This amplifier was found in a 1970s documentation. Darlington transistors can be replaced for modern equivalents of at least 80 V x 2 A, equipped with good heat sinks.
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...