This simple radio was found in a Popular Electronics from the 90s. L1 and L2 have 100 turns on a toroidal core and L1 have a socket on the thirtieth turn.
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...