This circuit visually indicates that a high voltage is present in an outlet or other point. The neon lamp is common, and the appearance of the assembly is suggested in the same figure.
This circuit can work with almost any JFET. The circuit is from an Electronics Now from April...
This physical line servo control uses components that are not currently common. The circuit is from...
This circuit was found in a British documentation from 1969. It can be implemented with modern...