Dual Rectifier Trem O Verb switching

[tonezoneonline]

I've got a Dual Rectifier Trem O Verb that when put on the red channel is intermittently switching in and out on it's own.When I say in and out I mean that channel will work and then not work and then work again.These amps are really not my thing so any help would be appreciated.

[Enzo]

Intermittant loss of sound is an entierly different problem from switching channels on its own. Does smacking the amp have any effect? (Looking for loose connections) Does wiggling the tubes make a difference? Use an insulated probe - fancy word for a chopstick or something - push the various components on the boards around to se if anything is loose.

[Amp Kat]

Man I don't know why this problem is so eminent in Mesa's but it seems like every time I turn around this is happening to one. I first thought it was linked to the opto Vactrol's VLTC series because the customer said it definitely isn't doing it any more. Then this customer brought another one in and it's doing it too but it's intermeittent and no opto's but relays and sometimes I can't get it to do it unless I really crank it for all it's worth and my neighbors get a little edgey . It's not just the Dual and Triple recto's either. I've seen it on combo's and the single rectifier heads. Some light would be cool as well and I've scoped it to no absolute cause yet but I'm still plugging away.

[tonezoneonline]

Thanks for your help Enzo and Amp Kat is correct.I thought it was the Vactrol's too but don't see it.This is an old amp of mine that I never use and thought I would have another look at it and decide what I was going to do with it.I'm going from memeory as it's been a few months since I've messed with it.
I'll plug it in tomorrow and be a little more detailed in the description and see if we can figure this out.
Thanks guys

[tonezoneonline]

Plugged the amp back in this morning and yes,it's intermittent.No amount of banging effects it.As I remember the last time I had it out I pulled the board and checked for bad joints or traces.Checked the Vactrols and could not find a problem.I do have a schematic and tried to trace several things but it's been a while.It will play for a few seconds and then loose all sound .After a few seconds in comes back in.Filaments and pilot stay lit.The problem orignated on the red channel .

[Mark Black]

Not that it will be the problem with YOUR particular amp, but I have worked on quite a few Mesa's with intermittent signal problems and most of them have been due to control pot problems. There seems to be two main failure modes:

The knobs stick out just a little too far and are prone to getting whacked, which can push on the shaft, bend out the tabs on the back-shell and make the whole assembly a little loose, allowing poor or intermittent wiper contact, Pulling on the afflicted control will usually make the signal come back, and it's usually either the Volume, Gain or Treble control (or a combination) which is at fault. These can usually be fixed by removing the pot from the chassis (leaving the wires attached) just enough to get to and crimp the back-shell tabs over again.

The other variation I have seen is a problem with the wiper contacts themselves. They are held in place on the rotating plastic part by several melted-over plastic pegs and on some particular brands of pot Mesa have used these melted-over pegs break off, allowing the wiper contact to lose tension as it no longer has a good anchor. I remember I could actually see the abnormal setting of the wiper contacts at full rotation (CW or CCW I don't remember) relative to the way an identical brand pot at another location looked. The models I experienced this problem with all had at least two different brand/style pots mixed in various locations, but again the trouble-maker was usually Volume, Gain, or Treble. I have successfully repaired these, but that's just a sickness I have they really should be replaced.

Oh yeah and rarely I have found a pot wire broken at the PCB but still touching - pretty easy to ferret those out...

Anyway I only hope this is some help, and good luck!

Mark

[Enzo]

THat is certainly true. On the newer Mesa with the 16mm pots, whack the knobs and it pushes the back of the pot out. Grasp each pot rear cover and see if it is loose. If so, remove the pot so you can squeeze the little tabs back down to retighten the structure. I have had to fix any number of those. I had forgotten about it.

[Amp Kat]

I've also seen this on Crate combos where it was the treble pot causing the channels to switch bythemselves and turning the pot would do it every time. I'll have to check that Mesa and see.

[Enzo]

My experience with Crates switching channels by themselves was that the FS jack cutout contacts were dirty, so the T and R contacts would not be well grounded. SOmething else to check for.

[Amp Kat]

Hey thanks Enzo because unfortunately, I have another Crate in that is doing that also.

[Amptek]

Ask Mesa for the schematic diagram. Replace the VACTROL number 11.

ciao !

Mike

[Enzo]

Whenever I get any amp in with the CLiff type jacks, I always check the resistance of the cutout contacts. They need to measure less than half an ohm. If it measures 2 or 3 ohms or 14 or whatever, it will work, but that higher resistance means the contacts are dirty, and they will at times NOT work. I burnish them with my trusty GC9337.