HI,

I intend to restore the above unit, but before I do so I want ensure that it is done with safety.

What size fuse would you recommend installing for a safe & properly working unit?

Thanks.

If a fuse isn't already fitted it is a matter of finding out what the appliance draws in normal use and use a fuse that is, say, 25% heavier to allow some headroom so the fuse doesn't run hot under normal use.

If there isn't a plate on the appliance showing what the voltage and current ratings are you would need to measure the current flow with an ammeter after the rest of the restoration is complete.

No, their are no indications anywhere, in that respect, on the cover of this equipment, .

What I don't want to do is run this device to find out what it draws, before it is restored. Such a reading may well be unsafely abnormal.

I'm surprised that Heathkit never incorporated fuses in their kits. Surely this potentially left them open to massive claims for injury or death..


Thanks

Hi, start off with a 2amp fuse in an approved holder. That's small enough to pop with a shorted rectifier or a short from a dud switch or crappy wiring insulation.
That's for short protection to avoid burning wires.
Then measure normal current and do what Brad suggests.
That size then may give you some 'overload' of component protection without nuisance blowing.
When I scratch build a radio or power supply I start with 2 amp and then figure out if I have to go up or down or fit fast blow/slow blow depending on start up surges. Measure that with a peak hold meter or just watch the digits/needle fly on an ordinary meter.
Make sure the 240 cord is a 3 wire earthed green/yellow cable, not the twin flex supplied in the original kit.

Cheers, Fred.

I'm surprised that Heathkit never incorporated fuses in their kits

I'm not. Americans hardly ever put fuses in their tube equipment. I have a 30 valve Hammond organ that had no fuse in it.

The first thing I'd do with that unit is to re-cap it. Also, if the rectifier is a metal type (selenium or copper), I'd replace it with silicon. If anything is bound to let the smoke out it's one of those, and it's foul-smelling poisonous smoke, too.

I design electronic gear and I never use conventional fuses. Reason: A fuse that's small enough to blow under fault conditions will nuisance-blow repeatedly in service.

Back when I serviced B&W TVs under warranty, failure of the mains fuse was by far the most common fault.

With a small transformer and a 2A fuse, the transformer will.burn up before the fuse fails.

Best solution is a thermal fuse in the transformer winding. And a power supply with cycle-by-cycle overcurrent protection.

Best solution is a thermal fuse in the transformer winding.

I agree. Second best (for vintage gear) is sacrificial resistors.

In silicon circuits, oftentimes the transistors blow to save the fuses.

I have ascertained from the Heathkit IG102 schematic that it uses a maximum of 20Ma.

I have setup a fuse for this signal tester, & although I would have preferred more headroom, the only fuse available to me at present is a 31ma slow blow fuse.

This glass 3AG fuse contains a 330 ohm resistor but I cannot test it for continuity, as can be done for straight wire fuses of higher value.

Although visual inspection seems to indicate it is not fused, is there any way (out of circuit) to test for continuity & which way should the fuse be loaded into the fuse holder (resistor towards circuit or the reverse)?

Check continuity with an ohm meter. If it reads 330 ohms then there's continuity.

Fuses are not polarised, so connect it in either direction.