This circuit was found in a 73 amateur radio magazine from the 90s. An LED extends the scale from 0 to 5 V to 10 to 15 V in this bargraph circuit. Other zener values can be used.
This power supply uses a single-winding transformer. We found it in July 1984 Radio Electronics magazine....
This is an old circuit with a unijunction transistor from that time. We found it in a Radio...
Can be used as a shield, this old American documentation circuit offers digitally selected...