Found in the February 1990 Radio Electronics issue, this sophisticated 100 MHz probe uses a period display module. The circuit has an external power supply.
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...
We found this circuit in a Radio Electronics from January 1967. The SCR is already the C106, which...
This power source with silicon diodes at a time when valves were still used was found in Radio...