Published in an old Popular Electronics, this circuit makes use of components that are still current. The circuit must be powered with 9 V and eventually adapted to function as a shield.
With two cascading tunnel diodes, this circuit found in a 196 General Electric documentation...
Found in General Electric's 1969 documentation, this circuit uses two Foto Darlingtons to control...
This circuit is used in the analog part of the telephone lines. The same circuit can directly...