Phone circuit (CB8709E)

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

CMOS Logic Test (CB14954E)
We found this circuit in an old documentation from 1979. It is a logic level tester that is...
Audio Booster (CB951E)
This booster circuit for audio signals, which is nothing more than an audio preamplifier for...
Ramp generator with integrator (CB21845E)
This circuit uses a feedback integrator. We found it in Ferranti's transistor manual from 1974....