Mesa DC 10 low output

[vetterdog]

I've been having some trouble with my trusty DC-10. I should state that I am not an electronics person. I have a basic grasp of how things work, and I can fix/replace anything on a guitar, but amps are pretty much a sealed book to me. Previously, the amp would take a while to warm up, maybe 4 songs into a set it would just take off, volume-wise, and really get loud and I'd have to turn it down. (I would of course have had it on standby for 10-20 minutes or so before starting) I recently had the output tubes replaced at the shop where I usually take it, (I blew one or two)and they put Groove tubes in it, plus one preamp tube. I previously had Mesa matched tubes (chinese I think)in there, and the amp was always nice and loud, full sounding. Now it has no real volume, and even after a while it never gets to a decent volume level. I am wondering if this would be due to the new tubes or if there is some other undelying issue I should be looking at. The shop that I use I have used for years, they are reputable and knowledgable, but it sure seems like a different amp since I got it back. Gain and everything else seems to be OK, just no balls. Any info will be greatly appreciated. Thanks, Dave

[Mark Black]

Sounds like the amp had some version of this problem before the tube change - they shouldn't radically change volume on their own especially after a 10-20 minute warm-up on standby.

One possibility (among the many) is your amp may have some bad control pots in it. I say this because Mesa had a bad run of them from their supplier so for a few years manufacturing these pots got sprinkled about in various places in various amps. What happens is the "wiper" contact becomes loose or completely falls off the actuator plastic piece inside, leading to intermittent or unpredictable operation. These pots should be replaced if that is the case, along with any others made by the same manufacturer even if they are still working.

Another malady not caused by defective pots but with the same effective results is caused by the control knobs "taking a hit", either by something falling against the knobs, the amp falling over on its face or even sometimes being gently set that way while working on it. The pressure can pop the pot back loose, allowing decreased wiper pressure on the resistance track. These pots can usually be repaired by re-crimping the pot back tightly to the phenolic & bushing plate.

Many times (but not always) both of the above scenarios can be detected by pulling out on a control knob (without turning it) while listening for volume or tone changes.

But yes - tubes can be at fault as well (even if new), either by way of being defective or by simply having a very different gain characteristic.

And then there are certainly other possibilities...

Have you voiced your concerns to the shop? I myself would want to know about it if an amp I had worked on wasn't operating correctly afterward, and I'm pretty sure they would feel the same

Good luck!