Mesa Dual Rectifier red hot tubes and blown fuse

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user 35785

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I was recording guitars for a little while today and heard the 'clinking' sound that the tubes usually make when they first warm up. I thought it was odd since it was on for a whole hour so I went over and checked, and saw the power tubes were red hot and something inside smelled like burning plastic. I shut the amp off, waited a minute, then turned it back on, same thing. The volume dropped considerably, which made me wonder if the speaker cable was bad. When I twisted it to see if it was connected properly, the fuse blew.

I am seriously hoping that the problem is only just a bad speaker cable (its a cheap stagemaster 15' speaker cable that I bought maybe a year and a half ago), and not a bad capacitor or output transformer.
Last year my amp had issues with the gain and tone knobs, so I sent it in to a tech. He told me that the capacitors on several of the knobs were bad, and he replaced them. I don't remember exactly what he said at the time, but I wish I did though, because I think he said that he only fixed what he could to fix the problem and that the amp would need to be recapped if I plan to push the volume far beyond "bedroom" levels. I told him that I use the amp just for recording, and he said I shouldn't worry about it, but I REALLY hope that a capacitor didn't go out on me, since hes the only tech in my area and (naturally) charges insane fees for his services.

I'm not at all prepared to recap my amp, which really worries me since now that I think of it:
- I have a minifridge in my room that apparently draws alot of power. When it kicks on, all the lights dim a bit for maybe a quarter of a second, and if I'm recording at the time, loose a little bit of volume for a second. I don't have it on any surge protector or power conditioner, but I do unplug it whenever I dont
plan on using it for a while and during thunderstorms. Is this hard on the output transformer?

- I found out that engaging the FX loop, turning down the send volume, boosting the mix volume, then cranking the master volume gave the amp a more "thicker" sound and took out most of the fuzzy characteristics. I did not have any send/receive cables connected though, and the output volume was only at 9 o'clock. I knew it was harder on the tubes, but they didn't act weird until today, and when I set the loop back to bypass the tubes didn't change.

The tubes on the amp are pretty new, they are about a month old. I didn't bias the amp because its fixed and I have no way of changing it, and I didn't have any odd problems with the tubes I put in before, and always use JJ 6L6GC. I know I would ideally need to adjust the bias at some point, but I don't think bias is the issue here.

While I'm out buying a new fuse I'll try to find another speaker cable to see if thats the only issue (fingers crossed)
Any recommendations while I'm out there?

Thanks
 
:cry:

This blows. I'm not really sure what to say.

My first suggestion is to remove the amp from the headshell and look at the insides. Look for any melted or burnt components or burnt sections on the circuit boards. I suspect that the power tubes were malfunctioning so the screen resistors might be cooked.

If everything looks fine, you can always chance putting in new tubes and a new fuse and powering your amp up. It just seems like a waste of $$$s to go this route given the history of the amp. If the Tech is THAT concerned about your amp, it is likely that you can no longer procrastinate on this major repair.

I'll wait for some more experienced members to contribute but my current thoughts are:

1) send this into Mesa (If Possible)

2) Find another used one in a good state of repair. I've heard of the original 3 channel model going for $900 or even in some cases, as low as $700. $350 cab job vs $700.
 
As Yellowjacket had said, if it is at all possible, I'd send it in to Mesa. They are the experts... hell, they built the amp! Though, if you cannot send it to them, I'd mail it to someone who can really do it well. I had a friend who sent an Uberschall out to someone in Nevada, and we live in NJ! I can't remember who the guy was, but the guy fixed the amp's problem, which turned out to be the transformer, and it sounded like heaven afterwards! Anyways, I'd do some research on dudes who could fix it. Look for good reviews. If it takes the long wait and a long time to fix, it may be worth it. Though, again, as Yellowjacket said, given the amp's criminal records, you may have to consider a replacement.
 
Sounds like one of the power tubes may have failed. You'll sometimes get popping noises if one of the internal components comes loose and gets bounced around by the vibrations, which will eventually lead to red plating once the componant shorts something inside the tube, which will usually blow the fuse to protect the amp. Just because they're fairly new doesn't mean they won't fail... it's one of the realities of maintaining tube amps.

The burnt smell may just be due to the super heated tube cooking dust and/or finger oil. It may also be something else, but lets hope not.

If you still have the old power tubes and they were still serviceable before you replaced them then put them back in and replace the fuse. If the amp works then one (or more) of the new power tubes went bad. If the old tubes red plate and the fuse blows again then send the amp to a tech.

If you don't have old tubes then pick up a set of new tubes. If you feel the speaker cable is of dubious quality then play it safe and replace it.
 
screamingdaisy said:
Sounds like one of the power tubes may have failed. You'll sometimes get popping noises if one of the internal components comes loose and gets bounced around by the vibrations, which will eventually lead to red plating once the component shorts something inside the tube, which will usually blow the fuse to protect the amp. Just because they're fairly new doesn't mean they won't fail... it's one of the realities of maintaining tube amps.

The burnt smell may just be due to the super heated tube cooking dust and/or finger oil. It may also be something else, but lets hope not.

If you still have the old power tubes and they were still serviceable before you replaced them then put them back in and replace the fuse. If the amp works then one (or more) of the new power tubes went bad. If the old tubes red plate and the fuse blows again then send the amp to a tech.

If you don't have old tubes then pick up a set of new tubes. If you feel the speaker cable is of dubious quality then play it safe and replace it.

I still say open it up FIRST before doing anything and don't spend any $$$s you don't have to. If things look sick on the inside of the amp, might as well think about taking it to a tech (Like Mesa's repair shop) or replacing it. I'm just really concerned about what your tech said about the filter caps, it seems odd to me. How old is the amp? My DR is almost 20 years old now and I haven't had any trouble with it.
 
Ok got a new speaker cable, and now I can play the amp, but when I start raising the volume the tubes start heating up and the fuse blows.
It does the same thing with the old tubes that I had, and with he power on spongy rather than bold.

Only the power tubes glow red, the rectifiers and preamps are all good. Does this mean I have a bad output transformer? I can play the amp at low volumes without blowing the fuse and it sounds fine
 
Hoboy.

Call Mesa.

I mean it **could** be the tubes but based on what your Tech said, it could very well be something else and this is what I'm concerned about. You should assess if it is cheaper to get the amplifier repaired or to get it replaced, and Mesa can assist you with this. Do you remember EXACTLY what your tech said the problem was?
 
@ Yellowjacket

I opened it up and everything looks pretty good, at least to me knowing nothing about the inner workings of amps. I don't see any obvious burns, bulging/leaking/cracked capacitors, or fried resisters. Is there a way to post pictures on this forum?


@ Lespaulguy

The serial number is R-016345, and I'm pretty sure the OT is original.

I'll give mesa a call and see what they say
 
OK, this thing is a fairly recent amp. We're talking max 10 years old, I guess.

Yes, I say call mesa. If it wasn't for the history of the amp, I'd immediately blame the power tubes and be done with it. The way you're describing the problem, it sounds like a tube issue. It's just the 'history' of the amplifier makes me nervous. Is there any way you can get the tech to EMAIL you what the problem is? I mean even if you have to pay him $10 or $15. Then you can talk to Mesa about it.

My thoughts are to run the problem by them and find out how much it costs to get it fixed. You can factor shipping / shipping insurance in as well, and then figure out if it is worth it to get it fixed or to simply buy another one.

If you spend $120 and a few dollars on fuses and then you cook all of them and blow up your amp, you risk pissing money away AND further damaging the components of your amplifier. Talking to Mesa FIRST at least gives you an idea what is going on, and it's free. You just need to know from the tech what you are talking about so Mesa can advice you appropriately. Without that information they'll assume the same thing everyone would, that it's simply a tube problem. Most Mesa amplifiers are extremely robust and last a LONG time before something major ever goes wrong.

In the event you decide to replace your amp, perhaps you could sell it to the tech at a discounted price to recoup some losses that way as well.
 
...I'm a little embarrassed...

I was about to call mesa and buy a new mercury output transformer I found one last replacement tube for my amp. I then realized that when I was troubleshooting I was always using the silicone diode rectifiers, not the tube rectifiers. When I start cranking the volume with the tube rectifiers live I noticed the power tubes plates looked normal, but one of the rectifier tubes started getting red. When I took a closer look, it erupted in a huge lightning show. It started arcing like mad. On top of that, all the lights in my room started flickering. I immediately shut the amp down and took the rectifier tubes out.

I have even less knowledge about how tubes work, so please bare with me. When I shake the tube it sounds like a broken light bulb. Two of the little white things that glow gently as the amp is warming up (heaters?) look like they just exploded. I'm now punching myself because I never replaced the rectifier tubes in the few years I've owned this amp, and when I bought this amp the tubes looked like they have never been changed. I replaced every tube except for the rectifiers because I always used silicone diodes, and thought that they bypass the 5U4G tubes.

I'm ordering new ones now. Could this really come down to a bad rectifier tube?
 
Shudder said:
...I'm a little embarrassed...

I was about to call mesa and buy a new mercury output transformer I found one last replacement tube for my amp. I then realized that when I was troubleshooting I was always using the silicone diode rectifiers, not the tube rectifiers. When I start cranking the volume with the tube rectifiers live I noticed the power tubes plates looked normal, but one of the rectifier tubes started getting red. When I took a closer look, it erupted in a huge lightning show. It started arcing like mad. On top of that, all the lights in my room started flickering. I immediately shut the amp down and took the rectifier tubes out.

I have even less knowledge about how tubes work, so please bare with me. When I shake the tube it sounds like a broken light bulb. Two of the little white things that glow gently as the amp is warming up (heaters?) look like they just exploded. I'm now punching myself because I never replaced the rectifier tubes in the few years I've owned this amp, and when I bought this amp the tubes looked like they have never been changed. I replaced every tube except for the rectifiers because I always used silicone diodes, and thought that they bypass the 5U4G tubes.

I'm ordering new ones now. Could this really come down to a bad rectifier tube?

I hope so.

Just about a month back, my amp started flashing and the fuse blew. I replaced the rectifier tubes and it started working again so it is entirely possible that this is the problem. Check it out, but still give Mesa a ring. I'm curious what your tech was saying the long term problem was.
 
Ok listen closely (this is probably is the problem)... Open the amp up and look at the SCREEN GRID RESISTORS. They are little black resistors right by the power and rectifier tubes. You said you smelled burning plastic so I bet you one of them is burnt. Look real close at all resistors by the power tubes. My amp did same thing years ago and new tubes fixed it for a bit, but then the lightening bolts in one tube went off, opened amp up and seen one of the screen grid resistors were fired. If so replace the resistor and make sure to CLEAN ALL CARBON BURN SPOTS OFF THE PCB board. Open it up again and look real closely at all the resistors by recto and power tubes. Screen grid resistors protect tubes from blowing. I bet that's it.

Or just sent it to Mesa cause I had mine fixed by a "Mesa certified" tech and he changed resistor but didn't clean the burn spot off board, which is VERY important. Just send to Mesa if your not experienced. Mesa amps are tricky to work on if ur an amature. Good luck and DONT PLAY OR TURN ON AMP AGAIN UNTIL FIXED.
 
Ok replaced the rectifier tubes. Now it doesn't blow any more fuses, but the tubes still are red hot

I figured out how to post pictures:

http://s1274.beta.photobucket.com/user/qwertyuiop1944/media/IMAG0377.jpg.html?sort=3&o=0
http://s1274.beta.photobucket.com/user/qwertyuiop1944/media/IMAG0376.jpg.html?sort=3&o=1

EDIT

I think I found the problem:
http://s1274.beta.photobucket.com/user/qwertyuiop1944/media/IMAG0379.jpg.html?sort=3&o=0
 
Wow, dat glow! :mrgreen:

What was wrong with the part in the circle? I'd like to know what made your recto cooking.
 

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