A young man drafted into the military during World War II could give himself an edge by having a useful skill, and the June 1944 issue of Popular Mechanics reported that pre-induction code practice sessions were well attended. This created a problem, since most code practice oscillators used headphones, and acquiring enough headphones presented a logistical challenge for those running the sessions.

The solution was offered in the form of a three-tube wireless code oscillator which would transmit modulated CW to a nearby broadcast receiver, producing room-filling volume. In light of wartime parts shortages, the circuit called for common receiver tubes which could probably be scavenged from another set. The plans called for a 6C5 rectifier, witn 6J5’s serving as AF and RF oscillators. The 6 volt filament voltage was obtained by wiring a 40 watt lightbulb in series with the filaments. The completed circuit is shown here mounted on a circular cutting board. The output of the oscillator was run to the receiver’s antenna jack, or simply placed near the set’s antenna.

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