The circuit transistors, found in a 1974 documentation, may be the BC548. The circuit is used in quadriphonic systems to combine signals.
This circuit is from 1987 documentation. The original project was carried out with the tape...
This traditional crystal radio circuit, but which has a modern version with diode, was found in an...
This VCA was found in the July 1988 issue of Radio Electronics magazine. It uses an OTA op amp and...