Blew my Mesa?

[hydro]

The Magic Smoke has been released from my Mesa 5:50+. Was playing, noticed sound weaken. Saw one power tube go dark but still tried to keep playing; then after a few minutes on one tube, nothing. I can get very very low output now but nothing else.

The power tube was loose and I reset it, no dice. Tried a different set of power tubes, still nothing. All the pre and power tubes will light up and look fine, fuse good, lights good, I do get some very quiet sound but barely audible especially on the clean channel.

Any ideas? The transformers don't get hot at all; usually they are blazing.

I think what may have happened was that a power tube got knocled loose while I was moving it and then when I was playing, something else fried because of it. Just wondering if anyone has any suggestions. I opened it up and there's nothing obviously blown inside - just really low volume output. The power tubes get hot but they don't ever really start to blaze or react to playing or volume.

Thanks

 

[Chickenwings]

Re: Blew my Mesa?

screen resistors burn out when a tube is not sitting right.
They are the 470ohm ones that go across the top of the tube socket (at least that is where they are on fender amps...dont know about mesas).
They will definitely smoke up and do all the things you have talked about.

 

[Kamanda~SD]

Re: Blew my Mesa?

Saw one power tube go dark but still tried to keep playing; then after a few minutes on one tube, nothing. I can get very very low output now but nothing else.

Do I even need to say it? ...

Bring it to a tech

 

[hydro]

Re: Blew my Mesa?

screen resistors burn out when a tube is not sitting right.
They are the 470ohm ones that go across the top of the tube socket (at least that is where they are on fender amps...dont know about mesas).
They will definitely smoke up and do all the things you have talked about.

Dang it that's what I was afraid of. They have fried on this amp before and I bet they failed again....

My nearest authorized tech is a long drive but I guess I gotta go...

 

[Myaccount876]

Re: Blew my Mesa?

Dang it that's what I was afraid of. They have fried on this amp before and I bet they failed again....

My nearest authorized tech is a long drive but I guess I gotta go...

Sounds like you need to put in higher wattage screen resistors then. Try 5W fireproof resistors. If those burn out, then something else is sending either way too much voltage or way too much current through those resistors.

 

[Vasshu the humanoid typhoon]

Re: Blew my Mesa?

^It is a Mesa...so yes...loads of voltage in all kinds of places

 

[jeremy]

Re: Blew my Mesa?

when you notice something is amiss (such as one tube going dark for example) its usually a good idea to stop playing and power down the amp since something is obviously wrong

 

[Mincer]

Re: Blew my Mesa?

Yeah, I was going to ask why it seemed ok to keep playing. It probably was a tube initially, then things got worse. I don't push my Mesa very hard, so I've never run into this (and hope I don't).

 

[Chickenwings]

Re: Blew my Mesa?

Sounds like you need to put in higher wattage screen resistors then. Try 5W fireproof resistors. If those burn out, then something else is sending either way too much voltage or way too much current through those resistors.

I was gonna say this too.
Actually it is a pretty easy fix. Just replace the toasted resistors with the new beefy ones.
Same ohmage, but higher wattage makes them more reliable.
Of course they will still cook if your tubes are not seated properly but worth doing nonetheless on pretty much any amp.

 

[MetalManiac]

Re: Blew my Mesa?

I was gonna say this too.
Actually it is a pretty easy fix. Just replace the toasted resistors with the new beefy ones.
Same ohmage, but higher wattage makes them more reliable.
Of course they will still cook if your tubes are not seated properly but worth doing nonetheless on pretty much any amp.

Assuming it didn't take out a bunch of other stuff including , the bias supply circuit, or even the the PT. I don't know what kind of fuse circuit Mesa employs.Also, 'Ohmage' isn't a word.

 

[hydro]

Re: Blew my Mesa?

It probably was dumb to keep playing. It was still making sound though!!

I took it to the tech today and hope that it will be sorted soon. I have a good backup rig for my gig Friday so I'm OK.

 

[Chickenwings]

Re: Blew my Mesa?

Have another beer Jerry
http://www.collinsdictionary.com/dictionary/english/ohmage
http://www.merriam-webster.com/dictionary/ohmage
http://www.dictionary.com/browse/ohmage
https://en.wiktionary.org/wiki/ohmage

 

[MetalManiac]

Re: Blew my Mesa?

^ damn, I'm sorry man.

 

[Chickenwings]

Re: Blew my Mesa?

lol its all fun and games.

 

[Myaccount876]

Re: Blew my Mesa?

Assuming it didn't take out a bunch of other stuff including , the bias supply circuit, or even the the PT. I don't know what kind of fuse circuit Mesa employs.Also, 'Ohmage' isn't a word.

Usually if the screen resistor(s) sh!t(s) the bed, it's because it's a bad power tube, and the power section is disconnected from the OT XFMR when the resistor burns up, so there shouldn't be any damage there. If you have a resistor and the power tube is bad, then the OT XFMR is still fine - the tube will die and you won't have to go through the burden of replacing the resistor. The only argument for using the screen resistor as a "fuse" is to protect an already failing power tube from already failing - trying to avoid the inevitable as it's already too late AND now you have to replace a resistor. Use screen resistors with a high enough power rating and replace power tubes that are failing. Done.

 

[hydro]

Re: Blew my Mesa?

Reanimating this thread because I got the amp back today. Well, I went by this guy's shop. Keep in mind he's an authorized Mesa repair tech. He says the amp is working. In his shop he has it hooked up to some pretty small speakers, and he's playing through it and it sounds OK. My family was in the car waiting and I trusted that the rig would be alright, so I left pretty quickly. Got it home and plugged into a *real* cabinet, and it has almost no volume. When I looked at the levels he had set, the masters were cranked - and it was on the dirt channel too; if the amp was working properly they would have heard him a mile away.

I know I am a dumb@ss for not putting the thing through proper paces and checking it out, but I had stuff to do and family waiting. This guy is in a little shack in BFE and I am not going back there again, authorized Mesa or not.

What I can't figure out is this - the amp sounds fine, all the controls work, it's just very very low volume. The transformers don't really get hot; usually they could fry eggs. It's like the power section just isn't doing anything. All the tubes light but there's just nothing going on. With the master volume dimed and set to 50 watt power scale, this thing should be blowing out windows but it's not even as loud as my Princeton set to 2. Have I blown a transformer or something?

It is louder, slightly, than when I took it to him. He said something about transistors in a "mute circuit" that were not working right and that he replaced them. I just can't figure out what might be wrong with it. Both the Mesa authorized techs in my neck of the woods are pretty much useless (the first guy, when I got the amp back it smelled like cat piss for weeks although he did fix it). I have another place to go but I don't wanna pay.

On top of it all he left the preamp tube spring covers off, which I didn't notice until I got home 30 miles away. AAARGH.

The good news is my Sovtek MiG is supposed to land Monday. I just hope to God that Natasha is in one piece when the UPS gorillas are done with her....

 

[Brandenburg]

Re: Blew my Mesa?

^^ well that sucks.. hope you get the amp sorted out

 

[hydro]

Re: Blew my Mesa?

Interesting - on a lark, I tried plugging my guitar straight into the fx return, bypassing the entire preamp stage. Loud. The power section works - fine, from what I can tell.

That's a relief in the sense that it probably means the transformers are OK. Something else must have cooked, or the guy that worked on it may have identified the problem but didn't fix it properly.

 

[dave74]

Re: Blew my Mesa?

My advice would be to just wait until you have some extra cash then pull the tubes, pull the chasis, bubble wrap the hell out of it and send it to the Mesa shop.
Just call and/or email first and talk things over with service before shipping it. Also, make sure to get a box big enough to crazy-wrap it, but not bigger than needed (this will help with the cost).

 

[hydro]

Re: Blew my Mesa?

My advice would be to just wait until you have some extra cash then pull the tubes, pull the chasis, bubble wrap the hell out of it and send it to the Mesa shop.
Just call and/or email first and talk things over with service before shipping it. Also, make sure to get a box big enough to crazy-wrap it, but not bigger than needed (this will help with the cost).

Well it is my main amp. I have backups though and I did consider shipping it to them to get it straightened out. I probably need to call their phone support and get suggestions... mostly I just want it to work again as soon as possible...