Mesa/Boogie Dual Rectifier problems after power surge

[AGrayson84]

Hi everyone. I picked up a new Mesa/Boogie Dual Rectifier (3-channel) back around 2000 or 2001 when I was still in high school. It was such an expensive item to me that I bought a surge protector to carry around with it, and used it every time I plugged the head in... .....except one day when I left the surge protector at home on accident and was jamming with some friends. Low and behold, just as my luck would have it, that very day we had a power surge while playing. At the moment of the surge, the head lost power (of course), and when the power returned a second or so later I recall something distinct happening with the head... but that day in 2001 was too long ago for me to remember if it was just a sound that the head made when power came back, or if smoke actually creeped out of the back of the unit. The glass fuse had blown, so a week later I do recall that upon powering the device up and looking at the back of the unit after the surge, only 3 tubes were working. I think they were the last 3 tubes from the far-right (the smaller-sized tubes). I believe the 2 larger tubes, and the small tube immediately next to the large tubes were blown from my memory.

A couple weeks later I ordered some new tubes, hoping just the tubes went bad. Every time I put the correct new tubes in place of the blown tubes, the new tubes would blow as soon as I kicked the power on. I don't recall if the tubes would blow after simply powering the unit it on, or if it happened after taking it off standby (I want to say the latter), and don't recall if the glass fuse blew each time the tubes blew... but I think it did. I refused the thought of taking the head to a licensed repair shop and probably pay $500 or more just to have it repaired, so I continued running it on just the 3 far-right tubes since I was still able to use one of the gain channels like that without issue.

13 years later, the head is still otherwise in mint condition due to the very little use it has had, and I'd like to possibly try tackling repairing it myself. I don't have a major in electronic repair, but with some guidance I'm sure I can repair/replace whatever is needed, provided the part is not impossible to replace due to be discontinued or something. I have found several wiring diagrams for Dual Rectifiers on the Internet, but the diagrams vary for the different models of this head that have been released over the years. How do I know which diagram I need, exactly? Any ideas where to start looking for the problem, based on the issue that I have described? Thanks in advance!!!!

Best Regards,
Andrew

[drewl]

So you're saying you used the amp for 13 years with it only pushing one side if the output transformer?
Didn't that sound really bad?

Are you sure it wasn't the two rectifier tubes that went bad?

What do you mean when you said the replacement tubes "blew" they probably just aren't conducting unless one half of the output transformer went bad.

Did it blow any fuses at the surge?

Any signs of burnt components or wiring?

[AGrayson84]

Thanks for the response! Yeah, that would be a true statement, assuming only one side of the output transformer was working-- that part I wouldn't know how to confirm. I only used it a handful of times like that for the past 13 years, haven't really played through it much at all since this all happened. It honestly sounded just fine on channel 3 in "Modern" mode. Stage 2 and "vintage" mode had problems.

I recall the larger (rectifier?) tubes AND the smaller (6L6?) tube immediately next to the larger tubes blowing. I could tell they were blow because with a new fuse and new tubes they would burn out when you kicked the unit on. You could watch them blow from the back of the head, and replacing the fuse again did not allow the tubes to kick on at all. They were definitely blown at the time of the original incident, and again when I tried replacing them with new ones.

If I recall correctly, I'm pretty sure the glass fuse (I remember it was a "SLO BLOW" fuse) blew initially, and each time I tried a new fuse with new tubes, the new fuse would blow along with the tubes.

Unfortunately I never got around to disassembling it over the years to look for any signs of anything burnt. No burnt smell when I have used it, nor signs of ill effects when I have used it after the incident.

The head stays at a summer house my folks have 2.5 hours from me, so maybe next time I go down there I'll tear it apart and take pictures of what I find.

[52 Bill]

I recall the larger (rectifier?) tubes AND the smaller (6L6?) tube immediately next to the larger tubes blowing. I could tell they were blow because with a new fuse and new tubes they would burn out when you kicked the unit on. You could watch them blow from the back of the head, and replacing the fuse again did not allow the tubes to kick on at all. They were definitely blown at the time of the original incident, and again when I tried replacing them with new ones.

I only used it a handful of times like that for the past 13 years, haven't really played through it much at all since this all happened. It honestly sounded just fine on channel 3 in "Modern" mode. Stage 2 and "vintage" mode had problems.

So the amp still worked with the blown tubes/fuses?

It's unfortunate that as a high school kid no one was willing to advise you on how to deal with this situation and you let it go for 12-13 years. I would imagine that you could have used the amp a lot more and enjoyed it if it was working correctly. It did come with a warrantee and I doubt that a repair shop would have charged you that much money back then to fix the problem.

In any case, you need to have the amp in front of you and you need to tell us specific things so that we may be able to help you through the repair process. As it is, your description is confusing and will lead to frustration on your part as well as ours.

[AGrayson84]

So the amp still worked with the blown tubes/fuses?

It's unfortunate that as a high school kid no one was willing to advise you on how to deal with this situation and you let it go for 12-13 years. I would imagine that you could have used the amp a lot more and enjoyed it if it was working correctly. It did come with a warrantee and I doubt that a repair shop would have charged you that much money back then to fix the problem.

In any case, you need to have the amp in front of you and you need to tell us specific things so that we may be able to help you through the repair process. As it is, your description is confusing and will lead to frustration on your part as well as ours.

Yep, the 3 smaller tubes still kept it running and sounding just fine on channel 3. Excuse my ignorance on the tubes, it's been a while since I've known the difference between the two types of tubes in the unit.

Yeah that long ago the only option was to really take it to a certified shop, there were no diagrams on the Internet-- I looked haha. I assumed, based on how expensive the head was in the first place, that repairs on it would be costly. I only called the 2 closest Mesa-certified repair places near me (at the time they both were 2+ hours away), and they both wanted $250 just to tear it down and determine the problem. So I figured with parts it wasn't going to be cheap, and I pretty much only used channel 3 so I kept using it with the 3 blown tubes. And unfortunately, as far as the warranty goes, Mesa/Boogie told me that the warranty doesn't cover repairs due to fried components from power surges... so I never attempted to pursue sending it back to them.

Good enough though... I will bring the amp back with me next time I go to Virginia and help you guys help me to figure it out. Thanks guys!

[The Dude]

It would also be helpful to know what you mean by "blown tubes"; filaments not lighting, shattered glass, checked bad on a tester, etc.

[AGrayson84]

Sorry THE DUDE, I had typed a response to you but looks like I may have hit the reply button after. The filaments are what's blown. The glass fuse and the same 3 tubes blew twice in a row after replacing them with new ones and simply replacing the fuse will not allow the tubes to power up for a split second since they are already blown. There's a black discoloration in the glass of the tube each time a new tube blows, similar to a clear light bulb. I'll watch the 3 new tubes power up for a split second, then they blow right now.