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Hey all

HT fuse in my JTM has blown. Suspect power tubes or a filter cap (based on previous experience only, not really sure).

Anyone know any good tube amp techs in the Manawatu area? I usually use Brodie at MDR but i think hes away and i want to get my amp up and running again.

Put a fresh fuse in and try it again. If it blows change the power tubes and try a new fuse again, if blows again go to a tech.

If the HT fuse blew while you were running the amp hard, it would be the output tubes. Make sure you replace the whole set (with a matched set). Don't just replace 1 tube - that's asking for trouble in a JTM. Check the screen resistors too (although the Welwyn 7Wers are pretty robust and its not normally a problem). If you want output tubes to last in those, don't bias them too hot. Bias them just over 50%. Doesn't matter if you get a crossover notch - you won't hear crossover distortion when its cranked anyway. Modern production EL34s are a beaatch.

If the HT fuse blew on startup, it could be a filter cap problem (but the mains fuse should also blow if there is too much current draw from a failed filter cap)

My big tube amp won't work if I plug the pedal board into the front but does when I run it through the effects loop.

Why is this? Cheers.

foal30 wrote:My big tube amp won't work if I plug the pedal board into the front but does when I run it through the effects loop.

Why is this? Cheers.

Does a guitar direct into the front work?

Yes.

I ask because I assumed pedal boards go through the loop however in the Bass world this isn't the reccomended thing.

It appears in my instance I have no choice lol

FX loop has an issue I expect. Depends on the design but some bypass the loop circuitry when nothing is plugged in, so if the circuit has an issue it will work when not in use.

sizzlingbadger wrote:FX loop has an issue I expect. Depends on the design but some bypass the loop circuitry when nothing is plugged in, so if the circuit has an issue it will work when not in use.

Thanks.

TBF I'm not 100% clear

try a patch lead in the loop in and out

mrmofo wrote:try a patch lead in the loop in and out

I had a amp where this was needed sometimes. If it “thinks” there is something in the fx loop but there is nothing, it may bypass the preamp.

Delayman wrote:

mrmofo wrote:try a patch lead in the loop in and out

I had a amp where this was needed sometimes. If it “thinks” there is something in the fx loop but there is nothing, it may bypass the preamp.

it depends on the amp, my Marshall likes a patch lead now and again. loosens the cobwebs, has a volume control for the loop, I`m not sure if that's a thing or not.