This voice scrambler and descrambler circuit was found in a Radio Electronics from July 1963. Transformers are common types at the time with impedances according to telephones and line.
The operational amplifier can be of any type in this circuit, found in a 1974 publication. The...
Found in a 1967 General Electric SCR manual, this circuit triggers in case of excess current,...
With this configuration it is possible to obtain an 80 dB gain from two 741 operational...