Silent alarm (CB22471E)

This circuit is from a Popular Electronics from 1992. The circuit powers an LED when triggered.

Constant Volume Amplifier 741 (CB13686E)
We found this circuit in a 1976 documentation. The FET can be BF245 or MPF102 and the power supply...
1A Flasher (CB9790E)
This circuit was obtained in a transistors manufacturer's manual from the 90s. The circuit uses an...
Field Strength Meter (CB1414E )
The instrument of this field strength meter, from a 1970s publication, can be a 200 uA...