This circuit was found in documentation from the 1980s. It is powered by the audio signal that must be cut. Transformers are the critical components and transistors are 2N2222.
This is a traditional comparator configuration to obtain an under and over voltage indicator. In...
This circuit with TTL output was found in a 1968 EEE. The transistor can be of general use. The...
This circuit makes use of a specific 80's component and was found in an American manual of the...