This circuit serves as an audio output for AM or even FM radios and was found in a Radio Electronics magazine from March 1990. Note the supply voltages.
We found this circuit in an American 80's documentation. The resistors must be of high precision...
This circuit was suggested by General Electric in documentation from the 80s. SCRs are common...
This is a possible setting for a Colpitts oscillator operating in the audio track. The shunt coil...