one channel on amp not working

I am not an amp tech, but my guess is one of your preamp tubes (the smaller ones) is bad or possibly loose in it's socket. Tubes can work themselves loose over time from vibration and also being bumped around while being transported.

First, turn off the amp and unplug it. :D

If you can see the tubes, carefully pull them out paying great attention to how the pins line up with the socket. Sometimes the pins get a little build-up on them, you can just push them in and out of the socket a few times to clean them up. Make sure they are snug.

Be careful though, capacitors can hold a charge long after an amp is unplugged. You can still get shocked. If you cannot easily reach the tubes (sometimes you have to take the back of the amp off) without touching other components, then take it to a tech. Amps can be replaced, you can't. :D

It's possible for a tube to be lit but not working. Also, the 12AX7 preamp tubes in your amp are each two valves in one. It's possible for one half of the tube to stop working while the other is still okay.

Re. your car and driving around, as we say in theatre lighting, "Excessive vibration is the most common cause of lamp failure" - and a tube is in some ways just a really elaborate light bulb, so.... But you gotta' get to rehearsal, what you gonna' do. Well, try not to put it right over the axle and avoid speed bumps. :wink:

Looking at the flowchart and schematic for your amp that I pulled down from Traynor's site, at a glance (*and assuming I'm reading your info and the diagrams right*) ... Guessing that it's a bad tube, if you swapped V1 and V2 (Preamp tubes 1 & 2) the problem should either migrate to the Lead channel, or cause you to lose both channels. There are three 12AX7's in there, two are preamp valves, the third is a splitter. You'd need to look at a manual and identify which two were the preamp tubes and swap them to do this test.

There's conflicting info as to which tubes do which thing on the drawings I downloaded, the flow chart says one thing and the schemo says another re. which sides of which tubes do which things, so I can't guess which valve would be bad if the problem migrated vs. losing both channels. If this test shows that you have a bad tube you'll have to A/B test each of the two preamp tubes with a new good tube to identify which one is the culprit.

Happy hunting!

thanks, guys.

this is so weird, though. next practice, they were both working again! it's been about 2 weeks and everything's been fine... until TODAY–and we have a big show (for us) THIS FRIDAY. it was working for about a half hour tonight and then the volume started cutting in and out–like bad reception on a mobile phone. i tried the other channel and the same thing happened. i plugged and unplugged, checked pedals and cables, etc., even tried a different guitar... and nothing worked. once the tubes heated up again after turning it off, it started making a popping sound through the speaker. when i adjusted the volume, it got louder and softer with the volume knob.

tomorrow i'm going to track down some new tubes, a back-up amp... but if anyone's encountered anything like this before and can shed a little light, i would be most grateful! i hope it's just a tube issue and not electrical or the speaker... because i have to ship the whole thing back to canada to get it fixed and that's time consuming and a hassle :-/

gah.

I still think it's one of your preamp tubes.

Here is an article from Mesa Boogie, your problem sounds similar to those described in "Diagnosing Pre-Amp Tube Problems".

http://www.mesaboogie.com/US/Dealers/FAQs/faqs.html

I would replace your Pre-Amp tubes and maybe even buy some spares. They are not that expensive. Call your local music store, they may carry the very ones you need.

Yeah, what Wes said. Could be something besides a tube but a tube going south is the most likely thing and until that's ruled out nothing else is worth checking.