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.
We found this circuit in a 1968 Electronics World. The potentiometer should be set to trigger the SCR...
We found this circuit in a documentation from the 90s. It lets frequencies around 1 kHz pass,...
This wired intercom circuit was found in a March 1965 Radio Electronics. The circuit uses two...