This little one-tube short wave receiver appeared in Popular Science 75 years ago this month, April 1940.  It uses as 12B8GT tube, a combined triode-pentode. The pentode section is used as a regenerative detector, and the triode is pressed into service as a diode, serving as the rectifier. The set runs directly from 120 volts AC. A 360 ohm resistor in series with the filament drops the voltage to 12 volts, and a hefty choke and two capacitors filter the power supply. Even though it’s run directly from the AC mains, the schematic shows no connections directly to the chassis, so as AC-DC sets go, this one is relatively safe to operate.

According to the accompanying article, the set could pull in signals from South America and Europe most evenings.

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