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.

Timed Touch Switch (CB21298E)
This timing circuit was found in old documentation. The technology is CMOS. The supply can be made...
Oscillator with tunnel diode (CB8052E)
This circuit was found in a 1967 General Electric documentation. Tunnel diodes can oscillate at very...
Signal Weighting Circuit (CB25965E)
This circuit can be used in a signal level indicator with LEDs. The circuit is from an Electronics Now...