Found in Philips' 1967 documentation, this circuit makes use of period components. The SCR can be of any type, depending on the power of the controlled load.
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...