Microammeter (T465E)

Found in a 1948 MIT documentation, this circuit uses a 0 to 100 uA microammeter as an indicator. The power supply is 150 V.

Power grid voltage failure indicator (CB7013E)
Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the...
Electric fence (CB23675E)
This circuit with SCR and Unijunction and which can be assembled today with modern equivalents was found in a...
Intermittent Defects Detector (CB17230E)
This circuit was developed to find intermittent defects in an electrical control. In the event of a...