Seventy-five years ago, many would-be hams were applying themselves to learning the code, and the July 1950 issue of Radio-Electronics obliged them by providing the plans for this simple code practice oscillator. The circuit is simplicity itself, and is built in to a jam tin, complete with speaker. The 6-volt tube ran fine on 4.5 volts from three flashlight cells, and the circuit required no additional B+ voltage.

It featured adjustable pitch, and put out a clear tone through either loudspeaker or headphones.