This circuit is the receiver for the previous transmitter modulated by an audio signal. The transducer is a ceramic capsule, in which case the circuit becomes ideal for telegraphic transmissions.
This well-known siren configuration using complementary transistors is from a 1980s documentation. The...
This circuit was found in an old American magazine and could make use of more modern components...
This circuit is from the Philips integrated circuits manual of 1990. It is intended for magnetic...