We found this circuit on a Radio Electronics. Similar configurations can be found in this section. The operational amplifier can be of almost any type.
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...