Found in an old Popular Electronics this circuit is still current. The SCR can be of the 106 series and the relay according to the voltage used in the supply. The voltage can be 12 V.
We found this circuit in an old American documentation. SCRs can be modern equivalent types. The...
When the voltage exceeds the value given by the zener, this circuit from a 1990 documentation...
This circuit was found in a 1970s documentation. The components are from that time, and...