This 1967 Ferranti circuit uses company components. These transistors can be replaced by modern equivalents. The sensor is an LDR.
This circuit is from 1968 General Electric documentation. It can certainly be adapted for any...
This tester from a 1960 magazine is only for capacitors with insulation voltages above 200 V (110...
Found in a 1991 publication this circuit can be assembled with more modern components. We can use...