Phone circuit (CB8709E)

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

35W Amplifier (CB10329E)
I found this circuit in a magazine Mundo Eletrônico, from the 70s published by my friend A....
Line amplifier (CB23746E)
This circuit was found in a Radio Electronics from June 1966. The transistor is from the time. The...
Photodiode Amplifier LM139 (CB15527E)
This circuit is a sensor for photodiodes that can be used in optical couplers, encoders and other...