H.T fuse?

lukedlb

Out of curiosity, what does h.t stand for on my amp? There’s also a mains fuse. 

lukedlb

High tension?
the 3A mains fuse blew the other night. I’ve replaced an old mullard with a gold lion and the fuse. So far so good. 

springhead

Yes, High Tension.  So somewhere on the other side of the power transformer from the mains fuse and in the high voltage supply to the valves.

lukedlb

Thanks @springhead ; ;
would blowing the mains fuse over the ht fuse indicate one problem over another?

jpfamps

lukedlb said:

Thanks @springhead ; ;
would blowing the mains fuse over the ht fuse indicate one problem over another?

Depends where the HT fuse and it's type and rating.

As a general rule HT fuse blowing is caused by a power valve shorting (although it can also be caused by an output transformer short, and depending on it's position a rectifier or filter cap short).

The mains fuse blowing could still be caused by a valve short, but also by a mains transformer short, short on a transformer winding other than the HT winding.

I like to use fast blow HT fuses after the main filter cap. With fuse placed here a valve short will quickly blow the fuse.

Some manufacturers put the HT fuse before the rectifier and filter cap on the HT winding. Here you have to use a slow blow type, and often a valve short blows the mains fuse before the HT fuse.

rico

I have an amp that kept popping the HT fuse - turns out the output transformer is borked.

ecc83

"Our" S1 200 has a 1A QB in the anode only supply but it is a bit pointless because when the bad batch of 88s were dying the 'Purple Death', that blew, overall slo-blow HT blew, mains 3.15A T blew AND quite often the 13A in the plug!

Of course, when it came in NONE of the fuses were of the right rating or speed as a rule save perhaps the 13A.

Nice of course to close fuse things and properly protect them but the punter will defeat you every time!

IMO amps should be sold with fuse 'kits'.

Dave.