Intercom (CB21660E)

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

Peak detector (CB9689E)
This detector with ultra-low deviation was found in an American documentation from the 90s....
Reversible sequential for LED (CB6945E)
This circuit is from an old Popular Electronics, but it can be easily implemented nowadays, even...
Classic Colpitts Oscillator (CB25646E)
This is the configuration of this type of oscillator given in an article in Electronics Now...