Add HT fuse to Dumble

[frusciante89]

Hello everyone, I have a question on HT fuses. Dumble didn't to put one in his design, but I'd like to add one to my clone for extra protection. Will the attach diagram be a good way in your opinion to upgrade to Mains + HT fusing?

[Bombacaototal]

HT fuse should be 1A for 100W amp. I had 0.5A on my SSS 002 and caused a lot of issues

[pompeiisneaks]

I don't think you're supposed to add a CT to a Bridge Rectifier like that. It's bad news. You should add the HT fuse inline between the rectifier diodes and the Standby switch, or after the switch, I'm not sure if the inrush current there will be a problem or not, though.

~Phil

[martin manning]

Phil, I don't see a bridge, it's a two-phase rectifier.

See here for discussion on fusing the HT: http://www.valvewizard.co.uk/fuses.html

In addition to not protecting the transformer against shorted rectifier diodes, fusing the CT on a transformer with a bias tap will damage the caps in the bias circuit if the fuse opens.

[pompeiisneaks]

Oh I do that a lot... sorry, I see multiple diodes more than a single per side I let my brain melt and forget that you need a 0 ref for it to be a bridge. This is just extra diodes in case one fails short.

Sorry nothing to see here, move along lol

~Phil

[timrobertson100]

In addition… Since you have 240V on that diagram you may be in the UK. If so, I believe your power switch should be a double pole and also switch the neutral. Perhaps someone could confirm that?

[frusciante89]

There was a typo in my original diagram. I went back to it and modified it accordingly. This is how I'm thinking about it - keep in mind I'm assuming a PT with center-tapped HT.
Would this be in line with modern safety standards?

[fred.violleau]

Looks good to me!

Fred.