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Amp fusing?

I am currently building a tube preamplifier kit from Ali. There is little in the way of instructions and after looking at several other circuit diagrams of other boards/kits I was wondering why there is mainly only fusing on the transformer primary and nothing on the seperate transformer secondaries. Are there issues with adding fuses on the secondary supply's?

Thanks

3 answers0 replies

3 Comments

Bob cooke

Apr 10

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Check this article. https://www.valvewizard.co.uk/fuses.html

Junkman George

Apr 11

Replying to

From the linked article:

"Fuses are not precision devices; they melt fairly slowly during faults, taking many milliseconds to whole minutes to blow, depending on the level of overload"

Making them virtually useless to prevent component failure. Your regular mains fuse would/should protect the transformer.

Junkman George

Apr 06

In some places (but not all) fusing on the primary side are part of the electrical code/insurance requirements. I'm guessing they don't want the transformer turning into a toaster oven and burning down your house?

Fusing the secondaries has very limited value because usually the damage is done before the fuse blows. I had a high power transistor amp once where the secondaries were fused, all for nothing, as usually the output transistors failed first, then blowing the fuse.