Using a 555, this configuration appears elsewhere on this site. This is from American documentation from the 90s. The indicator can be an LED or some device controlled by a relay.
This resistive load circuit for source testing was found in a 1991 publication. Power transistors must be...
No information is given about the transformers in this circuit suggested by Motorola in a 1968...
This circuit was obtained from the February 1990 issue of Radio Electronics magazine. The circuit...