This circuit can be used with 5 to 15 V sources and the zener diode must be chosen according to the trip voltage of the protector. The circuit blows the fuse when the voltage exceeds the zener value.
This circuit is from 1968 documentation. We can assemble it with more modern components such as a...
Found in a 90s Silicon Chip documentation this circuit is intended to protect a speaker system in...
The UVTRON tube is an ultraviolet radiation sensor. In this circuit from Radio Electronics from...