Mesa Triple rectifier blown output transformer?

[NEVIEM]

Hi guys!
I`m in a big trouble with my amp, hope somebody can help me around here, or point me at right direction.
I own a Mesa Triple recto 3 channel (it should be 2009 model) I got it used from U.S. and use it with external 500 watt power exchanger (or how it`s called in english) so I can run it here in Europe. Few weeks ago while we did soundcheck on one gig it suddenly stopped working. I turned around to see that the amp is turned off. I checked the amp immediately if there`s a smell of burning, but everything seemed fine....tubes didn`t show a sign of damage, and there was no burning smell around the amp, no smoke, anything. So I thought that the fuse just blew, since this hapened few times on my last amp, Peavey JSX, swapping the fuse solved the problem everytime. After I got replacement fuses for amp I swapped it, turned the amp on and heard just a small click in the place where the fuse is. The amp didn`t even turned on, it just blew the fuse instantly as I hit the power switch. I checked everything, tried another fuse....amp did the same thing again. So I took it to an amp tech that I got good references about (not mesa tech since there is no such guy in my country) to check it. First he said that there is probably some short in the amp, after a week I called him and he said that he was not able to repair the amp and he thinks that the output transformer might be broken. He also told me that he`s going to give some contacts on guys that will know what to do further.
How the hell did I managed to fry the output transformer?! This is my third tube amp. Owned a Peavey JSX, sold it because I wanted a mesa, than I have a Bugera 6260. I know how to use a tube amp and I also know that it takes a lot to fry output transformer. I know that one of possibilities is ohm mismatch...I only used amp with 2 x 8-ohm mono cabinets (plugged with 2 cables into 4 ohm output jacks in the back of mesa) and the day the amp blew up I was running through one 8-ohm cab, so I am pretty sure I did nothing wrong.
When I emailed mesa, they said they`re almost 100% sure it`s a bad power tube.
Could somebody help me? Is it really possible I fried the output transformer, or could it be that it is something less serious? Because to me it just seems senseless that amp that`s known for being one of the most reliable, farts out sooner than Bugera.
Also one of my friends has a good experence with electrical devices and said he could find the problem but needs schematics for amp, because without it, it will last him really really long to find the problem. Is it possible to achieve schematics from mesa?
Thanks in advance guys, hope somebody could tell me what the hell is going on.

 

[94Tremoverb]

If the fuse blew as soon as you turned the power on (not the standby, if it was in the standby-on/mute position) the problem is the Power Transformer, not the Output Transformer. Or, it could be the rectifier - tube or solid-state - but if your tech said the transformer, assume that it is (at least for now).

What is your 'power exchanger' like - is it a large, heavy object weighing at least a couple of kilos? If so, it's also a transformer (called a "step-down") and is the right thing to use, although 500W is at the lower end of the range you need for this amp. Or is it a small object that weighs a fraction of a kilo? If so, it's a solid-state "voltage converter" and is not suitable to run a guitar amp, and could have caused the damage.

If is is the transformer that's blown, the only solution is to replace it, which in Europe is not going to be cheap. If you do, at least you should be able to get a Euro voltage type though, so you won't have to worry about stepping down the voltage any more. But hopefully it's something else your tech has missed, like a shorted rectifier diode (remembering that this amp has both tube and solid state, so pulling the tube rectifier does not eliminate it as a possible cause!).

 

[NEVIEM]

Yes, the fuse blew immediatly as I turned the power on, I didn`t even have a chance to touch the standby switch.
Exactly the step down transformer is a correct word.


Uploaded with ImageShack.us Guys on our local forum recommended me this transformer, and I also found it on some german music store site and it had good for mesa triple recitifier etc written in description. It weighs around 2 kilos.
How much could it cost to change a power transformer?

 

[94Tremoverb]

It could cost two or three hundred Euros .

That unit *looks* like it's OK, but it also doesn't look all that high quality - I know, it's hard to tell from a pic but I've seen several similar unit that are at best 'acceptable', rather than really good... has your tech checked that it is giving out the correct voltage? There is one particular type of failure with an external step-down transformer that could result in the amp receiving nearly the full wall voltage instead of the correct 120V. (A failure at the neutral connection of the winding, if you want to pass that to your tech).

It's also possible that too much voltage on the input would blow a rectifier diode and not the transformer, so make sure your tech is right before spending any money on a new one! Replacing a diode is a €10 job (well, maybe a little more including time to investigate, minimum charge etc - but not anything like changing a transformer!).

The very first thing to test is that it's not a tube filament short - which is still just possible. Remove all the tubes, and turn the amp on - just the power. If it now blows the fuse it's the power transformer, the solid-state rectifier diodes or a shorted filter cap, there's really nothing else that could do that. Don't turn the standby off (play) with no tubes in.

 

[espboogie123]

Yup, remove all the rectifier tubes and power tubes. Replace fuse and see if it stays on. If not, a tech needs to take a look at it.

 

[NEVIEM]

Thank you guys.
These are awesome suggestions. Im going to ask everything you mentioned.

 

[playdosboogies]

Even though that step-down tranny looks a little cheap, i'm still willing to bet it all started with a failed tube.

 

[94Tremoverb]

Even though that step-down tranny looks a little cheap, i'm still willing to bet it all started with a failed tube.

In that case I'll bet against you (assuming it *is* a blown PT and not a shorted diode) .

It is possible, but in all the time I've been repairing amps, I've never seen a Mesa with a blown transformer (either one) caused by a failed tube.

But I *have* seen a Mesa PT fried here in Europe by using the wrong type of step-down unit - admittedly one of those solid-state 'voltage converters', not a step-down transformer - so my bet would be on that or some other supply problem.

The big problem with auto-transformers (which it almost certainly is, like most step-downs) is that a failure at the neutral end of the coil leaves the output connected directly to the input with only the inductance of the top part of the coil in between... so almost the full voltage gets through - not good.

I'm still hoping it's a diode though. For a tech not familiar with a Rectifier, it would be easy to pull the rectifier tubes and think that because it's still blowing fuses it must be the PT. I almost made that mistake with a Blue Angel until I realised that it does have two separate rectifiers, one of which is solid state.

 

[NEVIEM]

The problem was solved yesterday. Thanks guys!!!
I went to my tech and asked him what is the problem and how could it happen. He said it might be the tranny and that it is possible that someone connected the amp straight into power without the step down transformer...seemed pretty strange to me, as the amp blew while I was playing it.
Then I looked to the back of amp to find that probably nothing has been touched, and also my old fuse I put there was still in and not damaged. I didnt want to do anything dumb so I waited for my friend that has some experience with this kind of stuff.
So first the step down transformer is totally ok. He was trying to measure if the voltage from transformer is ok and everything seemed fine.
So the last steps were to determine if my tech even tried to look at the amp or if he was right and there is some more serious damage to the recto. And guess what even though he said that he did try the tubes and they are okay he didnt even bother to touch that amp and lied to me.
We pulled all the tubes out and BAM! the amp was working (just turned the power switch on not the standby...I noted this in case somebody in the future will experience same problem). Next step was to try if its some power tube or rectifier tube....we put all the power tubes in, switched mesa to silicone diode rectifying and turned it on. again the amp was working. So my problem was bad rectifier tube.
Thank you very much for the great suggestion about getting all tubes out and try to turn the amp on (I didnt know that its a good idea t. I really much apprecciate it. I dont even want imagine when would I get my mesa in working condition if I relied on tech. He wanted to send me to some other guy to look at it and I bet that would last another few weeks.
Thanks again!!! All best to you!

 

[UnderJollyRoger]

Well, glad it's ok now.

So, in conclusion: never trust anyone

 

[94Tremoverb]

:shock:

It never even occured to me that a tech could miss a shorted rectifier *tube*. That's the absolute first thing you always check, always, on a tube rectifier amp that's blowing power fuses.

Great news! Important message for the future too: Mesa power transformers are very tough and hard to kill .

Even though that step-down tranny looks a little cheap, i'm still willing to bet it all started with a failed tube.

You win! Although we were both partly right .

 

[iceman]

I love it when a plan comes together. Boogie just posted similar advice..


http://mesaboogie.com/news/2010/11/mesa-amplifier-tube-troubleshooting/#more-1885

 

[NEVIEM]

Hey guys.
Looks like it wasn`t just a blown rectifier tube...I replaced all rectifier tubes, got the amp working, but when I turned the standby switch on one of power tubes was glowing with blue color!
I shut down the amp and ordered a pair of new power tubes. Got them installed, turned on the amp, pushed the standby switch to on position and now all of my power tubes are glowing blue!!! Some are brighter some are darker but every single one is now blue, even the new tubes.
I shut down the amp again...I don`t want to damage anything.
Do you know what could cause this? Could the blown tube take something with it? Like some resistor or anything?
I`m a bit confused, since my amp`s power tubes were always glowing orange before.

 

[iceman]

All my power tubes glow blue, pretty sure that is normal.

 

[94Tremoverb]

Biggest tube myth there is: blue glow is a sign of a bad tube.

*Some* (rare) types of blue glow can be a sign of a bad tube. *Most* types are a sign of a good tube working properly.

I hate to think how many perfectly good tubes (including many of the best and most desirable NOS types, which often do it) have been needlessly thrown in the trash because of this.

Blue glow that appears slightly purple or royal blue on the inside of the glass is good. A small amount of blue glow that can be slightly greenish inside the plates is also good. Bright, neon-tube-like pinkish-purple blue glow throughout the tube is bad, though. Do a Google Image search on 'blue tube glow' to see some good examples.

 

[NEVIEM]

Thanks a lot guys!
I tried the amp really loudly today, and everything is ok
Tubes glow only slightly blue in diode rectifier mode.
My problem was that I managed to swap the wrong tubes, so the bad ones stayed in.
I tried to turn it on and one of tubes was glowing blue much stronger than others and after a while started redplating, I pulled out the pair and put the ones I thoght were wrong back and all is perfectly fine now.
Thank you for helping me!!!