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...
Robot Eyes (CB12397E)
Found in a 1990 Electronics Handbook, this circuit causes an LED to flash when the phototransistor receives...
Zero crossing switch (CB21543E)
Found in a 1964 publication, this circuit makes use of transistors from the time. It operates on...