Just dropped off a sick Mesa

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My DC-3 is redplating tubes. Tried different tubes but the problem keeps coming back. It seems to be the 2nd socket.

It's with a Dallas shop that everybody says is *the* place for amp repair.

This is the sort of thing that makes me want to buy a JC-120 or Cube and be done with it. I like playing, not fixing and maintaining. :mad:
 
Probably a simple fix. Could be a screen resistor that burned when the first tube went. I'm sure it will be fixed and back in action.

I so hear ya though, I love tube amps, but they are a pain to maintain. I wish I could get the tones I like from a solid state amp.
 
mongooz said:
i thought the plates in tubes were SUPPOSED to glow red:confused:
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:grin:

In this case, the current goes out of control and the entire tube glows bright orange. The amp stops producing any usable volume.

From what I've read, it's usually a component failure and isn't too hard to fix. I'm keeping my fingers crossed.

Unfortunately, it's not an uncommon issue. It's just part of the headache of relying on tube amps.

My Cube Street sounds really good tonight. :P
 
USian Pie said:
This is the sort of thing that makes me want to buy a JC-120 or Cube and be done with it. I like playing, not fixing and maintaining. :mad:
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This kinda makes me laugh. I have no idea how many amps I have owned over the years and I have never had any issues with a tube amp (knock on wood) and I have had at least 3 solid state amps take a dump on me and 2 of them were less than a month old. I hope your amp is a quick and painless repair.
 
Modern Saint said:
Amp mojo
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:grin: thanks. It will be fine, I'm sure.

It's funny - my wife wanted me to go Christmas shopping and pick something for myself. I spent a few minutes with a new cube 80. She liked the sound of it and I liked that it would give me an always-working backup. $400 just seemed like a lot for something that would be mostly a backup amp. It might make sense if I can snag one used.

I also tried a vox night train 15 head. I liked the sound but my other amps do the same thing louder.

Ended up with a voodoo labs pedal power thingy and a korg pitch black tuner. Neither is as sexy as a new amp but both are practical and fill real needs.
 
USian Pie said:
Ended up with a voodoo labs pedal power thingy and a korg pitch black tuner. Neither is as sexy as a new amp but both are practical and fill real needs.
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Very cool of your wife to say that and yes much needed things are more valuable in the long run. You will know when you find the right amp whether backup or one that will be moved to the frontline or share. I believe that amps like guitars bond with players.
 
Got it back today. Here's what was done according to the invoice:

Removed chassis and all tubes. Checked all tubes. Replaced the power tube set and one preamp tube.

Resoldered power tube sockets and screen resistors.

Resoldered reverb tank and cleaned plugs.

Notes also indicate the bias is high but it works in a special configuration with the phase inverter cathode so they left it alone. I don't know about the phase inverter but I read up on this model before taking it in and several sites confirm it is biased way hot. The notes indicate the new power tubes have a lower plate draw.

The new power tubes are Sovteks. The new preamp tube is a Tungsol. It looks like they replaced a Groove Tube preamp tube that was in there before. Honestly, I was a little suspicious of that tube anyway but there were too many other issues to narrow it down as a problem.

Got it home and spent some time playing it tonight. All I can say is it sounds like a happy, healthy amp. The background noise is gone and it seems to run cooler.

It's funny -- the guy said the power tubes in it were old but they were brand new Mesas I bought a month ago. He said one pair was drawing way more than the other. Maybe they were bad tubes from the factory. Maybe a bad solder joint crapped them out with a short. I don't know enough about tube amps yet to know what's up.

It just sounds "right" now.

Also, I'll give a thumbs-up to Slemmons Music Services in Dallas. Everything they did seems good and they were very good to work with.
 
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Good to hear you got it back in fighting shape.

MESA runs their EL84 HOT, HOT, HOT - too hot. When my express redplated a tube I had an email exchange with MESA about it. They are running the plate Voltage at 400v and the bias at 40ma with the stock MESA tubes - yikes. They seemed to think it was OK, however everything I know about tubes says that's too hot for a push-pull configuration. But hey, they're MESA and they know better, right? They sent me 4 sets of MESA branded EL84 tubes to tie me over - I keep 'em for backups.

I ended up buying a set of JJ EL84's from Eurotubes, asking for the coldest set they had. They were still running very hot, so I modded the "fixed" bias circuit in the amp to cool 'em off a bit. The amp still sounds great, and I feel better knowing I'm not dissipating 15w per EL84. My amp is now running at 410v on the plates and 29ma of cathode current, not taking the screen current into account, I should be OK.
 
Well, the saga isn't exactly over. I was playing for several hours yesterday and one of the new Sovteks redplated. I went to standby, waited a few minutes, and brought it back. About an hour later, the volume started to drop and a different tube on the other pair was starting to redplate. Went to standby again then shut it down.

I replaced the Sovteks with the Mesas that were in the amp when I bought it. They never seemed to have a problem. I also moved the head as far forward away from the wall as I could to improve the circulation. I played for a while without any problems but I'm pissed-off and frustrated.

Fuck Mesa for their unnecessary tube-cooking design. It doesn't matter how good the amp sounds if I can't trust it. I have a freakin' Peavey Classic 50/410 that is beat to shit and has been running fine on the same set of EL84s for years. These supposed amp geniuses can't do the same?

I'm going to pick up a clip-on fan from the electronics store and see if that helps. It won't do anything about the stupid high voltage but it seemed like the Sovteks were fine until the amp got really hot. Given that this is a head, there's not a lot of room for air to circulate -- it's like a little EZ-Bake oven. I noticed too that cooling fans seem to be standard on other Mesa amps -- gee guys, any reason you couldn't do that on your hottest-running models?

Wagdog, I've read a lot about the bias mod. The amp tech was a little reluctant to do it since the bias is linked to the phase inverter. Honestly, if I'm going to have to mod it, I might as well sell it and pick up a Peavey. There's nothing that special about it to me.
 
Fwiw, once a tube redplates, it's cooked. It may work after it cools down, but I wouldn't trust it. I suspect the sovteks can't handle that voltage and/or hot bias current.

It's not so much the high voltage in the mesa (it's also high in the classic 50 - I have a c50 2x12 as well), it's the smokin hot bias current. Your amp tech could use an el84 bias plug to verify, but my express was biased with 400v on the plates and 40ma of current at idle - cooking. MESA supposedly supplies tubes that can take this abuse, however I redplated two pairs of MESA brand tubes supplied by sweetwater.

I'll have to look at the schematic to your amp to see what you're referring to wrt the bias circuit being used in the PI.
 
Just looked at the schematic for your amp.

It would appear MESA is using the bias supply voltage to also set the bias operating point of the PI. Your tech is quite correct that modifying the bias will affect the voltage on the cathode of the PI, making it run cooler. He would have change both the bias resistor and the cathode resistor on the PI to make it work - probably something he doesn't want to get into. This would also increase the voltage on the plates of your el84's, which are already seeing 400v on them (JJ tubes shows 300v as the max plate voltage on an el84 - however several guitar amps run in excess of that).

This PI circuit looks similar to the Express, except the Express is biasing the PI completely separate from the el84's bias supply - key difference.

I have to say that I'm bit out of my league analyzing what's going on with this circuit. I can read the schematic and make some sense of it, but I would defer changing any part of this circuit to an expert. I do know they are running those el84's way hot, that can't be denied. I did confirm it with my bias plug (and redplated el84 tubes). When I talked to MESA via email they basically said something to the effect of "we've been using this circuit in our el84 amps since the DC2 and haven't had any problems" - which we know is BS because the internet is now littered with people talking about redplating el84s in MESA amps and bias mods.

Also, fwiw, I found the matching in the MESA branded el84's to be horrible. I had one set at 35ma and 28ma. The JJ tubes I got from eurotubes were MUCH tighter (within 2ma or less).

If you are going to keep the amp, I would highly recommend contacting eurotubes and ordering a set of the coldest running el84's they have. Mine have been chugging along in my express for just over a year with moderate gigging and practicing. I do plan to replace them next year at some point.
 
Wagdog, I really appreciate all of the info. It matches up exactly with what the tech said and what I've been reading.

Ditto on the MESA tubes not being that well matched. The set that came in the amp seems to run fine but I have no idea how old they are. A brand-new set from MESA was way off according to the tech.

At this point, I'm going to see what I can get for the amp at GC. I realize the amp isn't broken because it's working as designed. Fussing with tubes just isn't something I want to do much. It sucks because I love, love, love EL84s but they seem to be finicky these days and I don't have the cash for a Dr. Z or something like that.
 
Guitar Center gave me an ok but not great offer. I accepted it and used the cash to buy a like-new Classic 30 head from a guy posting it on Craigslist.

Just finished playing the Classic through one of the Celestion/Mesa Black Shadows in my 2x12 cabinet. The amp sounds like it should and the Black Shadow speaker is a nice match for it. I'll probably mount the speaker in my 1x12 extension so I can have a reliable, loud, and portable rig. That was the whole idea.

Biggest headache now is both my cabs were set up for 8 ohms and the Classic only works with 16 ohms. I have a couple of junky 8 ohm speakers I can run in series in the 2x12 to hold me. I think I really like these Black Shadows -- might just have to keep an eye out for a pair in 8 ohms.

I'm kind of bummed the DC-3 didn't work out but it really was more amp than I need -- 2 channels, graphic EQ, etc. I'm better off with simple and low(er) maintenance.
 
Well, there ya go man - classic 30 is a great amp.

I had a classic 50 head and 4x10 cab - that's one I wish I had back. Killer tones. I've got a classic 50 2x12 at the place one the bands I'm in practices. Have gigged with it a few times as well. That series are still some of the most bang-for-the-buck amps out there.
 
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