This circuit provides a reference voltage of 2.5 V adjusted in the trimpot. The transistor can be the BC558 (in the drawing it came out as NPN). The control is done by a rectangular input signal.
We found this circuit in an old American documentation for hams. The circuit serves as a telegraph...
The purpose of the diode in this oscillator circuit is to limit the amplitude of the output...
This circuit, from a component manual, also applies to other components in the same family. The...