Triple Rectifier issue.

[TritonStudios]

Hello, a newbie here at the forums - seems like a nice place after all the threads I've checked out. Looks like there are some very knowledgeable people here.

So. I have a Mesa/Boogie Triple Rectifier. Beautiful amp with great tone - but it has given me nothing but headaches. The most recent started yesterday and I haven't been able to pinpoint the issue other than "Maybe it's a tube thing?"

Here it is:
On channel one, no sound of the guitar comes through, only a loud, bassy rumble.
Channel two did the same thing for a while but seems to have stopped and is fine now.
Channel three is just fine. You know, the high-gain channel that made rectifiers famous and should be the most noisy, but isnt!? Makes total sense.

The 12AX7 tubes all seem to be fine, producing an even level of glow. The 5U4 rectifier tubes seem fine, a little noisy, but fine. The 6L6 power tubes are probably the culprit (if this is indeed a tube issue) because the blue-ish glow they produce tends to faintly flicker with the rumble when I put the amp to channel one and observe the tubes.

I run a recording studio and this amp (the only one we keep in house) could be needed at any time and I'll be screwed if I don't get this sorted out soon! Hopefully someone can help.

[Enzo]

Hi, welcome to the forum.

You are making some assumptions that are incorrect.

First, the glowing heater in each tube. If it is glowing, that tells you one thing and one thing only about the tube - that the heater is running. By the way "heater" and "filament" mean the same thing, so if you encounter the other word... there you go. SO just because the 12AX7s all light up, you cannot assume they are all "fine." A totally dead 12AX7 can still light up its heater.


The 6L6 power tubes are what makes sound come out the speaker. They have no idea which channel you have selected to play through. This would be like saying, my car starts every time for me, but not for my wife. Must be the battery. No, how would the battery know who was turning the key? 6L6s sometimes have the blue glow, normal enough, and current through the tube can affect the glow. ANy sound coming through the power amp will be a changing current - whether noise or music. The tubes amplify whatever comes their way, they have no idea if the sound they amplify is desirable or not. SO all the flickering blue light means is that the tube is amplifying SOMETHING.

SInce the power amp works for channel 3, it must be OK, and you have a preamp problem.


I would take a spare 12AX7 and go down the row of small tubes, substituting the new 12AX7 in place of each of the old in turn. If one of them were bad, replacing it should return the sound. It is also possible there is a problem inside the amp.

The voltages inside this amp can KILL YOU. DOn;t go in there unless you know what you are touching.

The first thing I check inside these Mesas is the controls. If you wiggle the knobs, each control has a little wiggle room in the shaft. ANy that5 wiggle a lot more than the others is suspect. I go down the rows of controls and wiggle the rear covers. If any of the metal covers are loose, that is a problem. That control needs to dismount and have the little tabs crimped tight - the ones that hold the cover in place. The cover not only covers, it is also responsible for keeping the moving contact in position to work.

And beyond that, it will be electronic troubleshooting to locate the fault.

[Chuck H]

I will add that I have seen oxidized sockets cause problems in MB amps often. Try gently wiggling the preamp tubes in their sockets. If this makes noises or changes anything, clean and retension the sockets. If there is no change, try different preamp tubes. If there is no change after that you may have a bad trace on the board where a socket is mounted OR you could have a bad LDR or perhaps it's power supply. In which case I would suggest a tech. But the tubes and sockets being oxidized should be safe enough to manage and may be where the problem is.