One-Tube Wartime Receiver, 1945

RadioCraftFeb45

Radio parts were in short supply during the War, and radio enthusiasts had to make do with what they had. “H.T.,” a resident of Bothell, Washington, apparently had in his junk box a 1D8GT tube, and a low-impedance earphone, and wanted to know what he could do with them. So he wrote to the editors of Radio Craft magazine asking for a diagram of a receiver covering the broadcast band making use of the parts he had. He wanted to mount the earphone in the cabinet for use as a small speaker.

The editors indulged him and provided this diagram in the February 1945 issue. It was reprinted from the July 1940 issue, and showed how the combination diode-triode-pentode tube could be used in this circuit. The triode section of the tube was an RF amplifier, followed by the diode detector, with the pentode serving as an audio amplifier. Unfortunately for H.T., the low impedance earphone would need to be used in conjunction with an audio transformer. This set would drive a pair of high-impedance headphones, but to use it with his low-impedance earphone, it would need to be wired as shown for the speaker. So H.T. had to find himself either a set of hi-z headphones, or the output transformer, in addition to what he already owned.

The other hard-to-obtain part would be the variable capacitor. The circuit here shows a ganged condenser, but the response pointed out that two separate condensers would provide better results.

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