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Old 01-18-2011, 10:40 PM   #1
EvilAngel93
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Volume swells on tube amp

About ten minutes ago I was playing on my Mesa Rectoverb when I distinctly noticed a reduction in volume. It lasted for a little bit, then returned to normal, but then the volume diminished again. I tried using a different guitar, but still had the same issue. The power tubes have been replaced within the past year, but I'm not sure how old the preamp tubes are. What's the issue, and what can I do?
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My Gear:

-Custom Fender MIM Black Strat
-Mesa/Boogie Rect-O-Verb
-Schecter C-1 Hellraiser
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Old 01-18-2011, 10:48 PM   #2
jackson1040
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sounds like one of your power tubes are dying. look in the back of the amp when the volume dips again and see if you see the light one of of them is dwindling
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Old 01-18-2011, 10:53 PM   #3
M3lodeath
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oh the same is happening to me i need to replace one soon as well
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Old 01-18-2011, 11:03 PM   #4
EvilAngel93
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Really? Efff. I thought Mesa-brand tubes were actually good....how long are most power tubes supposed to last?
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Quote:
Originally Posted by Jackal58
I eat dead meat all the time. You don't have to chase it around your plate and it doesn't try to peck your eyes out.




It Happens.

My Gear:

-Custom Fender MIM Black Strat
-Mesa/Boogie Rect-O-Verb
-Schecter C-1 Hellraiser
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Old 01-18-2011, 11:28 PM   #5
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Quote:
Originally Posted by EvilAngel93
Really? Efff. I thought Mesa-brand tubes were actually good....how long are most power tubes supposed to last?


Nah, Mesa's are just rebranded tubes sold at a higher price, they're really nothing special. Buying from Eurotubes, Dougstubes, or The Tube Depot is always a better choice. Usually power tubes last about 2 years, give or take depending how much you play.
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Old 01-18-2011, 11:50 PM   #6
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They should last 1-3 years depending on how much and how loud you play. Mesa tubes are just rebranded Chinese ones that meet their spec. Ordering a set of Mesa spec tubes from actual tube stores will let you have nicer tubes that you don't have to mod the bias supply for.
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Old 01-19-2011, 09:36 PM   #7
stilt37
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Sorry for threadjacking, but I'm having the same issue with my little 5 watt blackheart amp.

One 12ax7 for preamp tube. el84 power tube. Replaced both of them today- volume still drops noticeably for a while and then comes back to normal for a bit.

Speaker maybe? Any theories?
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Old 02-22-2011, 10:47 PM   #8
EvilAngel93
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I'm bringing this back up again because the issue has returned. I checked the power tubes, but they seem to be working fine. Also, I have no idea how to tell if it's the preamp tubes. What else could be the cause?
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Quote:
Originally Posted by Jackal58
I eat dead meat all the time. You don't have to chase it around your plate and it doesn't try to peck your eyes out.




It Happens.

My Gear:

-Custom Fender MIM Black Strat
-Mesa/Boogie Rect-O-Verb
-Schecter C-1 Hellraiser
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Old 02-22-2011, 10:51 PM   #9
Kevin Saale
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Did you replace the power tubes? Thats probably your problem.
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Old 02-22-2011, 10:57 PM   #10
EvilAngel93
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Quote:
Originally Posted by Kevin Saale
Did you replace the power tubes? Thats probably your problem.


Nope. I've had my power tubes in for about a year but I haven't had any problems with them. I even checked for flickering when I was playing but, there wasn't anything I could tell, so I don't think it's the power tubes.
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Quote:
Originally Posted by Jackal58
I eat dead meat all the time. You don't have to chase it around your plate and it doesn't try to peck your eyes out.




It Happens.

My Gear:

-Custom Fender MIM Black Strat
-Mesa/Boogie Rect-O-Verb
-Schecter C-1 Hellraiser
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Old 02-22-2011, 11:00 PM   #11
BurstBucker Pro
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Not sure if it will help...

Taken from the link in my sig:

Speaking on how one might troubleshoot an unexpected change in volume...
benttop wrote: Not really enough information to make any kind of guess.

In my experience, you should expect a mechanical problem first, then a tube problem, then perhaps an oxidization problem (which actually is a mechanical problem).

Rule things out one by one. How did you rule out the guitar? Try another guitar, or try that guitar on another amp. How did you rule out the guitar cord? Try another cord or try that cord on another amp.

Look for the obvious - I've seen several reports of speaker terminals coming loose - look back there and see if yours are secure. And don't just look - give them a gentle tug to make sure they are securely fit to the terminal.

Get some DeoxIT and clean all the jacks on the amp, one by one, till you are certain this is not the issue.

Tighten your mounting hardware just for drill, simply because you're doing all of this maintenance right now. I don't see how this could cause the problem you have, but it could cause something later on.

Once you are absolutely convinced the problem is not mechanical, start investigating the tubes. About the only mechanism we have for doing that is substitution, so you're going to need a full set of tubes that you believe are good.

May as well start with the rectifier. This would not be a typical failure mode for the rectifier, but I've seen some pretty weird harold things and you want to be able to say you KNOW it's not the rectifier. And PAY ATTENTION to the key in the middle of the tube's pins. Modern rectifiers can go in wrong, despite having a key on that center pin. Sometimes putting it in wrong lets out the smoke!

Then try both power tubes with a fresh matched pair.

Then do the preamp tubes, one by one. Try the amp between each tube change. You might want a pot holder because it takes a long time to do this with hot tubes unless you can pull them right out.

Do NOT just replace all the tubes - if the problem goes away, you have a set of all good with one bad tube in your hands, and you have to go back and try each one anyway - you don't want to throw away your expensive NOS rectifier unless you KNOW it has gone bad.

Report back when you've tried all of this.

Good luck!

mikefreitas wrote: I have a new (1 week) Maz 18. The amp sounds amazing when first turned on.
After 10-15 min of playing, the amp slowly loses volume and eventually has a very weak thin sound.
I reseated all the tubes and the problem persists.

Wondering if this is just a bad tube or do I need to send the head back.
Any help appreciated as I was really looking forward to gigging with this amp soon.

*** Update ***
Turns out that the problem with the amp was the FX loop.
Patching a cable across the send/return jacks fixed the issue.

benttop wrote: Get some DeOxit or similar cleaner, and with the amp off, spray it in the jacks.
Then work a plug in there a few dozen times. That should restore it to working without the jumper cable.

This is a common problem by the way - They don't make jacks like they used to apparently...
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