This simple circuit is a continuity test that, in addition to testing resistors, can also test other components. Power is provided by batteries and the LED can be of any color.
This amplifier was found in a Japanese publication in 1972. Transistors are uncommon today, and...
The current of this source is 200 mA at the most, and the output depends on the zener that may...
Found in Mallory documentation from 1968 this circuit uses an integrated circuit from that time. The...