This old voice circuit suitable for telephones of the time was found in a Radio Electronics from September 1973. The circuit is powered by a voltage of 7 V.
The purpose of this circuit is to keep the other phones on the same line muted when one is used....
Measuring capacitances and resistance this simple instrument was found in Radio Electronics...
The circuit shown is from the 1977 GE semiconductor manual. More modern equivalent SCRs can be...