Seventy-five years ago this month, the February 1943 issue of Popular Science carried the plans for this one-tube combination receiver and code practice oscillator. The construction article, by Arthur C. Miller, noted that thousands of young men and women were learning code for civil defense purposes or prior to enlistment in the Signal Corps. A code oscillator was then impossible to buy.

A single switch changed the set from receiver to code oscillator. As a radio, the set ran on 45 volts, but the code oscillator required only 4.5 volts.