Phone circuit (CB8709E)

With this circuit, found in a 80s Popular Electronics, it is possible to use two ordinary phones in a basic intercom.

5A Regulator 5 A LM2931-5.0 (CB14516E)
This circuit uses an unusual Motorola integrated. The circuit is from Motorola's 1990 Linear...
Buzzer Drive (CB25061E)
This circuit was found in a September 1987 Radio Electronics. The current through the switch is...
Cascading Voltage Triplicator (CB15448E)
The circuit shown in the figure triples the alternating voltage providing a continuous output...