This circuit was found in a 1968 General Electric manual. The circuit is for 3 A motors but can be changed according to the SCR used. The SCR is type 106 and R1 is 10k.
This circuit is from an English magazine of 1977. The circuit is still current, just using BC547...
The adjustment of the maximum load voltage is made in the trimpot. The circuit is from 1994...
In the figure we have the conventional configuration of a differential amplifier with the...