefix with numbers as low as 150 or so. Certainly, WWII was a hectic time for National HRO production and variations in their serialization of receivers should be expected. Keeping the serial numbering format and sequences in order was probably very low on the quotlist of prioritiesquot at National during WWII. Even post-war serializing was not consistent and variations should be expected until around mid-1946. Post-WWII HRO Serial Numbering System - With the mid-1946 HRO-5A1, a completely different method of numbering was used consisting of two groups of numbers with no letters. The format is usually three numbers, a space followed by four numbers, e. g. 184 1054. This serial numbering format was used from the HRO-5A1 up through the HRO-60. It appears that the first three digits identify a production run and the four digits identify the particular receiver in that run. Note the reported HRO-5A1, HRO-50 and HRO-60 receivers and that the production run digits progress higher from the HRO-5A1 (184) to the HRO-60 receivers (345, 366, 393.) Also, note that all of the later receiver identification numbers consist of a zero followed by three digits (indicating that production run levels are seldom more than a few hundred receivers.) Dating HRO Receivers by Serial Numbers Charles Fishers Survey Charles Fisher compiled a list of serial numbers from 70 early HRO receivers during his survey for the AWAs OTB article. By using the serial numbers compared to the evolution of the example it was possible to extrapolate a logical sequence of serial numbers. To the right is Fishers table of serial number prefixes and suffixes, which identify the specific production runs, tied to probable dates of manufacture. Since the survey was only concerned with early HRO receivers the cut-off for entry into the survey was that the receiver had to use the plug-in crystal on top of the crystal filter unit. The dates only go up to the beginning of production of the HRO-M receiver which had crystal installed inside the crystal filter unit. Charles Fisher didnt publish the complete serial numbers of the 70 HRO receivers reported in his survey. He reports quantity per production run letters only. Here is a link to the complete Charles Fisher article: FISHER: Dating the National HRO WHRMs National HRO Serial Number Log I have started a serial number log here for ALL tube-type National HRO receivers. The log will be divided up for each model of HRO and will include all tube-type models from the first HRO receivers up to the HRO-60. This log will eventually be an on-line source for dating any of the HRO receivers. The more serial numbers sent in, the more accurate the data will be. If you have several HRO receivers, be sure to designate which serial number goes with which model receiver. Serial Number Locations On HRO receivers from 1935 to early WWII versions, the serial number is stamped next to the Antenna-Ground input terminals insulator block, between the insulator block and the left edge of the chassis. This allowed the serial number to be easily viewed by looking through the square hole for the antenna input located on the left side of the receiver. Late in WWII, the HRO-5 and HRO-W had the serial numbers stamped to the left side of the audio output tube between the tube socket, the meter zero pot and the left edge of the chassis. This required lifting the receivers lid to see the serial number. Early post-WWII receivers use the same location next to the audio output tube. With the introduction of the HRO-5A1 and the new serial numbering system, the location was moved to the right side top edge of the chassis mid-way back. This location was used up through the HRO-60 production. Pre-WWII HRO Production Runs versus Build Dates SN Letter Prefix Probable Dates D, E January-March 1935 1935 - Runs D, E, F, G, H amp J White quotpearlizedquot push-button S-meter switch (D, E) - S-meter switch changed to black push-pull switch (F-on) - The push button switch was noisy in operation and quotpoppedquot through the audio when released. Additionally, the push button required the operator to hold the button down with one hand and tune in the station with the other hand - inconvenient at best. White coil graphs (D, E,early F) - Coil graphs changed to black (mid F-on) - black graphs did not show moisture stains or possibly glue stains. Coil shield boxes on 1RF, 2RF and Mixer have only one access hole for alignment. LO shield box has two holes. This is for runs D, E and early F only. Mid-F-on two holes are found on all Coil shield boxes. Additionally, runs D, E and early F will have very small contact buttons on each of the coil insulators. These buttons are the connections from the coil set to the receiver. Mid-F-on these contact buttons become a two-piece assembly that is larger and taller. Also, runs D, E and early F have coil insulators with no embossed nomenclature. Coil insulators on runs mid-F-on have quotNational Co. quot and pin numbers embossed into insulator. Metal case non-illuminated S-meter with 0-5 scale (D-J) - 0-5 scale conformed to early QSA signal reporting method. 5 is at half-scale with nothing indicated on the arc of the scale above 5 (except as noted below.) - All E production run receivers seem to have the meter cases with a smooth quotroundedquot flange. The earlier D-runs and post-E runs have meters that have a slight indentation along the rim of the flange. The difference is subtle. Possibly a component cost resulted in the use of a different style meters during the early production runs. METER SCALES - D-run S-meters have a pinkish-gray colored NC diamond logo with white quotNCquot, quotPLUSquot is printed above 5. This same scale was also used on the E-run but late E-run meters may have the later 0-5 scale. Later, by F-run meters, the NC diamond is reddish-orange with black quotNCquot and the quotPLUSquot is no longer printed above 5. For examples of each meter scale see photos C and D in quotFeatures Found on Earliest HRO Receiversquot in a section above. For F-run to J-run type of scale see photo of HRO SN: F-09 in quotCollectors Galleryquot in a section below. Round IF cans (D-P) - hex adjustments of air trimmers required special tool (insulated .25quot hex screw head driver) - these are actually quotslottedquot screw heads that have been soldered over so only a hex adjustment tool can be used. An early Millen article on the HRO in quotShort Wave Craftquot issue of March 1935 shows the HRO chassis. Interestingly, chassis photo also shows the BFO can with an adjustment knob on the top. Fisher reports this BFO knob is also seen in a rear page photo in first instruction manual. Doubtful this knob was on any production units. Black chassis (D-L) - conformed with the SW-3 and FB-7 chassis paint use Tuning condenser insulators are stamped out of sheet insulating material leaving rough edges used on D and E runs only. With run F, the tuning condenser insulators are molded bakelite with smooth edges and have a embossed spacer where it meets the metal spacers (F-on) - the bakelite insulators were less hygroscopic than former material which tended to warp in excessively humid areas quotNCquot in red background on the dial pointer mounting screw (D, E-partial, F-partial) - Dial pointer mounting screw changed to plain nickel-plated quotraised diamondquot (G-on) - cost reduction. Fisher indicates that the quotraised diamondquot first appears on the E runs but is intermixed with earlier quotNCquot pointer until G run. The quotNCquot pointer emblem mounting screw was also used earlier on the SW-5 escutcheon. Many D and E run HRO receivers no longer have the original quotNCquot mounting screw because this part was very fragile and tended to break after a few times of removing the upper rail (which was necessary for coil set alignment.) The replacement was naturally the later version part, the quotraised diamondquot mounting screw-nut assembly. No pilot lamp (D, E) - Pilot lamp incorporated (F-on) - there was no visual quotpower onquot indicator until the pilot lamp was installed No external standby switch terminals (D-E) - Stand-by terminals marked quotBSWquot ( B SW itch) added to rear of chassis (F-on) - allowed for remote control of B, typically with a T-R switch that controlled the transmitter and receiver operation. Initially, the quotBSWquot terminals allowed a parallel connection with the B quotON-OFFquot panel switch. This required the receiver be operated with B quotOFFquot on the panel switch and then allowed the remote switch to control receiver operation. The parallel connection is shown in the 1936 manual. By 1937, the quotBSWquot terminals were then connected in series with the B quotON-OFFquot switch. This allowed the B panel switch to remain in the quotONquot position and still allow remote switching. Also, the panel B switch was functional as far as being able to remove (only) the B independent of the remote switch in the quotreceivequot position. This function would be necessary when changing coils. If the 1937 or later HRO receiver was going to be operated without a remote T-R switch, as in a quotreceive onlyquot installation, then a jumper had to be installed across the quotBSWquot terminals to allow B to be routed to the B quotON-OFFquot panel switch and allow receiver operation using the panel B switch. White ceramic resistors with hand written values in blue ink (D-F) - Black ink-stamped values (G - R) - both types of resistors were built at National. By run R resistors are purchased from Centralab. Tubular paper dielectric capacitors used in the first few production runs appear to be Micamold manufacture. This is a departure from the Sprague capacitors that National used in the AGS and FB-7 receivers. It has been reported that HRO J-123 (from early 1936) has all original Aerovox capacitors installed. Also, its been reported that HRO N-146 was equipped with paper capacitors that only had the values, a run number and a foil indicator band on each capacitor. By production run-V (as seen in V-35,) National had returned to using all Sprague manufacture capacitors (change probably happened much earlier.) A close examination of the under chassis photo used in the 1935 and 1936 manuals will show that the paper capacitors are Micamold manufacture. Note that the cathode bypass electrolytics are of Aerovox manufacture, however. Its likely that National was watching expenses due to the Depression and shopping around for the best prices from various capacitor companies. German Silver plated PW-D micrometer dial (D-H) - the Index and Number dials are cast pot metal made by Doehler Co. Very fine castings on early dials since they were to be German Silver plated. Later castings used for Lacquer painted dial (J-on) are poorer finish casting since the paint acted as a quotfillerquot and the final finish was smooth and even. Since white paint was used for the index lines, the engraved index lines are somewhat wider (to accommodate the paint fill) when compared to the plated dial (except for early painted dials which still have the narrow index lines - probably up to the end of 1936.) Antenna-Ground connector uses quotpushquot connectors with insulated button on top, fiber insulated mount (D - suffix B) - buttons are always missing indicating that these pieces tended to break easily. First production run units (D-run) will have the A-G terminal insulator strip mounted further into the chassis leaving about a 0.5quot space for the serial number. With run-E, the A-G terminal insulator is mounted much closer to the chassis edge leaving only about 0.25quot for the serial number. Also, D-run receivers will have the ground lug and wire mounted with a screw and nut centrally in the blank area adjacent to the 1RF coil terminal block. Run E units and later have the ground lug and wire attached to the mounting screw for the audio output tube shield because holes for optional audio output transformer mounting. From run-E on, five 0.25quot holes and four 0.125quot holes are stamped into the chassis in this formerly quotblankquot area to allow mounting an audio output transformer, if requested. This was commonly requested by military users and some commercial users. The five larger holes are for the transformer leads and the four smaller holes were to mount the transformer. S-meter potentiometer is located closer to the meter in the blank area of the chassis near the 1RF coil terminal insulator on first production run (D.) Pot moved to between the Ant.-Gnd. terminal insulator and the Audio Output tube shield for run-E on. Pot location moved to allow for mounting holes for optional audio output transformer. National Co. decal added underneath the cabinet lid by G production run. Cabinet has small 0.25quot holes in the rear panel for ventilation - enlarged holes and louvers on the sides appear with J production run Small skirted knobs have short round boss on lower part of square bakelite portion of knob grip (D - J) - The later knob grips have a round boss that is much taller (after J.) There are also changes to the skirt in thickness and depth of engraved nomenclature. Earlier skirts tend to be thinner with shallow engraving. Early Crystal Filter shafts support bearing is screw-mounted to inside of the front panel (D - F.) Later shaft supports are screw-mounted to Crystal Filter assembly (F-on.) TC wire connection from Crystal Filter housing to Tuning Condenser frame added for better ground connection of the tuning condenser shields ( G-on.) Appears sporadically on earlier production. Early ceramic (Isolantite) sockets, National type XC, used for front-end and 2nd detector tubes (five sockets total.) (D - V) XC sockets are replaced with later version National sockets (Steatite, ceramic similar to Isolantite,) type CIR, that have a metal mounting flange (by V, probably earlier.) 1936 - Runs K, L, M, N, P amp Q S-meter scale changed to 0-9 (J-on) - the scale change was to follow amateur adoption of the RST method of signal reporting - scale remains white with black numbers, red NC diamond with black quotNCquot S-meter case changed to a bakelite housing (J-on) - it was possible for B to appear on the metal zero adjusting screw, new design corrected this. At first this meter version was not illuminated. Illumination added to meters by mid-1937 which corresponds to the addition of this type of meter to the NC-101X receiver. German Silver plated PW-D micrometer dial changed to quotblackquot lacquer (J-on) - cost reduction because the paint can act as a filler. This allowed Doehler to use castings that were not as quotfinequot of a finish as was required for the German Silver plating. The new painted PW-D also conforms with introduction of NC-100 models (although the NC-100 dials are painted bluish-gray on the Index dial and red on the Number dial.) NC-100X receivers used the same bluish-gray Index dial but the Number dial was black instead of red. Airway Receivers used gray Index dials with black Number dials. NC-101X generally uses the same quotblackquot dial as the HRO (although early versions may have the same PW-D as the NC-100X.) Paint color varies on HRO receivers PW-D and generally is found in colors that vary from dark gun metal gray up to dark bronze. There is no chronology to the variability of the paint shadings so it possible to find PW-D dials of any combination fitted to almost any National receiver. Perhaps this was intermixed stock or due to specific parts shortages - or maybe the subtle paint shading wasnt important to National. Unfortunately, its very difficult to confirm authenticity of any PW-D fitted to any HRO since the PW-D could have been changed at anytime by contemporary collectors. One more note on PW-D paint. it seems likely that Doehler supplied National with just the PW-D castings and the actual painting of the PW-D was done at National. This would allow National to use whatever colors they needed without requiring Doehler to stock various paints and keep track of what orders required what paint. Much easier if National handled all of the painting of the PW-D parts. This would then account for the many variations found in the PW-D color tints. Holes top rear of cabinet enlarged (J-on) - better ventilation of cabinet. Louvers added to side of cabinet (J-on) - better ventilation of cabinet Chassis paint changed to gray (K-on) - probable cost reduction by conforming with NC-100 and newer models HRO Junior introduced (February) - standard HRO construction but without Crystal Filter, S-meter or S-meter Switch. Only one coil set is included with the receiver although there are four specific coil sets for the Junior. All Junior coil sets do not quotband spreadquot (general coverage only,) have only one frequency graph and are identified with a quotJquot prefix. Specific Junior coil sets are JD, JC, JB and JA. After the HRO Junior is introduced the standard HRO is referred to as quotHRO Senior. quot National may have based the Junior on some versions of the HRO that they supplied to American Airlines. One of these AA-HRO receivers has turned up with a serial number prefix of quotJquot (sn J-245) which would be pre-date the February 1936 introduction date of the quotcivilianquot HRO Junior. The story of James Millen coming up with the Junior because of ham requests for a less-expensive model HRO is from a QST open-letter by Millen explaining the origin of the Junior but Millen doesnt mention the American Airlines version in the letter. Dec.1936 issue of QST, back inside cover National advertises a Gray quotLeatherettequot Finish HRO in a table rack MRR and speaker-coil storage panel SPC. Ad runs several times in 1937 and 1938. National would do special orders requiring special paint colors. RCAF Blue is probably the most often seen version. Other color variations are certainly possible since National did their own painting. NOTE ON VINTAGE WRINKLE FINISH PAINT: Why is the wrinkle is only on the outside of the cabinet Originally, wrinkle finish paint was a two-part process that first used a nitrocellulose lacquer base coat that was in the color the cabinet was going to be - black, for instance. The base coat was allowed to dry for several minutes to several hours. The length of time the base coat dries will determine the intensity of the wrinkle (longer drying time results in finer wrinkles.) Then the cabinet was painted with a catalyst that was usually tinted the base color. The amount of catalyst sprayed also determines the intensity of the wrinkle. The cabinet was then put in an oven as the wrinkle effect had to be heat-induced. After removal from the oven and cooling down, the wrinkle was set. Sometimes an additional coat of base lacquer was applied over the wrinkle to protect the final finish. So, that is why today when looking at an original wrinkle finish paint job, the outside of the cabinet has the wrinkle effect and the inside of the cabinet is smooth finish. Unfortunately, this two-part wrinkle is no longer available and we are limited to the one-step finish from VHT for black. VHT is very close in color and fairly close in pattern. Like the original formula, VHT must be heated to wrinkle properly. 1937 - Runs R, S, T, U amp V S-meter changed to a bakelite housing, illuminated unit - made by Marion Electric Instrument Co. - scale is white-colored plastic - 0-9 S-units in black with black arc above S-9, red NC-diamond. IF cans changed to square units (P-on) - improvements to air tuning condenser design in square IF transformers, adjustable with insulated blade screw driver. The adjuster heads on these air condensers were round so a hex adjusting tool wouldnt have been useable, therefore National had to leave the slotted heads as the means of adjustment. quotBSWquot terminals are changed from parallel connection with panel B switch to a series connection ( R-on.) Requires a jumper across quotBSWquot terminals to operate receiver without a remote T-R switch. Tuning condenser spacers are changed from quotturnedquot hex stock to all round stock - cost cutting measure as the spacers didnt require machining now. White ceramic resistors changed to standard purchased parts with BED code (resistors purchased from Centralab at that time) Value of C7 erroneously shown in parts lists as far back as the first manual as .1uf 200wvdc was actually a .01uf 400wvdc capacitor. Close examination of the under chassis photos used in manuals in 1935 and 1936 show that C7 was a .01uf 400wvdc cap (the value can be read in the photo) and that the error was in the parts list. Later receivers will have a .01uf 600wvdc brown square bakelite (probably Aerovox) capacitor installed. WWII and post-WWII returned to tubular capacitors of .01uf 600wvdc. Additionally, C-28 is listed as a .01uf 600wvdc tubular capacitor but nearly all receivers will have a .01uf 400wvdc tubular capacitor installed. Ceramic tube sockets replaced with newer style quotCIRquot sockets made by National Co. - sockets have a metal mounting flange. ( V, possibly earlier) Hex head screws used to assembly Crystal Filter unit. ( V, possibly earlier) 1938 - Runs W, X, Y, Z amp Suffix A S-meter changed to a yellow scale unit with 0-9 S-units in black and 10db to 40db arc scale in red and quotDB OVER S-9quot in red. Marion Electric meter. Installed by run-W. This corresponds with the change in the S-meter used in the NC-101X around the same time - early 1938. ID tag added to upper right part of front panel - the uninformed would now know what kind of receiver they were looking at - mid-1938 Serial numbering system changed to numeral prefix with letter suffix - the quotZquot prefix was used 1939 - Runs Suffix B to Suffix F Antennaground terminal changed to polystyrene insulator and screw binding posts - the older quotpushquot connector plastic top cap broke easily - new style connector by SN: 233-C Model 697 power supply for 6.3vac tube HRO Sr. introduced 2.5vac tube HRO not offered - only 6.3vac tubes used after 439 - Millen recanted his opinion that the 6.3vac tubes caused modulated hum at 15MC in the receiver - improved tube quality sited James Millen Resigns from National Company 539 - James Millen left National in May 1939, officially to form his own company, James Millen Mfg. Co. but it is thought that Millen was adamantly against Nat ional going into the quothome radio marketquot that was being promoted by some of the company money holders. The talk was that National would supply quotWardsquot or quotSearsquot with home radios. Millen had worked for the past eleven years to put National as the leader in shortwave communication receivers and it seemed that some quothigher-upsquot in the company wanted to quotchange directionquot from this successful business position. Millen resigned but National never went into the home consumer market at that time. Demands from WWII in Europe resulted in huge orders for HRO receivers which rendered the argument for change moot. Some of Millens close friends relate a different story however. It seems that Millen had gone to Washington D. C. to discuss the use of the HRO receiver in the military. At the meeting, Millen represented himself as president of National. With Millens quothigh profilequot at National, to many customers this seemed like the actual status-quo. Somehow word got back to William Ready (the actual president of National Company) who was livid. During the meeting at National (upon Millens return) Millen was asked to resign, which he did. It seems like an over-reaction on Readys part, who was generally regarded as an easy-going, well-liked CEO. Apparently there was much more involved in Millens resignation and perhaps the Washington incident was just one of many factors in a Millen-decision that had been quotbrewingquot for some time. Needless to say, Millens departure, for whatever reason, was the beginning of Nationals slow downhill spiral as far as technically innovative designs. Of course, James Millen Manufacturing Company wasnt particularly innovative either and was still selling 1940s parts and gadgets in the 1960s. Millen actually made his company successful by being an electronics contractor and building oscilloscopes for RCA and two-way radios for GE. The ham gear and old style parts were Millens way of staying active in the ham radio business. 1940-1941 - Runs Suffix G to L Tuning condenser insulators redesigned, shield thickness increased, improved grounding contacts for rotor (Suffix G-on) - better performance with cost reduction HRO Production and Engineering Changes from 1942 to 1953 1942-1945 - General Information - Various Production Runs during WWII Bandspread coil production is significantly reduced (eliminated) as the military production requires quotJquot series coil sets for A, B, C and D frequencies. Most of WWII coil sets are JA, JB, JC and JD coil sets along with E, F, G, H and J coil sets. Coil set C, LO inductance adjustment is changed to a moveable quotloopquot as coil sets A and B. Many HRO receivers will have audio output transformers installed to remove B from the speaker terminals. Sometimes seen pre-WWII military units but becomes common during the war. RBJ, RAW and RAS introduced in 1941 for USN. These are rack mount HRO Junior receivers with speaker, power supply and coil storage box included in rack. RAS has 175kc IF for uninterrupted coverage from 190kc up to 30mc using seven coil sets. RBJ coils are apparently for 456kc IF but have some differences because the individual coil are identified with numerals that are different than either the HRO or the RAS. Power cable from the RAS was a shielded cable even though it was cloth covered. USCG designation of RC-105 used for HRO Senior version with GC coil sets. Coil sets have metal ID plate. Speaker was designated R-115 and was 8quot PM in the MCS cabinet with metal ID plate on upper right front of the cabinet. Plug-in coil sets - front panel changed from 316quot thick aluminum to 18quot thick steel Many of the slotted head machine screws used in assembly of various parts are replaced with hex head screws with .25quot hex heads. The gear box is changed from a casting to a sheet metal assembly with square edges and corners. quotNCquot is stamped-embossed on the sheet metal cap. This incorporates a mounting change from four fillister head screws for mounting the molded cap to only two hex head screws to mount the new style cap. Additionally, the sheet metal housing requires that a bronze bearing be installed at the rear to act as a thrust bearing for the worm gear. Also, since the sheet metal housing isnt as thick as the old cast gearbox, the condenser supports are now integral to the assembly which limits the clearance for the thrust ball bearing assembly. This forced the assembly of the ball bearing thrust assembly on the worm gear shaft to now have the ball bearing at the front of the shaft rather than next to the worm gear flange as originally designed. During WWII the wrinkle finish paint formula was changed and the quotwrinklequot tends to be much finer than early model HROs. During WWII there were many variations of the HRO, the coil sets, the power supplies, etc. built for the Signal Corps, the Navy and for Allied use - not all variations are covered in this article. Later HRO-M, MX receivers will have ID rings for AVC and B toggle switches. Many HRO-M, MX receivers fitted with Marion Electric 0-1mA scaled, non-illuminated, white scale S-meter. Toggle switch replaces the quotpull-switchquot for the S-meter function. HRO-5 introduced in 1945 with following changes: Change over to mostly JAN parts, specifically most resistors are changed to JAN type All coil sets now have an aluminum, silk-screened panel that is mounted on top of the coil set panel to provide coil identification and provide a frequency graph and a logging chart All coil forms used in all coil sets are now made out of polystyrene plastic Crystal filter changed to internal mounted crystal. This change may have been incorporated earlier in some receivers but it is consistently used in the HRO-5 and later receivers. Serial Number location changed to near AF Output tube and meter zero adjustment. This location is sometimes used in earlier quotLend-Lease receiversquot with two prefix serial numbers. Hum-resistor eliminated from tube heater circuit and one side of the heaters then connected to chassis instead All tubes changed to octal tubes, all metal octal tubes except 6V6GT AF Output tube S-meter is almost always a Marion Electric 0-1mA meter with white scale and non-illuminated Cabinet changed to have no ventilation holes in back and no louvers on the sides. Heavy duty 697W power supply is introduced with square box type cabinet rather than the typical National quotdog housequot cabinet. HRO-W produced for Signal Corps - mid-1945 Late-1945 - 1946 - General Information Bandspread coil sets return to production. Possibly as early as September, 1945 - when civilian sales start up. HRO-5 becomes HRO-5A when bandspread coils are supplied. S-meter scale returns to a white scale with diamond quotNCquot logo installed in WWII Marion bakelite case. Some meters may be older Marion Electric types with round housing and yellow S-meter scale. HRO-5A1 quotearly versionquot introduced around Feb or Mar 1946 - Features Noise Limiter built onto a small chassis. These receivers use many quotleft overquot parts from WWII production and will be found with round Marion Electric S-meters from pre-WWII production, HRO-W front panels, National ID tag will be mounted above the NL control on receivers with WWII panels. When these panels run out, then the tag is returned to the upper right corner of the panel. Meter Zero Pot location moved behind Audio Output tube socket HRO-5A1 quotlate versionquot introduced July 1946 - Features an quotimprovedquot Noise Limiter circuit that is now built directly onto the chassis. New quotstandardquot circuit for Crystal Filter that uses a six-position Selectivity control and a variable capacitor Phasing control - end of the dual variable capacitor type Crystal Filter. Wider spacing between Selectivity and Phasing controls on new filter. Also, for HRO-5A1 quotlate versionquot - New serial number location on right side-top of chassis edge midway back Also, for HRO-5A1 quotlate versionquot - New serial number format using three digits to identify the production run, a space and then four digits to identify the receiver Also, for HRO-5A1 quotlate versionquot - Same cabinet as late WWII used with no ventilation holes in back or louvers on sides but quotNCquot decal now applied under lid (was discontinued during WWII) Also, for HRO-5A1 quotlate versionquot - New S-meter with square shaped housing made by Marion Electric. Conformed with the S-meter used on the NC-240D Also, for HRO-5A1 quotlate versionquot - Cadmium-plated chassis replaces the gray-painted chassis Late 1946 - HRO-6 introduced with a supposedly quotimprovedquot Noise Limiter circuit - external appearance of receiver remains unchanged. Its known that HRO-6s and HRO-5TA1s were built with-in the same production run - run 184. See quotHRO Serial Number Logquot (above) - the two reported SN for HRO-6 are production run 184 0297 and 184 0697 and five of the HRO-5TA1 serial numbers is also production run 184 . Its also interesting that three HRO-5TA1 receivers apparently have higher serial numbers than the highest HRO-6. It appears that the HRO-6 serial numbers are inter-mixed with the HRO-5A-1 serial numbers. Its possible that National considered designating the quotlate versionquot of the HRO-5A1 as an HRO-6 since there were so many changes to that receiver from the proceeding versions. Perhaps some of the quotlate versionquot HRO-5A1 receivers were tagged as HRO-6 since there appears to be no physical difference between the examples other than the ID tag. National probably stopped using the HRO-6 designation because of the developing design work for the HRO-7. From the serial numbers it appears that only a small quantity of HRO-6s were so designated. probably less than 100 receivers. 1947-1953 - General Information HRO-7 introduced in mid-1947 - major redesign of external appearance, coil graphs, coil removal levers (new,) voltage regulator added HRO-50 introduced in 1950, followed by HRO-50-1 - major redesign of receiver with HRO-50 having built-in power supply, direct readout dial, push-pull audio - HRO-50-1 adds third IF amplifier and uses two dual-IF transformers With HRO-50 or 60, coil mounting insulator blocks are changed to ceramic material. Switches are added to eliminate the need to move the four screws when changing to general coverage or bandspread HRO-60 introduced in 1953, adds double conversion above 7mc. The 7mc coverage with double conversion requires that the user employ the B coil set in general coverage. If 40 meter bandspread coverage is desired then the C coil must be used and this coil operates in single conversion. Additional coil set offered - 15M (BS only,) 10M (BS only) and 6M coil sets available Most of the following items are actually necessities for operation of the receiver and some, like the four coil sets A, B, C amp D, were included with the purchase. However, power supplies, speakers, coil boxes and extra frequency coverage coil sets were optional and added to the total cost of a receiver. Ive also included Nationals Servicing and Upgrading as this was an option that many owners took advantage of. HRO Coil Sets - Detailed Information photo above . Top coil set is from HRO sn: F-13 and shows the white background graphs. Bottom coil set is from a later HRO Senior showing the black background graphs General Information - Each of the HRO coil sets consist of four shielded coil assemblies that function in the receiver as the 1RF, 2RF, Mixer and Local Oscillator tuned circuits in conjunction with the HRO receivers tuning condenser. The early coil sets were identified by the users by looking at the graphs and seeing what frequencies were covered, however, National identified each coil set with a letter. Coil sets A, B, C and D covered 30mc down to 1.7mc and could also be set to bandspread the 10M, 20M, 40M and 80M ham bands. Very early on, the E and F coil sets were added. These two coil sets allowed coverage of the AM BC band and provided the user with coil set E that would cover 160M and also allow leaving the D coil set covering 80M bandspread. Eventually, coil sets covering the long waves were provided with G, H and J coil sets allowing coverage from 430kc down to 50kc with a small section of the spectrum around the receivers IF not covered (430kc - the upper frequency of the G coil to 480kc the lower frequency on the F coil.) During WWII, almost all A, B, C and D coil sets produced were of the quotJquot series, or HRO Junior coil sets that didnt provide the bandspread function. Many WWII coils sets had small aluminum tags installed between the frequency graph and the logging chart for coil set identification. Very late in WWII, a silk-screened panel was introduced that showed the tuning range graph with logging chart and the coil set identification by letter. These remained on the post-WWII HRO-5A and HRO-5A1 receivers with a bandspread graph added in place of the logging chart on sets A, B, C and D. The HRO-7 changed the metal tag to a rather long frequency graph for general coverage and bandspread with coil set identification. The HRO-50 and 60 use only a letter identification on the coil set panel. The HRO-50 letter ID is engraved while the HRO-60 uses a medium-sized rectangular metal silk-screened tag. Early coil panels are made out of 316quot aluminum. During WWII, the panel material was changed to 116quot thick steel. Early Production - The coils sets that were provided with the HRO receivers in the first three production runs are somewhat different from later production. The photo above shows the early white background frequency charts used on early coil sets compared to the black background charts used on most of pre-WWII production. To the right shows the alignment access holes used in early coils (photo A) versus the access holes in later coil sets (photo B.) In the photos to the right, Photo A shows the contact insulators used on early coil sets from the first three production runs. Note the small contact buttons and the lack of any nomenclature except for the quotB3quot engraved coil identification. Photo B shows the type of contact insulator used on coil sets up to the change to ceramic insulators for the HRO-50 series. Note the larger, two piece contact buttons and the embossed nomenclature quotNATIONAL CO. quot along with the quotNCquot diamond logo and contact button number identification, which is difficult to see but consists of a number below the contact. Coil Assembly Construction and Alignment - The two holes on the top of the coil shield allow access to the trimmer capacitors for general coverage or bandspread alignment. Coil sets E, F, G, H and J provide a padder adjustment on the LO coil that is accessible from the top of the coil set since the bandspread function is not provided on these coil sets. The holes in the rear of the coil shield allow access to the padding capacitor that is used for bandspread only or the LO inductance adjustment for general coverage. The LO inductance adjustments on coil sets C and D consist of the brass metal disk inside the coil form that rides on a threaded rod. The metal disk is spring-loaded to retain its adjustment and can be changed by rotating the disk on the threaded rod using the hex nut provided to move the disk further into or out of the coil form. Since the disk is made out of brass, the further into the coil the disk is moved the lower the inductance is adjusted. Note in the photo to the right the various adjustments provided on the Local Oscillator coil. It can be seen in the photo that both coil assemblies use the brass disk for general coverage inductance adjustment. Differences are that the coil assembly to the left is from a very early coil set (D-run) and has a hex head adjustment on the bandspread padder condenser. The newer coil assembly on the right is from a 1936 coil set (J-run) and it can be seen that by this time the bandspread padder is slotted for screwdriver adjustment. The upper air variable capacitors are general coverage and bandspread trimmer capacitors. It can be seen that the type of air variable was changed to a more quotfixedquot assembly by replacing the hex nut and threaded end on the rotor with a press-fit rotor plates into the brass rotor shaft assembly. This applies to the bandspread padder also. Since coil sets B and A are operating at a much higher frequency, a different LO inductance adjustment is utilized. This inductance adjustment consists of a loop of wire at the end of the coil wrap that is located inside the coil form. By moving this loops position, the inductance of the coil is changed. The loop from an A coil can be seen in photo A to the right. During WWII, coil set C LO was changed to quotloopquot adjusted L. In photo B to the right, note the compensation condenser behind the bandspread padder condenser. Note also that this padder adjustment is a compression capacitor. This is a Mixer coil assembly showing the difference in construction. Nowadays when aligning the HRO coil sets, just adjusting the top trimmers will usually align the coil sets fairly well. See quot Restoring and Aligning HRO Coil Sets quot in the section below for more details on alignment. Also, all HRO manuals have the detailed procedure for full receiver alignment and owners should use that as a reference as well. Individual Coil Assembly Identification - Looking closer at each individual HRO coil assembly, it will be noted that a number and a letter are engraved into the insulator block of each of the coil assemblies that make up the coil set. The letter will designate the frequency range and the number identifies the function of the particular coil. Thus coil assembly quotC3quot is the Mixer coil for the 3.5-7mc tuning range or coil assembly quotA4quot is the LO coil for 14-30mc. During WWII, the RAS version of the HRO Junior was built for the USN. To have this receiver tune uninterrupted from 180kc up to 30mc, it was necessary to move the IF down to 175kc. This will require slightly different coil assemblies and these were given a different identification code. A coil set for the RAS that has a coil assembly marked quotG6quot will indicate that the assembly is RAS RF2 for 180kc to 430kc. The only RBJ coil Ive seen is a 50kc to 100kc LO coil that was identified as quotJ12.quot Also, on other J coils (50 to 100kc) the HRO-W RF1, RF2 and Mixer coils are marked J1A, J2A and J3A while the LO coil is marked as J4. The various codes are shown below. During WWII, the engraved coil ID was changed to an ink-stamped ID and remained ink-stamped through the HRO-60 production. Since its very easy to remove the coil assemblies for cleaning and restoration, it convenient that each one can be easily identified for proper reassembly. Band Spread - On pre-WWII coil sets, the tuning range graphs can instantly identify a coil set as belonging to the bandspread types A, B, C and D by the fact that two different graphs are provided. The left side graph is for general coverage and the right graph is for bandspread. Switching this function is accomplished by moving a 4-40FH screw from threaded holes in each of the insulator blocks - see photos above. The screw position should correspond with the position of the proper graph to select either general coverage or bandspread, e. g. screw in left hole general coverage, screw in right hole bandspread. NOTE . Only the A, B, C and D coils sets can be set to bandspread the amateur bands 10M, 20M, 40M and 80M. The bandspread option was eliminated from most of the WWII coil sets. When the bandspread option was eliminated from the A, B, C or D coils, a quotJquot was added as a prefix, thus a non-bandspread quotCquot coil would become a quotJCquot coil. The quotJquot prefix originally came from the pre-WWII HRO Junior coils that were non-bandspread coils but was later applied to many coil sets used during WWII. Some coil sets will have numerical identification with the various USN versions of the HRO Junior known as the RAS, RBJ or RAW having coil sets numbered 1 through 7. The HRO - 5 and the HRO-W (Signal Corps) were also provided with quotJquot prefix coil sets. Post-WWII coils return the bandspread function to the A, B, C and D coil sets. Coils with quotJquot Prefix quotJquot prefix on Frequency Range on A, B, C amp D coil sets Non-band spread version (HRO Jr. and most WWII coil sets) Coil Set Serial Number Location - Since the coil set of four A, B, C amp D were sold with the receiver, they are serialized with the same letter-number combination as the receiver. The original four coil sets were aligned to their specific receiver, thus the importance of having the quotmatchedquot original coil sets. If optional coil sets were ordered post-purchase of the receiver then coil sets were not serialized. If optional coil sets were ordered with the receiver then generally they were serialized since National aligned them before the complete order was shipped. Any of the coil sets, regardless of the serial number, can be used with any HRO but they must be aligned to the receiver that they are intended to be used with for best performance. The coil serial numbers are usually stamped on the LO coil shield. Sometimes the serial number will be stamped on the Mixer coil shield or the upper rail of the coil support on the right side of the coil set. Any sort of cleaning, past or present, tends to remove the ink-stamped serial number so its common to find coil sets that appear to be un-serialized. Depending on the cleaning, sometimes a quotshadowquot of the serial number can be discerned in certain light. By observing the various acceptance stamps and marks on the coil sets, its possible to see a similar markings within a receivers four coil sets that would tend to confirm that a complete set is matched to the receiver, even if the serial numbers have been removed by cleaning. Some of the acceptance markings were in wax crayon and other more resistant material and these usually survive moderate cleaning efforts. Medium Wave amp Low Frequency Coil Sets - Coil sets E, F, G, H and J cover the frequency range from 2000kc down to 50kc with a 50kc gap around the 456kc IF of the HRO. All of these coil sets had only one graph provided since band spread was not available. E and F provided a logging chart for favorite AM BC stations. MF and LF coil sets G, H, and J also provided logging charts for coastal station settings and other types of stations that were operating in that region of the spectrum. The plastic cover that was installed over the logging chart was a matte finish that allowed writing (in pencil) on its surface, thus stations could be logged without removing the frame and plastic cover to write on the paper logging chart. The quotpencil on plasticquot writing could be erased if station logging changed. Buying the E coil provided a ham with a way to have 160M coverage and then to have the D coil set to bandspread the 80M band. E and F coil sets were fairly popular sellers with the hams and its not too unusual to find an HRO that has six original coil sets A through F. photo right: G coil set showing the logging chart with matte finish plastic cover that could be written on with pencil The G, H and J coil sets were more for commercial use at shore stations, airports and with other users that needed coverage of the lower medium frequency range and low frequency range. During WWII, most HRO receivers were equipped with full sets of coils, so its not uncommon to find the military versions of the G, H and J coil sets. During the 1930s, 40s and 50s, most (if not all) ship to shore traffic, ship navigation, air navigation, weather forecasts for aviation and sea, time signals and the military (especially the Navy) were on the lower frequencies and the amount of interesting signals found there was incredible. Listening on the lower frequencies was extremely popular. Of course, the use of the quotlong wavesquot has changed over the decades since then and nowadays almost all of the signals in that region of the spectrum are now using digital or data transmissions. If you listen below 530kc without the receivers BFO turned on, youll hear very little. This has led many casual listeners to believe that nothing can be found below the AM BC band. Additionally, this part of the radio spectrum is subjected to a lot of man-made noise along with considerable noise from solar activity. Special antennas are required for successful reception of signals below 530kc. photo right . This is the quotH2quot coil (RF2) from an H coil that covers 100kc to 200kc showing the much larger inductances required to tune in the LF range. Since the H coil is a general coverage coil only one trimmer capacitor is required. This is a WWII vintage coil assembly showing the polystyrene coil forms. Post-WWII Coil Sets - During WWII, probably with the HRO-5W, all of the coil forms used in all of the coil sets were changed from the brown phenolic material to polystyrene. Polystyrene plastic was used up through the HRO-60 production. With the introduction of the HRO-7, levers were installed on the receiver to allow extracting the coil set and the coil set panels had guide pins that interfaced with the levers. This eliminated the grab handles on the coil set panels. This type of coil panel with guide pins was in use through the HRO-60 production. These later coils had ceramic insulator blocks that integrated switches that easily allowed selecting bandspread or general coverage. These switches eliminated the nuisance of moving the 4-40FH screws to go from general coverage to bandspread. gtgtgt photo right . Post-WWII coil sets showing the HRO-5A1 coil set style with silk-screened panel that incorporates the graphs and coil set ID. The HRO-5A1 coil sets were the last type to use the grab handles. gtgtgt With the HRO-60, double conversion was added to the receiver. The actuation of the switch to accomplish the conversion is provided by the particular coil set installed in the receiver. Since double conversion only affected coil sets A and B, along with the other quotAquot prefix coils sets, AA, AB, AC, AD and ADX, only these coils sets had a hole located in the LO coil shield between the two rear alignment access holes. This additional hole is a clearance hole for the double conversion switch. When coils sets are installed that dont have the clearance hole, the switch is kept from actuating, keeping the receiver in single conversion. When any A prefix, A or B coils were installed into the receiver, the double conversion switch was actuated by allowing a switch lever to protrude into the clearance hole. photo left . Close-up of the LO coil assembly from an HRO-60 C coil set. Note that the insulator base in now made out of ceramic. Note also that the coil form is polystyrene which had been in use since late WWII. photo right . HRO-60 C coil set showing the metal ID tag, the locating pins, ceramic insulator blocks and the switches that allow selecting either general coverage or bandspread. The earlier HRO-50 coil sets will have the identification information engraved into the front panel of the coil set rather than the aluminum ID plate. Note that only the last four digits of the entire receiver serial number is stamped on the coil sets. In this case, located on the mixer coil shield is quot0255quot which is from HRO-60R sn 393 0255. Restoring and Aligning HRO Coil Sets Nearly all of the HRO receivers that are found today are missing most (if not all) of their original coil sets. This means that most HRO enthusiasts are always on the lookout for quotorphanquot coil sets, that is, coil sets that, for some reason, have become separated from their original receiver. These coils sets generally require a little work to have them quotmatchquot the intended HRO receiver. Additionally, every coil set that is going to actually be used in a receiver should be disassembled and thoroughly inspected, cleaned and then reassembled. After this procedure, the coil set will have to be aligned to the HRO receiver that it is going to be used with. This procedure assures that peak performance will result with the new coil set operating in its new quotparentquot HRO receiver. Disassembly and Cleaning - All four of the coil assemblies are mounted inside aluminum coil shields that are mounted to the coil set front panel by four screws that quotclampquot the coil shield to the rear panel. By loosening these screws (just loosen them) the entire coil assembly is pulled off of the rear coil panel. Now, remove the three screws on top of the coil shield that mount the coil insulator and slide the coil assembly out of the coil shield. Youll usually find spider webs, dead insects, dust and dirt, all depending on how and where the coil set was stored. Inside the aluminum coil shield will also have a lot of residue that should be removed. Clean by quotdustingquot - that is - use a soft bristle paint brush to dust off the dirt and insect debris. Be careful of the fine wires that connect the coils to the contacts. Carefully inspect all of the solder joints for cracks or poor soldering. Check the condition of the coil and dust off any residue. Check the trimmer capacitors for bent plates. If everything looks good, spray a very small amount of De-Oxit on the rotor contact and the adjuster screw plate and rotate the trimmer capacitor several turns to clean the contacts. Always use a 14quot Nut Driver to do this operation as this will prevent damage to the slots on the trimmer adjustments. Be sure to return the trimmers approximately to their original position. Return the coil insulator assembly back into the coil shield and install the three mounting screws. Install the entire coil assembly back onto the coil panel. Repeat this procedure for each of the four coil assemblies. When reassembly is complete, the coil set is now ready for alignment in the intended quotparentquot HRO receiver. Slotted Adjustment Screw Heads - These quotdomed shapedquot adjustments for the trimmers on the coil sets were actually made at National. The original adjustment heads were hex shaped brass. National added the dome using solder and then slotted it so the trimmers could be adjusted by either a hex tool or with a blade screwdriver. Sometimes youll find the domed heads so quotgnarledquot that the screwdriver blade wont move the trimmer and just slips out of the slot. You can resolder a new domed head on the bad trimmer and then slot it with a hack saw blade. Remove any residue afterwards. Also, shape the slot carefully so maximum blade contact is assured. This way the new slot will work fine. Be sure to re-lube the associated trimmer since the heat may have vaporized the old lube. Many times, the quotorphanquot coil sets we find are not specifically the type for the intended quotparentquot receiver. Maybe the coil set might be a military version with a steel panel but we want a pre-war coil set with an aluminum panel. Luckily, the coil assemblies themselves are interchangeable and can be interchanged from steel panels to aluminum panels with ease. All of the WWII production of A, B, C and D coil sets are non-bandspreading J-type coils. So, while electronically these coils certainly can be used, they wouldnt be proper in a pre-war HRO Senior. If everything is correct and only a coil assembly swap and chart-graph transfer is required the entire procedure can be accomplished in a few minutes. Sometimes, the coil panels we have to use are painted incorrectly for the intended receiver. Sometimes, the charts-graphs coverings are in bad condition or missing. More than once, Ive found coil panels where the grab handles were sawn off so the coil set could be used in an HRO-7 or later receiver. All of these conditions will require repainting the coil panel. Strip the coil panel of coil assemblies and the charts-graphs. Use stripper to remove the old paint. Mask the rear of the coil panel. I use VHT Black Wrinkle Finish (BWF) paint which has a good pattern that is similar to the original. Apply a very heavy coat of BWF and apply heat, either using lamps or a hand-held heat gun. Let the finished paint set for several hours before moving the panel. Let the panel cure overnight before remounting the coil assemblies and charts. Where the handles have been sawn off youll have to find a set of WWII HRO screw-on handles. The original handles used on the aluminum panels were swedge-mounted, which is why they were sawn off. Youll have to remove the rear panel by drilling out the rivets. What you end up with looks like the photo to the upper left. Note there is a heavy paper gasket between the two panels. Mount the new handles using countersunk flat head screws. Then repaint the panel. Now, remount the rear panel using quotfake rivetsquot made out of 6-32 FH screws. The screw heads will have to be turned down to fit into the small countersunk holes in the panel. Be sure that the screw doesnt protrude beyond the nut on the backside. If it does, it will interfere with the coil assembly insulator when mounting the coil assemblies. Mount the coil assemblies and then mount the charts and frames. gtgtgt HRO Restoration - Hints and Suggestions Manuals - Fortunately, the HRO didnt change very much from 1935 up to 1945. The receiver was so well thought out and so well designed, few engineering changes were necessary. As a result of this, almost any manual will provide enough correct information for operation, repair and alignment of most HRO receivers. Be aware that a few changes in resistor values occurred when the 6.3vac tube HRO Seniors became standard ( 439.) The screen divider (R10 amp R15) was changed slightly to provide a lower screen voltage for the newer manufacture 6C66D6 tubes. In the 1940s, National issued manuals that were usable for all of the HROs, e. g. the HRO, Senior, Junior, M, MX, RR. Later, the HRO-5 was also included in the compilation. These manuals are available as copies from several sources. If you are working on an early 2.5vac HRO be sure to use the earlier compilation for the correct resistor values. As for original manuals, they are interesting to own but not absolutely necessary as an information source. Even the Riders Perpetual Troubleshooters Manual Vol. VIII has enough information on the early HRO for repair and alignment. Capacitors - All paper-wax capacitors need to be replaced in any vintage receiver if you intend to operate the set more than just casually. In the HRO, all the capacitors are easy to access and replace. In fact they are so easy to get to, I usually go a step further in the restoration process and restuff the original capacitor shells with modern film caps. This is just a cosmetic issue and doesnt make any difference to the final performance but it preserves the original under-chassis appearance. The two cathode bypass electrolytic caps are riveted to the chassis with one of the rivet heads under an IF transformer shield. They can be dismounted, rebuilt and re-riveted - if you are a purest. Also they can be left in place, disconnected and the new replacement electrolytic cap mounted nearby if under chassis appearance isnt an issue. Actually, these two electrolytics were well built and many of the originals are perfectly usable. They were low voltage (25vdc) and were well sealed - just test, reform and use. Ceramic Lead-end Resistors - National made their own resistors. They consist of a piece of ceramic round stock that has been drilled lengthwise to accept small diameter carbon rods. The rods protrude out the ends and when the lead-end was cast, contact was made with the carbon rods. Usually two rods are used on larger resistors and one rod on the small size. Over the years the contact to the carbon rod(s) may become compromised or maybe the rod(s) will crack - either will cause the resistor value to change significantly. Usually a restorer will find at least a few of these National resistors that need to be replaced. If under chassis appearance is not important than just replace the resistor with a modern equivalent. If you want to preserve the original appearance of the National resistors then a reproduction has to be made. These are actually easy to replicate using the lead-ends removed from the original resistor - they just twist off without too much effort. Select the proper value IRC resistor (International Resistance Co. - the type made in the forties are the correct diameter.) Drill 116quot holes at the center of the lead end-caps and insert the resistor leads through the holes, sliding the end-cap on to the resistor body. Solder the leads to secure. Paint the resistor body white and youre done. Install the repro resistor. For larger types, use the closest size resistor and if necessary slightly enlarge the end-cap opening with the correct size drill bit to get the proper fit. See the quot 1935 HRO H-103 Restoration quot section further below for photos and more details. gtgtgt Crystal Filter Problems - Most of the time, the Crystal Filter works quite well and we hardly ever think about a problem developing inside. The quotONquot switch is incorporated into the SELECTIVITY control and actuates the filter when advanced. You can usually feel a slight quotthumpquot as the switch changes position since it is cam-actuated. Sometimes the cam wears or other mechanical problems happen requiring some adjustment to the action of the cam and switch. Geoff Wooster (in the UK) ran into a problem involving the crystals themselves. This problem showed up on two different filters. Oxidation on the plates inside the crystal housing caused the crystal activity to be much lower than normal. The filters acted more like attenuators than anything else. Geoffs solution was to disassemble the crystal and thoroughly clean everything including polishing the metal plates inside. This cured his filter problems. It is possible in humid areas that oxidation can work its way inside the crystal. It can take years but these crystals are over 70 years old now. James Millen mentioned the HRO crystal filter in one of his QST letters in the 1930s. His recommendation was to clean the crystal with denatured alcohol. He also mentioned that the crystal should be slightly loose in the holder. This would be the older plug-in style crystal used in the pre-war HRO. New Power Cables - If your HRO doesnt have its original power cable, examine the one installed carefully. The amount of current required to operate the tube heaters will cause a significant voltage drop unless the proper gauge wire is used in the cable. The 2.5vac tube heaters draw a total of 9.55 AMPS, or about 23 watts Also, there is a center tap resistor to eliminate hum that is also across the tube heater line. The 2.5vac HRO cable should have 10 gauge wire in the cable for the tube heaters. All reproduction brown cloth covered cables are inadequate due to the small gauge wire used in the cables, (there are two types of repro cables, one has six wires and one has eight wires.) Even connecting two or three wires in parallel will not lower the resistance enough, resulting in too much IR drop for proper heater voltage (along with heating up the wires in the cable.) The only solution is to build the power cable using two 10 gauge wires for the heaters and two 18 gauge wires for the B and B-(chassis.) The 6.3vac HRO Seniors are a different matter as they only draw 3.1 amps at 6.3vac for the tube heaters. By connecting two or three of the wires in parallel in the reproduction cables, adequate current carrying ability will result and the IR drop will be minimal. gtgtgt gtgtgt The National power supplies do have an increased voltage for the heaters at the transformer. Usually about 25 increase to compensate for the IR drop across the power cable but this was designed to compensate for cables having large diameter heater wires. The best test is to check the voltages with the HRO operating on the intended power supply and measure the heater voltage across the hum elimination resistor. Heaters should be within 5 - 10 of the specified voltage. With low heater voltage (gt20 drop,) the HRO seems to work okay but youll notice a general lack of sensitivity requiring the RF Gain to be advanced more than usual. Also, check B at the tie point where the cable connects. With low B, the HRO also might seem to work okay on the lower bands but the S-meter will not work correctly and the RF Gain will have to be near maximum for CW reception. B should be 230vdc at about 70ma. In actual measurements the B will vary depending on if the HRO is receiving AM or CW signals, how loud the set is playing, etc. - it is normal for the B to vary from 220vdc up to about 245vdc depending on the load. National stated that the HRO would work on as little as 135vdc B, but they did add, quot at some sacrifice in performance. quot Usually, the B IR drop is never a problem because the current draw is so low. Building a New Power Cable - Even if the original cable is tattered and worn, it is best to keep it since it has the correct current carrying ability for that HRO - but if the restorer wants to replace a missing old cable on a 2.5vac HRO with a new cable of the same original length, it will have to be built. The original HRO power cables were about four to five feet in length. In order to have the new cable be flexible and to have very low resistance, using modern quotauto-stereo-boom-boxquot cable is an excellent choice. quotStinger Proquot 10 GA Power Cable is easily available and comes in various color jackets - also it is not expensive. The quotStinger Proquot cable is extremely low resistance and is made up of a huge quantity of small gauge copper wires resulting in a very flexible, very conductive cable. When the two 10 gauge wires and the two 18 gauge wires are cut to length they can be wrapped with olive drab or brown colored cloth tape to make a cable. If carefully done, the new cable will look okay but, more importantly, it will work great. You will have to tin the 10 gauge wire ends before soldering them into the four pin plug. In fact, you may have to do a little quotsizingquot of the tinned wire ends with a file to get them to fit into the plug pins, but they will fit. When completed, you will notice that the voltage at the hum eliminator resistor will be very close to 2.5vac and that the HRO will perform better than ever. There might be some fabric braid that could be utilized as the cable cover. Sometimes certain types of round braided shoe laces can be quotopened upquot and used as cloth braiding. Its also possible that a special build from one of the antique automobile electrical harness builders could supply an authentic HRO power cable with the correct gauge wires and the proper cloth covering. Probably expensive, though. 2.5vac Tubes versus 6.3vac Tubes - The Myth - James Millen wrote, in his monthly QST letter of March 1937, a recommendation that when the HRO was operated on an AC power supply, the 2.5vac tubes should always be used. Millen stated that the 6.3vac tubes produced a noticeable increase in the hum level and noise that would in some cases mask weak signals. In the April 1939 QST letter, Millen recanted what the earlier letter had recommended. Millen stated that the 6.3vac tube quality had improved significantly and there was no longer any advantage to using the 2.5vac tubes. The letter elaborated that a modulated hum around 15MC had been an earlier problem with the 6.3vac tubes. Additionally, the letter mentioned the new Model 697 power supply for the HRO which provided 230vdc B and 6.3vac. Also mentioned was the fact that earlier HRO battery operated receivers could not be operated on the new 697 due to the B being too high unless the receiver was modified. Some former National employees speculate that the actual reason for continued use of the 2.5vac tubes was due to National being quotover-stockedquot with power transformers that had the 2.5vac winding which were essentially useless unless used in the HRO power supply. Unfortunately, many hams and collectors only remember James Millens original, 1937 remarks. This had led to an quot Urban Ham Legend quot that the 2.5vac tubes are superior and re-tubing a later HRO Senior with early style tubes will give great performance results. This isnt true. The first problem encountered might be insufficient current carrying ability of the power cable for the 9.5 amps required to operate the 2.5vac tube heaters. It depends on the particular HRO, although most do use the same power cable regardless of the heater voltage. Also, the screen divider was changed for the 6v HRO Senior to provide a slightly lower screen voltage required for the newer manufacture 6C66D6 tubes. A somewhat higher screen voltage was used on the old 5758 tubes and early 6C66D6 tubes. The later HRO Senior, with the 6.3vac tube IDs on the chassis, will perform great quottubedquot as it came from National. The early HROs that were originally 2.5vac receivers should be operated quotas designedquot - with the 2.5vac tubes. Although, the early 2.5 vac HRO can be re-tubed to 6.3vac and it will operate okay, you usually cant re-tube a 6.3vac HRO to 2.5vac tubes and expect it to work well without some modifications. Speakers - The HRO normally does not have an audio output transformer installed in the receiver. This was common practice when the HRO was designed. Most manufacturers mounted the audio output transformer on the speaker. This practice does allow full B to be present the speaker pin jacks at the receiver - always a source of unnecessary worry for electrophobics. Even the Navy worried so much about the B on the speaker pin jacks, they wanted output transformers installed on the HROs that they ordered (all military National receivers, in fact.) If you dont have the quotNCquot speaker, or you have the box with a non-original speaker and need an audio output transformer, the HRO output Z is 7000 ohms on the primary (single ended) and the speaker Z is usually 8 ohms. Most universal audio output transformers will have a range on the primary, e. g. 4K to 10K ohms Z and a selectable secondary of 4 or 8 ohms Z. These usually work fine with the HRO. gtgtgt gtgtgt Check the DC resistance of the primary, it should be around 150 to 300 ohms but this depends on the power rating of the transformer. Higher power transformers will have larger gauge wire used and therefore a lower DC resistance. You should go by the impedance first and just reference the DC resistance. There are many quotuniversal typequot audio output transformers that will work fine with the HRO. The Triad S-53X is an excellent choice (but certainly not the only one,) providing 7K ohm primary with an 8 ohm secondary with the primary DC R at 300 ohms. (Actually, the S-53X is a universal audio output transformer with the option of selecting many different combinations of primary and secondary impedances but a 7000 ohm Z primary and 8 ohm Z secondary are options that are provided.) Modifications - Unfortunately, the HRO and HRO Senior receivers were built during the Depression. This means that many hams - out of economic necessity - had to keep their receivers as long as possible. The temptation to modify a great design was going to be there. Also, during WWII there was a complete absence of parts for those hams who could still operate - the only way to legally operate was as part of the Civil Defense emergency nets that were on usually once a week during WWII (transmitters had to be registered with the Navy to be legally used during that time.) This also led to some modifications out of necessity in keeping the receiver operational. After WWII, cheap HROs were around and subject to more abuse during the quotmodification maniaquot of the fifties. Very few pre-WWII HROs are found today that dont have some kind of mods installed. Whether the receiver can be returned to original will require a detailed examination. Unfortunately, many hams drilled holes and cut panels or chassis to install their so-called upgrades. Certainly, the rarity of the HRO will dictate whether the effort is justified to return the great old receiver back to its original design and appearance. Be aware that National performed their own upgrades on receivers that were returned to the factory for repairs or quotupdating. quot Usually the caliber of workmanship and the engineering thought process is far superior to that encountered from the average quothamster. quot gtgtgt gtgtgt Post-WWII production, that is the HRO-5TA1, HRO-7, HRO-50 or HRO-60, are less likely to be found extensively modified. The abundance of surplus gear to modify and the fact that the receivers were new or fairly new seemed to curb quotcutting and hackingquot activity. Sometimes product detectors will be found installed in the NBFM accessory socket of the HRO-5060 but these are normally homebuilt and based on an article that was published in CQ magazine in the mid-sixties (later in Electric Radio.) The problem with the HRO-5060 product detector plug-in mod is that the BFO is normally disabled when in NBFM and the stock National switch is a special build that doesnt provide a terminal to actuate the BFO when in NBFM. A separate BFO switch is necessary although some mods have the BFO wired to be quotonquot all the time - okay for CW and SSB (the main concern at the time) but a problem if AM reception is desired. These mods are easy to remove and return the circuit to an original configuration. Operation today using the HRO-5060 is normally for vintage AM nets and the need for a product detector is nil. However, if CW or SSB operation is desired using a stock HRO-5060, just reduce the RF Gain and increase the AF Gain for the proper ratio of signal to BFO injection at the second detector - thats the way it was done before product detectors came along. HRO Restorations in Detail The following articles detail the restoration of a few HRO receivers. Each project has various techniques involved in the rework of some type of damage that is found from time to time, not only in HRO receivers, but in others types of equipment as well. Hopefully each Restoration Article will have some helpful information for restoring HRO receivers. 1935 HRO Receiver SN H-103 - Restoration To the right is a photo of HRO sn H-103 taken when the receiver was first obtained. It is obvious that the cosmetics were in very good condition. The yellow quotR-014-8quot designation may have been an identification for commercial use but nothing was documented as to its meaning or of the receivers former use. Most of the problems with H-103 were under the chassis. Foremost was the 1.25quot hole that had been punched in the front left section of the chassis. This was going to be a challenge to repair. Also, the receiver had been totally re-capped using modern-style yellow plastic capacitors. Additionally, there were some non-original resistors, a few modifications with some extra non-original parts installed. The goal in the restoration was to bring H-103 back to full operation using the original design circuit and using parts that would have the appearance of the originals but were rebuilt new parts. The most time consuming part of this kind of restoration is restuffing the paper-wax capacitors. Since I didnt have the original caps, I ended up robbing a complete set of HRO quotSpraguequot paper-wax capacitors from an old HRO parts set. NOTE: Run-G HRO receivers probably used Micamold paper caps but these are difficult to find so I used Sprague which were used in all post-1936 HRO receivers. These caps were restuffed using modern quotyellow jacketquot caps installed into the original paper-wax shells. The shell ends were then sealed with colored wax. Proper orientation was maintained though this was for aesthetics only. While this is sometimes tedious work, the end results are a receiver that looks totally original and performs as new. Photo right: HRO SN H-103 before restoration Below is a quotbeforequot photo of the underside of the chassis showing all of the non-original type capacitors along with other non-original parts and circuit modifications. Below is an quotafterquot photo of the completed restoration of the underside of the chassis showing how restuffing caps preserves the original appearance. Collectors Photo Gallery of National HRO Receivers E-mail us a photo of your HRO receiver along with some comments about your opinion of your HROs performance. If you are restoring your HRO, feel free to relate any rework experiences you would like to share. Photos can be of any of the HRO family of receivers. E-mail your HRO photo to: Western Historic Radio Museum - HRO Photo HRO SN: E-76 - Paul, W9AC, has recently finished his restoration of this second production run HRO SN: E-76 and the results are spectacular. Performance was improved in the LO section by adding a Collins silver mica 10pf NPO capacitor as the tuning condenser coupling capacitor and by adding zener regulation to the LO itself. Also, from Loren Windom in a 1940s QST article, some minor modifications to the LO section. The end result is a reduction of thermal drift and stability of the tuned signal when the RF gain control is adjusted. Paul also owns first production run HRO SN: 49. HRO SN: F-09 - This early third production run HRO is in excellent condition and has its original coils (six of them) along with the coil box and the power supply. Note that the quotNCquot pointer retainer screw is still being used at run-F along with the white graphs but the pilot lamp is installed as is the pull switch for the S-meter. A very nice original HRO owned by K4OZY. HRO SN: G-235 - This early HRO is owned by Greg, K6SRO. It dates from July 1935 and includes the matching coil sets in the National wooden box. The meter is the 1-5 scale early version meter with the metal housing. The Noise Limiter looks like it could be a DIY addition based on the standard National modification or it might be a National supplied kit. Greg is in the process of restoring this great example of the early HRO. HRO Senior SN: 170-H - This HRO is from Great Britain and dates from about 1940. It is owned by John G3SLX. 170-H is in great original condition and features an unusually heavy texture wrinkle finish paint. HRO-MX SN: D-706 - This is the WWII version of the HRO dubbed the HRO-MX. This version still has the large six pin glass tubes but many improvements were already incorporated by the time D-706 was built (probably around late 1944 to early 1945.) Note that the serial number uses the quotDquot prefix which was also assigned to the first HRO production run in 1935, however the number at quot706quot is much higher than the numbers assigned in the initial quotDquot run. Also, note that this receiver has the Marion Electric 0-1mA S-meter that was installed on some of the WWII production HROs. This HRO-MX is owned by Marc, GI3YDH, of Northern Ireland. HRO Senior - Modified by Royal Canadian Corps of Signals - In the late thirties or early forties, the Royal Canadian Corps of Signals ordered approximately 200 HRO Senior receivers. These receivers were modified to what the RCCS needed for their use. The addition of a shield to cover the tuning condenser can just be seen in the photograph to the left. The antenna terminals were replaced with a more robust British version. All controls were labeled using engraved tags mounted with screws. Additionally, a serial number tag was added to the lower part of the front panel. A Hammond audio output transformer was added to the chassis. Three phone jack were added to the front panel. The 2000 Phones was from the plate circuit of the 1st Audio Amplifier, 500 Monitor was from the cathode of the Audio Output tube and 500 Line was from the Hammond transformer. On the rear chassis a phone jack was added that allowed disconnecting the Hammond transformer and connecting a National speaker box or any other speaker that had an internal output transformer. There are other minor modifications to the back of the S-meter and the toggle switch replacement for the pull switch for S-meter disable. This RCCS modified HRO Senior belongs to Fred Archibald VE1FA, who has seen six other examples of this version of the HRO. Several versions were seen at swap meets in Canada and a couple have shown up on eBay. Photo provided by Fred Archibald VE1FA. Tom Brent reports that in 1975 Fair Radio Sales offered (on the front page of their catalog) these receivers quotin the wooden crate as refurbished by the Canadian governmentquot for the price of 125 with five coil sets included but no power supply. This information explains why so many of these RCCS HRO Senior receivers are found supplied with later HRO-5 type coil sets. Amalgamated Wireless Australasia (AWA) - AMR-100 - AWA of Australia offered this HRO knock-off during WWII. It came with five coil sets which were general coverage only. This wonderful example is owned by Peter Brickey K6DGH, who did the restoration. The front panel has been re-silk screened and the receiver is shown with its correct matching loud speaker. This AMR-100 also has its complete five coil sets. This is the second AMR-100 that Peter has owned. The first was found decades ago in a surplus store in California. That particular receiver was sold long ago. This second one was found at a ham swap meet in California about 15 years ago. Peter finds that his restored AMR-100 seems to out perform its National HRO-5 contemporaries. photo by: Peter Brickey K6DGH HRO Performance Comparisons The Early Competition - To say that there was no receiver that came close to the National HRO performance in 1935 is not an exaggeration. The competition consisted of the Hammarlund Comet Pro - a receiver that was designed before the AGS and didnt have an RF amplifier or any sort of dial calibration. It was a popular receiver that performed quite well up to the point where images and lack of sensitivity became a problem (around 10 to 12MC.) The fabulous Hammarlund Super-Pro was in its design stages and was still at least a year from release. The Patterson PR-10 was available and with an R-meter along with a 10 tube circuit it was a good receiver but with no RF amplifier, no xtal filter or calibrated dial (other than the BC band) it was limited by images at higher frequencies and QRM everywhere else. At the time, there were various after-market preselectors that could be purchased and used with any of these receivers, providing the necessary RF amplifiers to increase selectivity, sensitivity and reduce images. Radio Manufacturing Engineers had the RME-9D which did have an RF amplifier, R-meter and xtal filter along with direct frequency readout plus bandspread. It was a compact, well built, good performing receiver but suffered with an extremely poor tuning dial design. In November 1935, RME introduced the RME-69 . an excellent receiver that corrected the dial problems of its predecessor. Breting had just come out with the Breting quot12quot and this receiver had a TRF stage in addition to a non-tuned pre-amplifier that was switched in above 7mc. The quot12quot also had a crystal filter, R-meter, Volume meter and an illuminated, direct readout dial. Except for the lack of bandspread, the quot12quot had a lot to offer for about 100. In 1935, Hallicrafters was still having their receivers built by contractors and had not offered anything significant at the time although the very successful SX-9 was just about to be released (in late 1935.) RCA was offering the ACR-136 with an RF amp but no xtal filter or bandspread. It appears to have been a typical quotall-wavequot receiver for the SWL. RCAs AR-60 used double preselection on its three highest frequency bands but each receiver was literally quothand-builtquot and so expensive no ham could afford it (495 - not to mention that only a few hundred were produced.) The AR-60 was certainly intended only for commercial-military applications. The other receivers from Sargent . Ross or other lesser known builders were generally lacking an RF amp, xtal filter or bandspread. The HRO Design - The HRO was the only 1935 receiver that came with two stages of tuned RF amplification provided on all frequencies. This virtually eliminated images and later became the standard method used in single conversion superheterodynes for image reduction. The use of a plug-in coil module that shielded each coil and itself was installed into a shielded compartment assured that stray losses were not encountered. Connecting the coil set to the tuning condenser via flex finger contacts and short, direct buss wire assured that tuning losses were at the lowest possible. Efficient design of each tube stage, especially the First RF Amplifier, reduced thermal noise and increased the signal to noise ratio. These design factors allow the user to experience the best in sensitivity with low internal noise. Copying very weak signals is standard with the HRO - the signals would not even be heard on other receivers of the time. The other stand-out feature was the incredible bandspread. Though only available on the ham bands 80, 40, 20 and 10 meters, it gave the user unbelievable tuning with the micrometer dial providing the equivalent of nine and a half feet of linear dial for each ham band. Tuning across the ham bands seems to go on and on - it was literally the best bandspread system available. Performance Today - What about the HRO performance today with modern QRN and QRM levels The HRO is a very sensitive receiver capable of receiving DX signals that would be lost in the noise on other receivers. Of the many types of vintage receivers Ive used over a long period of time, I have always found the HRO to be the most consistent great performer when it came to receiving weak DX signals. The HRO is the only vintage receiver that Ive used that would receive Russian hams on 20M CW using just a wire antenna. This was in the mid-1970s when most UAUKs were not running much power and were always just above the noise, even in a then-modern receiver. Additionally, when it comes to QRM, the early HRO crystal filter is quite amazing. It is one of the few crystal filters that will eliminate QRM, even on AM phone operation. By tuning the AM signal quoton the nosequot with the crystal filter on you will notice just how narrow the bandwidth has become and a slight detuning will decrease the signal significantly. The same is true for CW but these days there is little CW activity, let alone CW QRM. The only receivers that approach the HRO in performance actually came out after the HRO. Heres three of them. The Hammarlund Super-Pro was introduced in March 1936 as a high performance, professional receiver. It is a great receiver that was built to a high quality standard and performed quite well. The Super-Pro had variable coupled IFs, high fidelity audio, accurate direct frequency readout. It also used double preselection on all bands and used a separate power supply. The only complaints heard regarding the Super-Pro is limited frequency coverage (this is for the X and LX versions though, the SX covered 160M to 10M), high front-end tube noise masking weak signals (mostly due to improper antennas) and non-calibrated bandspread dial (it was a commercial receiver, too.) In actual use, the Super-Pro is an excellent receiver with great audio but if you are looking for weak DX signals, you will have to use a matched antenna. Hammarlund expected the user to operate the receiver into a matched antenna system and did not provide an antenna trimmer adjustment. On the audio side of things, the Super-Pro has 14 watts of high fidelity audio available and it can sound incredible when the speaker is matched to the audio output Z. The Super-Pro has the power to drive the speaker to a thunderous volume. Certainly a rebuilt Super-Pro will perform as well as a rebuilt HRO in almost every type of reception. Separate power supply and speaker are the required accessories. Photo shows the 1936 SP-10 version of the Hammarlund Super-Pro. Radio Manufacturing Engineers RME-69 was another great performer that was a contemporary of the HRO. When used with the matching DB-20 Preselector, the RME-69 has three tuned RF amplifiers and is capable of impressive results. The bandspread is not calibrated but it has an ultra-smooth vernier effect. The built-in power supply is handy as is bandswitching the six tuning ranges. The dial nomenclature is miniscule and difficult to read but the dial illumination is great. The audio is single-ended and sounds pretty good driving a matched speaker. While you could get very good results with the RME-69DB-20 combination, just the RME-69 alone is a rather anemic performer. The build-quality the RME-69 is certainly far below the HRO with extensive use of compression trimmers for adjustments, even using compression trimmers for the LO adjustments. Additionally, the RME doesnt align the RF and Mixer stages but provides a quotTrimmerquot control on the front panel for peaking the stages for the frequency tuned. Finally, the RME-69 doesnt provide a remote stand-by function. Up to 1937, the RME was priced well below the HRO but when the price increased for the RME-69DB-20 in 1937, the cost difference compared to the HRO was minimal. The RME-69DB-20 only required a speaker for an accessory, maybe its only advantage after 1937. Photo shows the 1937 version of the RME-69DB-20 with matching RME speaker. 1940 Hallicrafters SX-28 - With five years of receiver development behind it, a rebuilt SX-28 will perform as well as a rebuilt HRO and it also has more features with less accessories. Unfortunately, double preselection is not provided on the SX-28 until band 3, or above about 3.0mc. Hallicrafters insisted that the only reason for two RF amplifiers was image rejection but certainly economics had a lot to do with their opinion. Sensitivity is very good with low thermal noise. While the calibrated bandspread is convenient to use on the SX-28, the quotextremequot bandspread that the HRO is capable of seems to be a better system when searching for weak signals. The P-P audio on the SX-28 has about 8 watts of power that when driving a matched speaker sounds very impressive with lots of bass and the speaker is the only accessory required. Like the Super-Pro, the SX-28 audio can reach thunderous volume levels. No doubt, the SX-28 will give an HRO serious competition, but after all, it came out five years later. Photo shows the 1940 version of the SX-28. Suggestions for Best Performance The Type of Antenna is Important - If the HRO is used with an untuned, random length, end-fed wire, performance results may not be up to the receivers capabilities (this is true for almost all communications receivers.) End-fed wires without a matching device are notoriously bad antennas - they are actually equally bad on almost all frequencies, so the user thinks the antenna is performing okay since there are no obvious peaks or nulls. However, with an antenna that is tuned for the received frequency, the HRO (and almost all receivers) will perform to its design limits. The HRO doesnt have an antenna trim, so when aligning the coil sets, the 1RF amp coil should be aligned to the station antenna, tuned for the specific band, for best performance. If you are an SWL, then the general coverage set-up should be used and the receivers 1RF peaked for maximum noise using the regular listening antenna for that coil range. More Alignment Notes and Coping with Drift - Proper alignment also is important for best performance with any receiver. Though it is possible to find an HRO receiver that is mostly original parts and is functional, it certainly will not be working at its design limits. A full rebuild is usually required for top performance. This is also true for orphan coil sets which might seem to function okay in a rebuilt HRO but full performance capabilities require that the coil set be fully cleaned internally, trimmers should lubricated and the coil set fully aligned to the HRO receiver that it is going to be used in. The original coil set alignment instructions had the user remove the upper front lid support thats held in place with two screws at each end and by the dial pointer mounting screw in the center. This was to allow easy access to the coil trimmers. Ive found that if you use a very long and thin blade screw driver with the metal shaft wrapped with tape (to prevent shorting to the condenser frame or the cabinet) all of the coil trimmers are accessible without removal of the upper lid support. The basic alignment is described in quot Restoring and Aligning HRO Coils Sets quot elsewhere in this article. The specific manual for the particular type of HRO will generally provide more details and should also be used when aligning the receiver. As far as the alignment of the IF and Crystal Filter, this is standard faire and as long as the IF is aligned to the exact crystal frequency, no problems will be encountered. gtgtgt gtgtgt The IF is 456kc and the crystal will be very close to this frequency. However, sweeping the signal generator across the IF can determine the exact crystal frequency and this is the frequency that the IF should be aligned to. In fact, your Crystal Filter will function better if you perform the IF alignment with the Crystal Filter on and set for fairly narrow selectivity. This assures that the Crystal Filter is operational and can be a useful tool for combating QRM. Although the manual will recommend that the BFO be set to zero-beat with the control at quot9quot this is not really necessary and actually reduces the effectiveness of the BFO. In the 30s and 40s the BFO was for CW and upper and lower sidebands dont even exist in that mode. Today we have SSB and by setting the BFO to zero-beat at 6.5 on the scale will allow you to select either upper or lower sideband when receiving SSB. As with all early receivers, the RF Gain must be reduced and the AF Gain set to near maximum with the AVC off and the BFO on to receive SSB signals. You have to set the receiver RF Gain so that the signal to BFO injection ratio is correct for non-distorted SSB reception. Coping with Drift - Drift is just a quotfact of lifequot for early receivers. There is a lot of discussion today for ways to eliminate drift in old receivers but it really depends on your individual method (or preference) of operation. Almost all amateurs in the 1930s and 1940s were on CW and they were always tuning the receiver during a QSO. That was just the way it was - you followed the received signals by frequent adjustment of the tuning dial. It became quotsecond naturequot for hams to quottune aroundquot for the best reception during a QSO. By the 1950s and later, voice comms were becoming more popular and a different belief was beginning to be instilled into hams - quotyou shouldnt have to touch the tuning dial on the receiver. The received signals (the transmitter) shouldnt drift and neither should your receiverquot As SSB came on the scene, the receiver required virtually no drift from either the LO or the BFO. This has resulted in todays hams expecting quotdrift-freequot operation in a receiver that was designed when CW was the primary mode of amateur comms and changing the frequency of the audio tone heard in a drifting signal didnt affect copy at all. Although quotdrift-freequot design was possible, the components and circuits available made this difficult to accomplish. Add in the economic factors of the Depression and it became next to impossible to build a quotsellablequot receiver that didnt have some drift. The HRO will drift in frequency for about 30 minutes and then settle down somewhat. In the bandspread mode the drift is much more noticeable. This is because of the resolution of the PW-D in the bandspread mode. A small drift of a couple of kilocycles appears as a drift of five to ten quotindex marksquot on the micrometer dial (depending on the coil set used.) So, if you want to operate your HRO quotas originalquot youll have to get used to the drift. Otherwise, you can change the LO coupling capacitor to a NPO type and add in zener regulation on the oscillators or build a regulated power supply for the receiver. Original is easier and better. Conclusions - The pre-WWII versions of the HRO receiver generally arent found in too many vintage AM ham stations today and thats a mystery. Why is such a high-performance communications receiver virtually ignored by the vintage AM enthusiasts Probably, its because the HRO is rather small and basic in its appearance. It doesnt have a large illuminated dial but rather has a device that requires the tuned frequency to be indirectly determined by referencing to graphs. It has single-ended audio, no tone control and the only selectivity control is via the Crystal Filter. It requires storage for the extra coils and it does require more accessories than normal, like the power supply, extra coil sets and speaker. However, when it comes to sensitivity you cant beat the HRO. When it comes to bandspread resolution, there is no better receiver than the HRO. The HROs later kin - the HRO-50 and HRO-60 are fairly popular today with vintage AM enthusiasts, still giving competitive performance even on 10 meters. These later receivers do feature a built-in power supply, push-pull audio and a direct readout dial which seems to confirm our opinion as to why theres a lack of interest in using the pre-WWII HRO as the station receiver. Today, the HRO is revered as one of the great designs of pre-WWII communications receiver production. Though collector emphasis and resulting high prices are on the rarer early versions, any of the HRO receivers will give the user superior performance, especially following a careful and thorough rebuild and alignment. With a production history spanning 30 years, certainly the HRO design concept was a long-lived one. It was a great receiver then and is still a fabulous performer some seventy-plus years later. photo above . 1935 HRO sn: D-65 (first production run) rack mount receiver 1. quot The Wonderful HRO Receiver quot by William Orr W6SAI, published in CQ magazine, May 1975 - Orrs article describes the origins of the HRO receiver 2. quot The HRO Report: Dating the Early HRO quot by Charles Fisher, published in AWA, Oldtimers Bulletin, Vol. 4 - 1989 - Fisher deciphers Nationals serial number system for the HRO, production history and engineering changes from 1935 up to 1941. Fishers article contains detailed information on early HRO production history and his observations from the results of a survey that references over 70 examples of pre-WWII HRO receivers. Fishers article is available on the web at: FISHER: Dating the National HRO 3. quot The Evolution of the National HRO and its Contribution to Winning WWII quot by Barry Williams KD5VC - Excellent detailed history of the entire HRO line, info on British use in WWII. Barrys article is available on the web at: Evolution of the HRO - Barry Williams 4. QST Magazines 1934 through 1939, various letters by James Millen, ads, etc. - Info on product development and upgrades, ads show evolution of the design 5. National Co. Inc. - HRO Manuals - detailed circuit description, design intent and performance expectations 6. Riders Perpetual Troubleshooters Manual - Vol VIII - most of the information needed for the early HRO receiver is in VOL. VIII 7. Article in Shortwave Craft March 1935 by James Millen - Basically, this is a detailed advertisement for the HRO, circuit description and schematic 8. National Co. Inc. Bulletin 250 1936 Catalog - Information on model numbers, availability and prices 9. National Co. Inc. quotThe HROquot Advertising Brochure - Information on circuit design and performance 10. quot Discovering Vintage Radio quot - Chapter 14, quotNationals Legendary HROquot - This is a British book with some interesting history and information on the HRO 11. quot Communications Receivers - The Vacuum Tube Era quot by Raymond Moore - Excellent reference book on HROs and all other models of tube-type communications receivers 12. Thanks to all of the National Co. Inc. and HRO enthusiasts that have sent in photos, serial numbers and other information. Your input has helped to expand this article and add detailed information on the production and history of these great receivers. Henry Rogers April 2007, new info added Jan 2008, Mar 2008, Sept 2008, June 2010 Entirely Re-edited, re-styled and expanded with new material to match our other communications receiver articles, corrections made, new photos - Henry Rogers 169 September 2011 More information and photos added: November 2011, January 2012, new photographs February 2012 March 2012 - Corrections to HRO-5A1, HRO-6 and HRO-7 introduction dates June 2012 - Minor corrections, Royal Canadian Corps of Signals HRO Senior - Fair Radio Sales info added, July 2012 - Additions to details on HRO-5A1 quotlate versionsquot and relationship to HRO-6 Jan 2013 - HRO Junior information expanded with new photos May 2013 - Correction to AWA reference - now Amalgamated Wireless Australasia August 2013 - More details on two-letter prefix SNs from WWII production January 2014 - More details on alignments of Coil Sets and IF alignment. Correction to assembly of the worm gear thrust assembly. May 2014 - Add info and photos of HRO N-130 Donations to Radio Boulevard - Western Historic Radio Museums Website If you enjoy using Radio Boulevard - Western Historic Radio Museums website as an information resource and have found our photos, our hard to find information or our restoration articles helpful, then please consider a donation to the WHRM website. A small donation will help with the expenses of website operation, which includes research, photographing and composition. WHRM was a real museum that was quotOpen-to-the-Publicquot from 1994 to 2012 - eighteen years of operation. WHRM will continue to provide its on-line information source with this website, which has been in operation since 1997. Please use PayPal for sending a donation by clicking on the quotDonatequot Button below Website Navigation Index