The main feature of this circuit found in an old American publication is that it is powered by the very signal it converts. The transistors are of the time and can be replaced by current types.
This 200-mW amplifier uses one of the first commercial power transistors. The circuit is from a...
Decade counters, such as the 4017, can be cascaded as sourcing signals with the frequency divided...
We found this circuit in an American 1980s documentation. The circuit uses a piezoelectric transducer...