The indicator for this circuit is a 0 to 1 mA milliammeter. The operational is from the 70s, when the circuit was published. Modern equivalent can be used.
This circuit was found in a 1962 publication. At the time there were high voltage batteries like the...
Found in documentation from the 1980s, this highly sensitive circuit is based on the conduction by the...
In the figure we have the way to implement a power zener diode. The voltage depends on the zener,...