Single Rectifier with burn marks, need help! Pics inside

[DEz10DEz]

Hi!
Some time ago, my amp, a Mesa Boogie Single Rectifier Solo 50, began to have a slight loss of sound, the volume decreased to a very low and sterile sound and it ended up disappearing. I would put the amp in standby, turned the switch on again and everything was back to normal. This was becoming more constant until the fuse blow. I realized after that, as I suspected, it had a bad power tube. I changed the two tubes and everything went back to normal for a while . Then problem stated again, the sound fails and with an increasingly regularity and I´m constantly switching the standby on/off to keep playing.. Yesterday I went to exchange the preamp tubes to see if the problem could come from there, and I remembered take off the chassis and take a peek inside. I found this:

The contacts of the resistors seem burned and these are right between the two power tubes
What might had happened, what could have caused this?
Perhaps because I insisted to play the amp with a dying tube..?
Has anyone had a similar problem ?
Thank you, and sorry if my english isn't the best.

 

[domct203]

Welcome to the forum.

Those look like (what used to be) your screen grid resistors, and they need to be replaced. Don't play the amp.

This was most likely caused by a power tube failure (I suspect an internal arc/short) and was made worse by continuing to play the amp that way. What you described is typical of an intermittent power tube issue and should have been addressed right away.

I recommend the amp be checked by a tech, there could be damage to the PCB as well.

Sorry to see this,
Dom

 

[bandit2013]

That does not look good. Usually when the PCB material over heats, it will delaminate along with copper foil being compromised as well. The close up shot actually appears to be charred flux residue. On the bottom of the picture, those solder joints look like they reflowed.

Dom is right, have it checked out by a certified Tech.

 

[bendo]

That is typical screen grid resistor failure due to power tube failure. Replacing the resistors should resolve the issue. For parts like that, I usually contact Mesa Customer Service and order replacements from them. That way I can assure myself the parts are of the right spec. The PCB should be fine. But, if it's not after replacing the resistors, a good tech can get it worked out. And, I am pretty sure that PCB board is still available from Mesa as a replacement part.

The Moral of this story is "Do not wait to replace the tubes at the first sign of failure." If you had replaced the tubes at the first sign of power loss/fizz/static, you could've avoided would can be a very costly repair.

 

[DEz10DEz]

Hi guys. Thanks everyone for your help. I'm now sure that using the amp with the dying tubes caused this, I should of changed them erlier.. I'm trying to find someone capable of fixing it. Thanks again, and hopefully someone can learn from my mistake.

 

[deeman]

I'm sorry to hear about your amp but let this be a lesson to others out there and perhaps this will prevent damage in the future for many others. I'd like to know what the tech finds out and what the total damage was.