This circuit is for old telephones with analog lines. It was found in the May 1988 Radio Electronics magazine. The circuit is powered by the line signal voltaje.
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...