This circuit is intended for underwater communications. Of course, the critical point is the shielding to avoid water. The circuit is from an Electronic Hobbysts Handbook from the 90s.
This circuit was found in a 2001 documentation. It is a test of zener diodes that uses a voltmeter or...
This simple transistor radio with only two germanium transistors was found in a Japanese magazine from...
The presented circuit produces the sound of a fireman's siren. In place of the output transformer with...