Can be used as a shield, this old American documentation circuit offers digitally selected attenuation values from 1 to 0.0001. The component used is uncommon today.
The oscillator shown in the figure keeps its frequency constant in an active cycle adjustment...
For bench use, this circuit functions as a bistable safety switch. The circuit is from a Radio...
In fact, this is the circuit also known as “vox”, that is, a relay triggered by sound. This...