This circuit is intended to recover a very weak signal at a receiver, for example, a CW signal or a tone signal. The circuit is from a Popular Electronics from the 90s.
This simple megaphone is from old documentation, but uses still current components. The circuit is...
Found in a 90s R-E Experimenter Handbook, this circuit has a greater gain than the previous one for...
This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and...