Found in American documentation from the 1990s, this circuit has active cycle control. The basic components are given along with the diagram. Transistors are general purpose.
This circuit is from a technical documentation from Texas Instruments from 1978. In it we have the...
We found this circuit in a publication with experiments with operational amplifiers from 1973. The...
Using a varactor or varicap, this 1969 Electronics World circuit has a modulation range from 75...