Intercom (CB21660E)

This good gain circuit was found in a Popular Electronics from April 1967. The transistors are germanium of the time.

S-meter (CB1405E )
The S-meter is signal strength meter, coupled to telecommunications receivers to indicate the...
Operational Connected Optocoupler Shield (CB16018E)
This circuit is suggested by Motorola, making it possible to use an optical coupler of type 4N26...
Dynamic Analyzer (CB12833E)
Dynamic analyzer is another name given to a signal follower or signal chaser. This circuit is from...