This circuit was found in documentation from the 80s. It is based on unijunction transistors not very common today being synchronized by the 60 Hz power grid.
This precision speed control was obtained in an Electronic Design from the 90's. The output final...
Using the name of varactor this circuit was found in the Radio Electronics magazine of July 1982....
This trigger circuit was found in an American documentation from the 1980s. The amplifiers used...