Transistor Radio 8TP-The design steps

Around the late 1954 Raytheon was fairly ahead in the development of a fully transistorized radio. As reported in Electronics, October 1954, a seven-transistor prototype had been donated to the Massachusetts Governor.
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In November 1954 the same magazine gave notice of a four-transistor radio by Regency being in production and available on the market. Texas Instruments supplied the transistor kit for it. See ‘Regency TR-1 - Early announcement’.

Early in 1955 the industrialization of the new radio in Raytheon was proceeding as planned, but they had to maintain their image as leading transistor supplier against TI. They had preferred a no compromise design of the new radio, setting the standard architecture for any future set, with a 455KHz IF, good sensitivity and enough output power with low battery drain. Time had been spent in the design of a lot of new components, suitable for operating with relatively high currents and low voltages, in particular in the design of coils and transformers. Probably to strenghten their image, early in 1955 they launched a relevant informative campaign. In the February 1955 issue of Electronics the production model was announced to be on sale for March 1 at 79.95 USD.

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In the March 1955 issue of the same magazine, Raytheon decided to disclose the design of their lab prototypes. The complete schematic diagram and circuit details were given in a three-page article. Here are some pictures of the prototype.

 
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Here is the diagram published in the same article.

The circuit is identical to the one given for production models. The only difference is in the audio output transistors, since in the prototype either CK721 or CK722 could be used, retaining the identical quarter watt max output power. In the text the authors W.E. Sheehan and J.H. Ivers give a lot of circuit details, explaining the reasons of the design choices. All the sections are explained, from the audio amplifier to the IF chain, to the class B transistor detector, whose 10db gain helps to properly drive the AVC circuit, to the oscillator-mixer circuit and components. Authors expect the use of a simple diode detector, provided that the IF gain could be slightly raised in the future. In the actual circuit two 30pF capacitors are used to prevent oscillations in the IF stages.

Also detailed data of the antenna and of the oscillator windings are given in the article, integrated by additional notes in the text. The next table gives a summary of the receiver characteristics.

                           

The new advertising campaign, from Electronics, May 1955, proudly pinpoints the combined offer of transistors and transistorized radios.

        

 

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