This circuit is from a 1965 General Electric manual. It uses components from the time that admit equivalents. The SCR can be the TIC106 and the LDR of any type.
This PWM control circuit was found in an old documentation, but appears elsewhere on this site...
a We find this circuit which has a traditional configuration in a 1988 publication. The circuit is...
Indicated for applications with a PC, this circuit was obtained in an English publication in 1992....