Simple SCR alarm (CB22090E)

This circuit drives a buzzer or electric buzzer but can be used to trigger a relay or other load. The SCR can be any of the 106 family.

50 mW Amplifier (CB24449E)
This low-power transistorized amplifier was found in documentation from the 90s. The circuit uses...
Metal Detector (CB12077E)
This circuit is from Popular Electronics from March 1991. It can still be assembled with the...
Symmetric Power Supply (CB15712E)
The voltage of this symmetrical power supply depends on the regulating integrated circuits, which...