Fire!

[Dave S]

Originally Posted by Tom Albrecht

I do a lot of restorations for other people, and one modification I always do is to put in a line fuse. Stories like this one make me glad that I do. I also advise people never to leave antique sets running unattended.
I saw a newspaper article from Germany a few years ago where a house fire was caused by an antique radio. German radios usually had a line fuse, so even that will not provide 100% protection.

I always put in a line fuse. Also a three conductor grounded line cord. Some concessions to strict "originality" just seem obvious to me, especially when the set will be used by a non-technical person. One thing I *usually* do when restoring a vintage set (although sometimes I manage to forget) is to break the center tap connection to ground on the power transformer and install a small fuse in the circuit. The reasoning, as I was taught, is that an overcurrent in the B+ can damage the power transformer without drawing enough current to blow a fuse in the primary. I usually install a fractional amp fuse greater than or equal to about twice the maximum design current draw. I've never figured out how to account for the surge current as the filters charge, but I've never had a problem with that. Perhaps a timed relay that shorts out the fuse for a few seconds when first powered on then opens would be a good enhancement. But I've always been taught that a line fuse wasn't foolproof protection.

[tubesrule]

Originally Posted by Dave S

One thing I *usually* do when restoring a vintage set (although sometimes I manage to forget) is to break the center tap connection to ground on the power transformer and install a small fuse in the circuit. The reasoning, as I was taught, is that an overcurrent in the B+ can damage the power transformer without drawing enough current to blow a fuse in the primary. I usually install a fractional amp fuse greater than or equal to about twice the maximum design current draw. I've never figured out how to account for the surge current as the filters charge, but I've never had a problem with that. Perhaps a timed relay that shorts out the fuse for a few seconds when first powered on then opens would be a good enhancement. But I've always been taught that a line fuse wasn't foolproof protection.

Keep in mind Dave that unlike a solid state rectifier, the emissions on a tube rectifier will come up slowly, so there really is no power on surge to the filter caps. Going twice the rated current sounds just about right.

Darryl

[pallophotophone]

Many years ago I had Sherwood tube type FM tuner that was on when I fell asleep.

The next morning I awoke and was dizzy and nauseous from the fumes from the burned out power transformer. The stench was awful !
Why it burned out was never determined.


BE CAREFUL OUT THERE !

Pallophotophone