Variable regulator with crowbar protection (CB21189E)

This circuit was found in a Popular Electronics from the 90's. The power transistors must be equipped with a heat sink.

Cascading the 4017 (CB25913E)
With this circuit any number of 4017 integrated circuits can be connected in series. The circuit is...
Injector and Continuity Tester (CB4452E)
This useful instrument has dual function, operating both as signal injector and continuity tester. The...
555 with duty cycle (CB24905E)
This circuit allows you to vary the duty cycle without changing the frequency. An interesting...