Phone circuit (CB8709E)

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

Operational Astable (CB14826E)
This is the conventional configuration of an astable multivibrator with operational, found in a...
Triple 5 V Numitron power supply (CB8673E)
This 1969 Electronics World power supply has 5 V to power digital circuits and a 170 V output for...
Telephone Equipment Regulator (CB6030E)
The Texas TL783 integrated circuit is a three-terminal high voltage regulator with a wide range of...