This circuit was found in a 1980s documentation. The diodes may be general purpose diodes such as 1N34 or 1N60 and the indicator may be the lowest current range of a multimeter.
This circuit was found in the March 1992 issue of Radio Electronics magazine. The circuit has...
This circuit was found in Motorola documentation from 1969. The transistors are from that time. The...
This circuit was found in a 1991 publication. The transistor can be a general-purpose type....