Crystal oscillator up to 10 kHz (CB9500E)

This circuit was obtained from a Popular Electronics. The component is a UJT. The circuit has an oscillation point adjustment.

RF proximity sensor (CB8765E)
This capacitive sensor that operates with a high frequency oscillator was found in Radio...
Small Amplifier (CB969E)
This amplifier for the experimenter´s bench source 1 W and uses germanium transistors but can be...
Sound operated switch (CB9214E)
This circuit was found in a Hands On Electronics from the 90s. The microphone is a small 75-ohm...