Eighty years ago, these gentlemen probably realized that they would soon be serving in the armed forces, and their stint would probably be more comfortable if they came to their induction in possession of a skill useful to Uncle Sam. Therefore, they have undertaken to learn Morse Code, thanks to this one-tube oscillator described in the January 1942 issue of Popular Mechanics.

The set used a single 117L7-GT tube, whose 117 volt filament meant that it could run straight off the AC power lines, without worrying about dropping resistors or transformers. It had plenty of volume, which could be controlled with a volume control, to drive a speaker or up to 20 pairs of headphones for group practice.