The circuit transistors, found in a 1974 documentation, may be the BC548. The circuit is used in quadriphonic systems to combine signals.
Using a piezoelectric sensor of the time, this circuit was found in the February 1994 issue of...
I found this circuit in an old English magazine from 1981, but it can still be assembled with some...
Only signals about 1 kHz can pass through this tuned circuit. The main component is a operational...