AC voltage probe (CB8185E)

This circuit for voltages up to about 20 V was found in a 90s Popular Electronics. The LED can be of any type or color.

Anti-theft alarm with microswitch (CB26166E)
This circuit was found in the Electronics Experimenter Handbook of 1961. The circuit uses door...
Precision Diode LM101 (CB4607E)
The basis of this circuit is a National Semiconductor operational amplifier that functions as a...
Two-Transistor Darlington Amplifier (MSB035)
This two-transistor amplifier can be used as power stage for intercom, experimental receivers,...