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.
This circuit can generate signals from 100 kHz to 50 MHz depending on the crystal and the...
The circuit in the figure represents a typical application of a phototransistor exciting a relay...
Found in Philips documentation from 1968 this circuit operates at frequencies up to 10 MHz with 76...