Troubleshooting my Mesa Tremoverb

Doug Notter

Doug Notter

Inspired
Think I have a bad tube but not sure if that's what would cause this problem. Also not in the video is, if you're playing on the high gain setting, as you turn up the reverb a clean channel starts bleeding through and mixing with the high gain sound. I've never run into this before so just hoping someone else has and can save me some grief. Tubes are obviously expensive right now so not trying to replace them all. Just want it working right so I can sell it honestly. It's been sitting for about six years. I'm feeling guilty. It's like a bird in a cage. lol

 
Since its been sitting, I'd start by spraying electrical contact cleaner on the tube pins, then working them into the connector. You could have some corrosion built up causing a pin not to make good contact. There's also some basic tube troubleshooting instructions in the Mesa manuals.
 
You might try pulling V5 and V1 individually and seeing if either one affects it. After watching the video, it sounds like some kind of oscillation going on in the circuit, and pulling each tube might help track down where it is.

On another note, I LOVE Tremoverbs. They're tied with the Road King as my favorite in the Recto series. If I could afford it, I'd buy it off of you in a heartbeat.
 
that oscillation could be a microphonic tube, if V1 is indeed part of the reverb circuit as well, I would sub in a good 12ax7 and see if it changes. That spax7 is just a low noise 12ax7 with shrink tubing on it.

The clean channel blending thing may be an LDR issue? I know some tremoverbs had iffy LDR’s in the channel switching.

Tannhauser said:
Could that potentially damage the amp? I have a valve combo with (I assume) a bad valve that I've been too scared to tinker with!
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You won’t damage the amp by running it with a preamp tube pulled, but if you pull it or insert it when the amp is on you may get a loud pop depending where it is in the circuit.

Likely also will get no sound with a preamp tube pulled, again depending where it is in the circuit.

Running the amp without power tubes installed potentially could damage things, dependent on amp design - power tubes draw a lot of current even at idle, and with them out = less current drawn from the power transformer = B+ will be higher, potentially higher than the ratings of filter caps and other caps, but if the amp was spec’d with high enough voltage caps then no problem.
 
Doug Notter said:
LDR? Not sure what that means.

I appreciate everybody's input. Hopefully I can get it squared away without a trip to the tech.
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Light dependent resistor, or photoresistor, Mesa used to use them in channel switching and I remember hearing they got a bad batch at one point back in the 90’s. Other than that, they can go bad with age. Most manufacturers have switched to relays for channel switching at this point.

The mention of the bleeding clean channel made me think of them but only a tech would know for sure.
 
This thread smells like future regret. :)

I would not sell it. I have the same amp.

Some good advice tossed out there. You don't need anything other than
a standard 12AX7 in V1 to test it. Not gonna hurt it by pulling preamp
tubes--as someone else already stated.
 
la szum said:
This thread smells like future regret. :)
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I've been keeping it for years and I just don't use it at all. The Rectos have never even been my favorite. I prefer the Mark series but really ever since I got my AxeFX3 I'm just not even interested in these things anymore. Nostalgia is the only reason for me to keep it at this point and the only reason I've been keeping it the last few years. Who knows though. Maybe after I fix it I'll decide I can't part with it yet.
 
Have you at least tried cleaning the tube sockets yet? That should always be the first thing to do when suspecting trouble, especially if the amp hasn't been used in a long time. Simplest things first. Unless it's something like scratchy pots. Which, in that case, they should be cleaned. ;)
 
TSJMajesty said:
Have you at least tried cleaning the tube sockets yet? That should always be the first thing to do when suspecting trouble, especially if the amp hasn't been used in a long time. Simplest things first. Unless it's something like scratchy pots. Which, in that case, they should be cleaned. ;)
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I haven't done anything else with it just yet. Just making a list of things to try when I get back to it. When I replaced the one tube I did just give them all a wiggle to make sure they were seated well. I live in Phoenix and things don't really corrode here the same way they do in other places. There's no corrosion on the tube I pulled at all that I can see but I've got some contact cleaner I can hit them with next time. A couple of the pots get scratchy (master volume mostly) when it sits but just working them back and forth a bit has always cleared it up and it doesn't return until it sits a while again. Other than whatever is causing this problem the amp is actually in great shape. Minimal scuffing on the bottom corners. Screen is perfect. It's had an easy life. I think it may just be getting bored to death. :D

There's an authorized service center not far from me if it comes down to that. It sucks to spend money on something just to sell it but I'd do that before I sell something I know has an issue. I'm not qualified to do much more than swap a tube so it's probably going to the shop honestly. I don't see how a tube could cause the channel blending issue when you turn the reverb up. Someone on Facebook even suggested the reverb tank can become microphonic which is new one to me. Never even heard of that.
 
Doug Notter said:
It sucks to spend money on something just to sell it
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Yeah, it does. But with it having a problem, you'd get nothing but lowball offers. People would have no idea the cost of repairs, so it's kinda to be expected.
Doug Notter said:
I don't see how a tube could cause the channel blending issue when you turn the reverb up.
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Ya never know. My Dual Rec had a problem with one channel dropping out, and cleaning and working those pins in and out fixed it. I actually learned about doing that on an internet site that sells tubes. They must've had that tip in 3 different places on their site, and even posted an email response from someone who was amazed that that had fixed their issue. Iirc, they said tubes not making good contact were responsible for some high percentage of easily-fixed-by-the-owner, issues.

Another thing I just thought of..., take a close look at your tubes when you pull them, and look to see if any have cracks in the glass. And I would definitely grab the Mesa manual, because it has 2 pages on how to check your tubes.
 
I'll definitely be giving it a shot before going to the shop. If I can fix at least one of the problems that should net me a smaller repair bill if nothing else because I'm not sure if the channel blending and noise/feedback issue are even related at this point.

Has anyone ever heard of a microphonic reverb tank before? I've never taken one apart but I can't even guess how that would or could happen. What's in there that can cause it? If that's even a real thing.
 
Doug Notter said:
Has anyone ever heard of a microphonic reverb tank before?
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Any time the word 'microphonic' is thrown around, I think of tubes.
I just looked in the manual, and V5 and V1 have reverb functions. V4 is the effects send & return, so maybe try swapping V4 with V5 and then V1...?
If you don't already have it, the manual is available at the Mesa site, so you can see which tubes are which (if you don't have it handy.)
 
They actually have the tube diagram on the inside of the cabinet. I just need the manuals for the troubleshooting section.tremoverb.png
 
I got to thinking about it today. One half of V1 is the very first gain stage in the amp (that's why they spec a low noise tube there) and the other half is part of the reverb circuit. That might be where the channel bleed is coming from as well as the oscillation. I would definitely target that one. Like others have said, pulling a preamp tube won't hurt the amp, or you could sub a 12AX7 there with no issue.
 
^Yup. And since V1 does most of the heavy lifting it tends to go bad well before any
of the other preamp tubes.

Can easily troubleshoot it by swapping V3 or V4 for V1 and see if it helps.
 
Took me a minute to get back to this but here's a small update.

Replacing V1 with the 12ax7 I took out of V5 made the microphonic noise go away. However the channel bleed and hum when the reverb is turned up remained.

I just unplugged the reverb tank expecting the reverb control to have no effect at all but it actually still does. Turning it up turns the sound to crap and the channel bleed is still there when you turn it up. Not present at all when reverb is set to 0 just like when it's plugged in. I noticed Stew Mac sells replacement reverb tanks but having the same problem with the tank unplugged has me thinking the tank itself isn't the problem.

Can a power tube or a rectifier tube cause this kind of weirdness? I didn't notice anything relevant in the manual that would indicate a problem with one of those but I really have no idea at this point. I hate to take it to a tech just to find out it was a tube but I don't have any spares to test with either.

Me and my back really don't like this thing very much right now.
 
You'll need a known good 12AX7 in the V1 and the V5. V5 is Reverb Driver (V5A) and Mixer (V5B). V1B is your
Reverb Return. So both of those tubes need to be in the amp and known to be non-microphonic and functioning
properly.
 
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