This circuit was found in an Electronic Experimenter Handbook from the 90's. The coil can be formed by 4 turns of wire 28 with 0.5 cm diameter without core for the FM band.
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...