This configuration similar to many of this site was found in 1965 General Electric documentation. Modern equivalent transistors can be used. LEDs can be used.
This circuit is from an Electronics Now from the 90s. It applies to almost any operational...
The basis of this circuit is the HA2400 released at the time. The circuit is from a Radio...
This capacitor leak detector was found at Popular Electronics in June 1991. The magazine no longer...