Found in Popular Electronics from the 90s, this circuit generates signals in a frequency range set to R7 and basically determined by C1. Operational and equivalent transistors can be used.
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...