This circuit that uses potentiometer tuning, was found in a documentation from the 80's. The integrated circuit used is from that time and is a not common today.
I found this circuit in a Popular Electronics from November 1999. The magazine is no longer...
This tunnel diode circuit was found in American documentation from 1966. The tunnel diode is the...
This circuit provides two slightly different audio signal outputs from a monophonic audio signal, so...