Motorcycle headlight monitor (CB9117E)

This simple circuit was found in Popular Electronics from the 1980s. The circuit uses an LED as an indicator.

Clapp Oscillator (CB25316E)
This transistorized oscillator, a modification of the Colpitts oscillator, was found in the...
Photometer Using the CA3140 (CB433)
This circuit uses a CA3140, an operational amplifier with FETs in the input stages. Equivalent can be...
Signal Injector and Tracer (CB3917E)
This signal injector and tracer (follower) was found in an old American documentation. The...