This circuit was fond in an old publication of the years 1950. The transistors are germanium types and equalization is RIAA.
This circuit produces an intermittent ring tone being triggered directly by the telephone line. However,...
This circuit turns on the relay 12 seconds after S1 is closed. The time is given by C1. The...
This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is...