Marshall TSL JCM 2000 blows a fuse when turned up past 6!

[Kyuss]

Hi guys,
Wondering if you can help me?
My TSL blows the fuse whenever i turn it up past 6, im using s a pedal board with a Jackhammer and a Fuzz Face but it will not have anymore input after 6 on the clean channel with the pedals through it.
I'd understand if i was cranking it up to 10 it would give up but i dont play venues that always have a good P.A and bought this for the power at big volume.

Im not having it insanely loud but it just dies when its past 6 and i have to replace the fuse.
Any help would be much appreciated.
Thanks for you time to read this

[Jazz P Bass]

My guesses are:
- the wrong value/ type fuse
- a bad power tube.

[Kyuss]

Hi,
Im using the T1A 250v slowburning fuse that it recommends on the back of the head, so you think it could be the power tube? thanks so much for the qick reply

[Enzo]

Have you tried the amp through a different speaker AND a different speaker CORD? And are we using a real speaker cord and not just a guitar cord to connect head to cab?

A speaker that opens its voice coil past a certain cone excursion could cause problems, as could a bad cord or other wiring problem in the cab.

[Kyuss]

Hi,
Yes i have 2 cabs which it happens with both, tried different speaker cables to (not crazy instrument leads, even i hate it when i see people doing that!)
Thankyou so much for you quick replies

[Gtr_tech]

Its blowing the HT fuse so that points to either output tubes or pwr supply. Has the bias for the output tubes been checked?

[soundguruman]

Hi guys,
Wondering if you can help me?
My TSL blows the fuse whenever i turn it up past 6, im using s a pedal board with a Jackhammer and a Fuzz Face but it will not have anymore input after 6 on the clean channel with the pedals through it.
I'd understand if i was cranking it up to 10 it would give up but i dont play venues that always have a good P.A and bought this for the power at big volume.

Im not having it insanely loud but it just dies when its past 6 and i have to replace the fuse.
Any help would be much appreciated.
Thanks for you time to read this

It points to two things really...
1. First, your speaker impedance is suspected as wrong, and it causes the amp to draw too much current. Miscalculation of speaker load is a very common mistake. Also, a blown or damaged voice coil, or a bad, improper, or damaged speaker cable is not uncommon either. Related to this is setting the impedance of the amp to the wrong setting.
2. The bias of the amp is suspected of being adjusted improperly. If the amp is too hot, the fuse will blow when the amp is pushed hard.

Replacing the fuse over and over when it blows will damage the amp, transformers or tubes. Go back to the start, as above-- and eliminate all possible causes before trying to operate the amp again.

[Steve Conner]

All valid points that should be checked out.

But it could also simply be a bad power tube that breaks down and arcs at high power. When were the tubes last replaced? Has it been on the road a lot, bashing around in car trunks and so on?

[The Dude]

Certain serial number JCM2000's (don't recall which) had an under-rated cap at C46. It should be 22pf/500v. It's located by one of the end power tubes and it's for anti-oscillation. I've seen this cap cause your problem a number of times. I usually just replace it if I open one of these up to be sure (with a 1kv rated cap). You can chase this problem for hours because the cap will usually test ok.