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 circuit was obtained in a 1973s documentation. The transistors may be BC558 for the PNP and...
Found in a 90's EDN this circuit can be used as a shield. The transistor is a general-purpose type and the...
This circuit was found in a 1980s Intersil documentation. The integrated circuit used is not...