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Discussion Starter #1
I've recently bought a Canadian edition, Marshall JCM 800 2210. That's the two channel version.

I've loved the amps tone since I got it but have had a couple issues. I've found that when I really drive the amp it gets very hot and just turns itself off. I have to let it cool down, then press a switch in the back to reset the amp and allow me to play it again.


Recently I was recording with the amp and because it was just a ghost track I was just going through the di output and was not plugged into a cab. It was getting hot and shutting off multiple time until one of the tubes started glowing electric blue and blew.

Is it likely that it was cause by not plugging into a cab, is it normal, will there be any other damage done to the amp other than having to purchase a new set of tubes.
 

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WOW! I'm surprised it lasted as long as you say it did! Just turning an amp on without a speaker attached is enough to blow the amp up ... tubes, other components around tubes due to arcing, tube sockets, output transformer ... etc. NEVER run the amp without some type of load attached (speaker or a power attenuator like a THD Hot Plate). I would take the amp to a good tech and cross you fingers hoping it is just the tubes (not likely unfortunately). Sorry I don't have better news to tell you.
 

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Classic mistake - you're not alone!

iggs said:
WOW! I'm surprised it lasted as long as you say it did! Just turning an amp on without a speaker attached is enough to blow the amp up ... tubes, other components around tubes due to arcing, tube sockets, output transformer ... etc. NEVER run the amp without some type of load attached (speaker or a power attenuator like a THD Hot Plate). I would take the amp to a good tech and cross you fingers hoping it is just the tubes (not likely unfortunately). Sorry I don't have better news to tell you.
I had the same problem in for repair last fall! A JCM800 from a local studio where the bonehead owner knew just enough to wire in his own DI output. Unfortunately he didn't know that tube head MUST have a speaker load! He let his customers wail away for hours with no cab, just the DI to his board. The poor amp eventually died.

Of course, he didn't tell me what happened. To be fair, he didn't really know what he had done. So I find some fried output tubes and replace 'em. They biased up ok and things seemed fine until I plugged in a guitar and turned up the volume control. Soon as I got past '2' lightning started flashing out of the output transformer!

We spent extra on an upscale aftermarket output trannie. The bill was over $300 CDN by the time I gave it back to him.

Lots of other guys have made your mistake. Fortunately you came here for help and learned before too much harm has been done (I hope!).

PLEASE take your amp to a tech toute suite! And make sure he checks the bias idle current while he's at it.

Wild Bill/Busen Amps
 

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Yikes, you are riding the edge of disaster there. Bill's right, get it looked at right away. I just fixed to Marshall AVT 100 heads for a kid around here. The goof was running both heads into one cab. Needless to say neither amp fared well out of the deal.

Always use some kind of power atten. or if you want to do two heads into one cab, buy an amp switcher (or make on if you can) that has a built in power atten. If I use a DI and no cab, I've got a Leader 150 watt dummy load that can be set to 4, 8 or 16 ohms. It's a piece of test equipment but works well.
 

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Discussion Starter #5
Is there a way to find out if I caused any real damage?

I was looking on one site that said to check underneath the tube that blew to check if there was any burn markings which there were none.

I'm obviously not going to turn my amp on a again right now and I left my cab at the place where I'm recording and intend to take my amp in as soon as I can.
 

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Try it!

Chowbot said:
Is there a way to find out if I caused any real damage?

I was looking on one site that said to check underneath the tube that blew to check if there was any burn markings which there were none.

I'm obviously not going to turn my amp on a again right now and I left my cab at the place where I'm recording and intend to take my amp in as soon as I can.
When you plug your amp properly into a speaker cab if the amp sounds ok then it probably is!

Output transformers are simple, tough critters. They usually are either ok or "snackered", no in between. Your EL34's may be punched. If the fuse blows try replacing them. If it blows again you've got more serious problems.

Even if the amp seems to work fine you've probably taken a lot of months off the life of those tubes. When you get new ones be sure and have the bias adjustment checked/set at the same time.
 

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Discussion Starter #7 (Edited)
Well I'm probably going to take it in next week to get it repaired and completely change all the power tubes.

The thing I can't believe I forgot to mention was that... well after the tube blew it wouldn't turn on again at all.. Know why this is?


Edit: Because this just worried me so much I took the risk and turned it on without a cab just for a second to see if it would even work. Luckily the red power light came on and I shut it off. So my situation isn't that bad.

I'm still worried that the tube blew.. it was glowing electric blue. How do I know if it is blown.

And I should be taking my amp in on tuesday to get it checked and have all the power tubes replaced. What should I specifically tell them to do?

And thanks guys, first time on this forum and you guys are a great help.
 

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Chowbot said:
What should I specifically tell them to do?
Don't just go and say: "My amp is not working". Tell them EXACTLY what you did and what caused the damage. Don't be embarrassed, we all make mistakes, they just need to know what to look for.
 

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Discussion Starter #9
Ok, hopefully I don't have to keep doing this.

I finally tried the amp out again (through it's cab this time) and it was working fine, higher volumes sounded good. No crackling, channel switching was fine and tonal qualities were all just as good.

One major thing though, the tube second from the right was glowing blue and getting more and more intense. I thought it would be best to ask questions first and save myself a lot of gried. This is the same tube that gave me problems before and it was only that one. What could that be?
 

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Discussion Starter #11
I'm taking it tomorrow, I just wanted to turn it on briefly to make sure it still could turn on at all and to gauge how bad the damage was.

So I'm guessing you have no idea what the tube glowing blue meant?
 

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Chowbot said:
So I'm guessing you have no idea what the tube glowing blue meant?
Other then that something is definitely wrong ... no. Maybe (for whatever reason) the tube is getting way more voltage then it can handle, or maybe the tube is blown and is now operating in an abnormal way. I know a lot of "theory" about tube amps and electronics in general but not enough in practice to be able to trouble shoot it.
 

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"Blue, navy blue. I'm as blue as I can be..."

Chowbot said:
I'm taking it tomorrow, I just wanted to turn it on briefly to make sure it still could turn on at all and to gauge how bad the damage was.

So I'm guessing you have no idea what the tube glowing blue meant?
Lots of tubes have a LITTLE bit of blue or violet glow inside. It's caused by a few atoms of gas left in the tube's vacuum that glow like a neon light from the high voltage inside a working tube. That much glow is nothing to worry about. Even some new tubes will have a bit of this glow.

If you get a LOT of glow that's a different story. I'm talking a glow that seems to fill half or more of the inside! This usually means the tube is half fried internally. Little grid wires melting and/or the coating on the cathode boiling off results in a lot of those gas atoms and then you get way too much glow.

The good news is that this may mean the only thing damaged is the tubes. That's the cheapest scenario possible!

Sounds like you were lucky.
 

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Discussion Starter #14
Yep, and that's just how it turned out. My first two power tubes were almost completely gone which was causing my amp to short and shutting itself off.

No other damage was done so now I have 4 new tubes which are biased and a fully functional amp.

Thanks for your help everyone.
 
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