We found this circuit in a 1965 Electronic Design. Transistors are still common but admit equivalents for some of them. The circuit drains a current of only 4 mA.
Texas Instruments ESD122 Electrostatic Discharge Diodes (ESD) can be ordered from Mouser...
This circuit has a type of bias called "virtual earth" providing good gain, given by R2. The...
In this circuit the LED lights up when the voltage drops below the value set in the trimpot. The...