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Dear God, What Just Happened To My Amp?


StophJS
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Well, I believe my POD HD 500 may have just fried my Marshall TSL 100, or at least fried the tubes. 

I was running my POD into the amp via the 4 cable method. Had the loop level switch pushed in and volume set to about 6. This is the first time I've ever done this for more than a couple of minutes. It sounded excellent for about 20 minutes, and then I noticed a massive drop in volume. I went and looked into the grating on the top of the amp. Two of the tubes seem to be doing nothing, while one tube was burning extremely bright, and I noticed a distinct smell of burning that has now filled the room. Now when I just run a cable from guitar straight into the front of the head, I get absolutely nothing. Yes, I turned the FX mix down.

Can anyone please clue me in on what just happened?

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   You may have fried a tube socket. It has happened to me several times with Marshall heads. Take out the tubes (with the amp off & unplugged of course) and check the tube sockets (bases they plug into) for signs of arcing (brown or black burn marks). If one or more tube sockets show signs of arcing, it may mean other problems like a bad transformer or other component. You may just need the sockets replaced. Hopefully, if there are no burn marks on the sockets, a tube  may have just failed & you can just replace them. Did you check for a blown fuse? You may need an amp tech to look at it if it's more than a bad tube.

 

   I'm not sure how the POD could have caused that but if you had a line level signal plugged into an input that's expecting an instrument level signal, maybe that could do it. 

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This is not unheard of with tube amps.  I doubt the POD had anything to do with it.  As guitarno said, check for arcing and other signs of burnt components.  Be really careful when working on tube amps, capacitors can put out enough voltage, even with the amp unplugged, to cause serious injury.  If you don't feel comfortable doing this yourself, take it to someone.

 

How old are the tubes ?

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Thanks for all the input guys. I'd say the tubes are a good 8 years old. I have to say I find it a bit tough to swallow that the POD had ABSOLUTELY nothing to do with this failure. The amp has run fine for a decade, and it was just when I used the 4 cable method with the POD for the first time that this happened. The volume on the TSL 100 drops a lot though when running the 4CM, even with the FX mix cranked, so my amp volume was set quite a bit higher than it's used to. Some posters on the Marshall forum suggested that I overloaded the return input, and that it may well have been related to the pedal. Who knows... could be purely coincidence I suppose.

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The tubes are 8years old...there's your problem. Would you expect an incandescent light bulb to last that long?

 

Yes, you pushed the tubes further than normal by using 4cm.

No that's not the POD's fault.

More energy through the tube and you popped them.

 

Basic amplifier maintenance. You can't expect tubes to last forever.

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   Yes, 8 Years is normally way too long for tubes. It really depends on how many hours they have on them and how many times they've been turned on/off. An 8 year old tube with no hours or use may be in perfect condition, but if you're using you're amp a lot, replacing them yearly or less is not uncommon, depends on the hours. If this amp's been getting a lot of use, and the tubes are 8 years old it's amazing they haven't failed before. Your amp would probably sound better with all new tubes (good ones).

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The volume drop is what needs to be looked at as that is why you overcompensated on the master volume.

(after amp repair)

Probably the change was enough to finally end their life.

 

The Burning smell, probably arcing not uncommon. check it for dust too but when the tubes begin to fail the electrical current will find the path of least resistance.

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Tubes fail and 8 years doesn't tell the story.  How many power on hours?  When power tubes fail they often take out another component or the fuse if there is one.  Nothing you do to the input really can cause a good tube to fail like that.  You would kill the speaker long before you would kill the power tubes.

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