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.
We found this circuit in the August 1970 issue of Radio Elecronics magazine. It uses the CA3018...
This circuit was found in a 1997 documentation. The signals are adjusted in a double 555 (556) and the...
This circuit was suggested by Sprague Electric in an 80's documentation. The circuit uses a...