3 A switched regulator (CB8859E)

Found in a 90s Popular Electronics, this circuit provides a current of 3 to 5 A depending on the transistor.

Bistable Multivibrator (CB9925E)
This circuit using an operational amplifier was found in old American documentation. It can be...
Simple transistor tester (CB23746E)
If the circuit oscillates, emitting sound, it is because the transistor is good. This simple...
Telephone Amplifier with TDA7052 (CB990E)
Like the previous circuit, this is used in the analog part of the telephone lines. The same...