Quote:
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.
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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