This circuit, found in a 1977 documentation, indicates when the grid voltage goes through zero. Under these conditions, it produces an output pulse whose duration depends on the capacitor.
Found in Popular Electronics from the 90's, this circuit makes use of components from the time. |...
This circuit for the logic control of the 555 in a power supply was found in the October 1989...
In this circuit, a light-sensitive SCR or Light Activated SCR determines the operation of an...