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Hey guys.

I was at band practise earlier and while I was playing, my Marshall JTM60 combo just cut out. The mains power was still there, it just lost all sound.

I looked around the back and 1 of what I believe to be the power valves was glowing immensely (more than the other power valves) and was extremely hot. So I turned the amp off, unplugged it and left it alone.

I've noticed over the last week or so that my 60w valve combo has had trouble keeping up with the other guys Peavey Bandit or 40w Marshall valvestate combos, so I figured it was maybe ready for a new set of valves.

Does this sound like a symptom of being a valve problem? If not, what could it be and what should I do about the amp?

Thanx for any info.

Craig

There are fuses a bit hidden in that amp. At least 2. You have to yank the chassis out to get to them. I would try that first.

Danger Will Robinson, high voltages at play here. Enought to send you off to that quot;long sleepquot;, if you know what I mean.


Originally Posted by wixedmordsThere are fuses a bit hidden in that amp. At least 2. You have to yank the chassis out to get to them. I would try that first.

Danger Will Robinson, high voltages at play here. Enought to send you off to that quot;long sleepquot;, if you know what I mean.

Hi there.

Thanx for your reply

To be honest I don't really want to be taking this amp apart myself because I know i'd either make the problem worse, or kill myself in the process I'm not the best guy when it comes to work such as this.

Craig

Craig,

You know a healthy JTM60 is WAY louder than a Bandit or a 40w Valvestate.

I reckon an output valve died and you've been running on just one for a while. There are only 2 power valves in a JTM60 - the big ones (EL34s). Are they both glowing? (Take the black metal grille thing off if you can't see properly). An EL34 died in my JTM60 once and the symptom was a sudden drop in volume.

Power valves and fuses are the obvious things to check/change, but if that doesn't work it might be best to see a tech.

Simon

It's not a fuse. If the fuse had blown, the amp wouldn't power up at all. That's the point of having a fuse.

I'm guessing that it's a tube (valve) problem. $20 should get you up and running again. It could be something more sinister, but I doubt it. It needed new tubes (valves) anyway, so start there.


Originally Posted by HamerPlyrIt's not a fuse. If the fuse had blown, the amp wouldn't power up at all. That's the point of having a fuse.

I'm guessing that it's a tube (valve) problem. $20 should get you up and running again. It could be something more sinister, but I doubt it. It needed new tubes (valves) anyway, so start there.

Ah, HP, not true. There are fuses on board in this one. I have one, and it did this same thing.

Not talking about the main fuses.

But, a tube is easier to get at.


Originally Posted by HamerPlyrI'm guessing that it's a tube (valve) problem. $20 should get you up and running again. It could be something more sinister, but I doubt it. It needed new tubes (valves) anyway, so start there.

This tube/valve thing is hilarious. Let's call the whole thing off.


Originally Posted by Simon_FThis tube/valve thing is hilarious. Let's call the whole thing off.

Exactly. Everyone knows quot;tubequot; sounds better than quot;valvequot;


Originally Posted by Simon_FThis tube/valve thing is hilarious. Let's call the whole thing off.

You say potato...

I say tomato

Two different fuses, huh? Why?


Originally Posted by HamerPlyrTwo different fuses, huh? Why?

One's a heater fuse. I am not sure about the other. They are in a fairly hard spot to get at, but not impossible. It is a complicated amp to work on.

Respect given HP. Just trying to help the original poster.

No, no... I appreciate the correction. I'm just surprised, I've never owned an amp that had two fuses.

It's a stinker, 2 on the board, 1 in the mains.

Actually, a lot of ampegs come with 3 fuses, mains, and 2 heaters... as well as some other amplifiers, it is done to protect the tubes. You will probably be looking at another problem if the heater fuse blew as in most cases(over 50% of which) there is an underlying internal cause to a blown fuse. Take it to a competant tech(which are hard to find) and let them take care of it. Youll save time and your life possibly.
IMO, you should, if not properly trained and educated, take it to a tech. I have see too many hack jobs in my shop which have cause much greater problems then the original cause. You will probably save money in the end.

As wrong as I was on the fuse thing, I still say to replace the power tubes. Even if it doesn't fix the problem, you end up with a pair of spares that you should have anyway.


Originally Posted by bvc310Actually, a lot of ampegs come with 3 fuses, mains, and 2 heaters... as well as some other amplifiers, it is done to protect the tubes. You will probably be looking at another problem if the heater fuse blew as in most cases(over 50% of which) there is an underlying internal cause to a blown fuse. Take it to a competant tech(which are hard to find) and let them take care of it. Youll save time and your life possibly.
IMO, you should, if not properly trained and educated, take it to a tech. I have see too many hack jobs in my shop which have cause much greater problems then the original cause. You will probably save money in the end.

this week, i say a $30 dollar repair turn inot a $250 repair all beucae the owner decided to cheap out and not fix teh original problem(a blown voice coil and dead tube)

Thanx for the replies guys

I thought something may be wrong when I started getting overpowered by a Peavey Bandit Originally Posted by Simon_FI reckon an output valve died and you've been running on just one for a while. There are only 2 power valves in a JTM60 - the big ones (EL34s). Are they both glowing? (Take the black metal grille thing off if you can't see properly). An EL34 died in my JTM60 once and the symptom was a sudden drop in volume.

When I last had the amp switched on, from what I remember only 1 of the power valves was glowing, but it was glowing much brighter than it had before. It was almost like someone was shining an orange torch into the back of my amp!

IF I do decide to try new power valves, will the amp not need biasing etc? I've never dealt with valves etc before, so I don't really know what I have to do or what valves to use as replacements etc.

Thanx for the advice

i had the same thing happen to my JTM60 after i had bought it. they ended up fixing the OT.

i had so so so so so much trouble with that amp and i thank god sold it.

i dont want to turn you off and the amp sounded pretty darn good when i first got it. but after awhile after fixing it all the time, it lost tone.

my best experience was putting 6L6's in it. try it, i thought it sounded way better.

but i sold the sucker and it was the best thing that happened to me.


Originally Posted by BrowIF I do decide to try new power valves, will the amp not need biasing etc? I've never dealt with valves etc before, so I don't really know what I have to do or what valves to use as replacements etc.

Biasing isn't essential on every valve change, especially if you replace the valves with the same brand/spec as the ones that are in there. Having said that, with the problem you're having it's probably a good idea to get the amp checked over by a tech anyway, in which case you may as well get the bias checked/set. The EL34s that come stock in Marshalls are usually Svetlanas, but often Marshall-branded. You can buy the Marshall-branded EL34s in pairs from Marshall dealers.

Thanx for the posts guys

I'm going to buy some replacement valves myself, and then get the amp looked at by a good tech. That way I know I'm not being overcharged on valves etc

I've been contemplating selling the amp for a while, but I'll see how I go with it once it's fixed.

Craig