Fifty years ago, the October-November 1970 issue of Science and Electronics showed how to put together, at a total parts cost of about $4, this combination continuity-tester/code practice oscillator.

The circuit was dubbed by the author the “CON-TEST,” since it was first and foremost a continuity tester. But as the photo above shows, it was very suitable for use as a code practice oscillator.

The choice of transistor was not critical, but the author used a 2N170 for the audio oscillator, along with a 2N174 audio amplifier to produce some room-filling volume.