This high sensitivity sensor was found in a 1967 General Electric SCR manual. The circuit admits equivalents by triggering a load according to the used SCR.
The circuit shown is from the 1994 Linear Applications Handbook by National Semiconductor. Some of...
This circuit with two transistors was found in Radio Electronics magazine from February 1968. The...
This interesting circuit from 1967 documentation uses three series lamps to regulate the voltage...