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.

Universal Battery Test (CB21347E)
This circuit was obtained from an English circuit manual. Components are common and LEDs can be 3...
Linear VCO (CB9429E)
Found in a 90's EDN, this circuit generates signals in the frequency range given by the graph. The...
100 kHz to 1 MHz Oscillator (CB12815E)
This circuit can generate signals from 100 kHz to 1 MHz depending on the L1 coil. For the medium...