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.

1 kHz Active Band Pass Filter RC4558 (CB19782E)
This circuit uses two Raytheon RC4558 operational amplifiers that are similar to the 741. The...
Complementary Amplifiers up to 40 W (CB12354E)
This audio amplifier circuit is from Ibrape's technical documentation from the 70's. The BC177 can be...
Progressive relay switch (CB23775E)
This progressive circuit has a lock allowing coded activation. We found this configuration in...