New to me Mark III Blue Stripe (need your help)

[DC3 Gridlock]

Hi all, I sold my Mark IIB back in April and picked up a near mint Mark III combo last weekend. It is a Simul-Class model, has an EVM12 speaker, and reverb.

I've had a lot of trouble taming the excessive brightness of this amp. I've tried the Mesa recommended settings and these settings would just make the amp even brighter, more brittle sounding, and with very raspy overdrive.

Today, as a last resort, I pulled V1 and swapped it with V2. This changed seemed to help the tone a little bit.

I then pulled the two outer EL34’s and swapped them with a match set of JJ 6L6’s. This seemed to bring back much needed bass and added some “Fender like” sparkle to all three channels. The amps sounds good.

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I ran all 6L6’s in my Mark IIB Simul-Class, and I read that Mesa did not recommend doing this with the Mark III, but I prefer the tone of the 6L6’s… Should I be worried?

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One thing that I recently noticed is that both Volume 1 and the Bass knob cause a severe volume drop once I turn either knob past 6? Does this make any sense to anyone?

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Maybe this volume drop problem has caused my issues with excessive brightness with this amp?

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Any help is appreciated.
Thanks,
Grid

 

[Sixtiesvibe]

Just from a theory side.....

Pushing the tubes seems to be causing a volume drop from what I read. So to me I would start at one of these two points. V1 feeds pretty much everything after it. If that tube/tube socket or anything related to V1 is a place to start.

Next thing is bass needs more power than treble. If V1 and the bass control are causing volume drop then it might make me think I might have a power supply issue. If you try to turn the master up a bit does the amp sag and lose power? That's a clue as well that it might be power related.

Please understand this is only from a theory perspective. There are a few guys around the forums from Mesa who can narrow this down very well. I am sure they will see this and be able to help more.

GL, these are great amps.

 

[DC3 Gridlock]

Just from a theory side.....

Pushing the tubes seems to be causing a volume drop from what I read. So to me I would start at one of these two points. V1 feeds pretty much everything after it. If that tube/tube socket or anything related to V1 is a place to start.

Next thing is bass needs more power than treble. If V1 and the bass control are causing volume drop then it might make me think I might have a power supply issue. If you try to turn the master up a bit does the amp sag and lose power? That's a clue as well that it might be power related.

Please understand this is only from a theory perspective. There are a few guys around the forums from Mesa who can narrow this down very well. I am sure they will see this and be able to help more.

GL, these are great amps.

Thanks Bottle Rocket for your reply.

Just to clarify (I have since edited my original post) the volume drop issue happens with both the Volume 1 and Bass knobs, when I turn either of them them past (6) six. I may have confused the issue as stating V1 (Volume 1) with the V1 tube.

Any easy suggestions of things to check as being a power supply issue? I do own a multi meter but I am not a tech. I may pull the chassis this weekend and look for anything that may appear to be a damaged component.

I do doubt that the filter caps have ever been changed in this amp, after being nearly 30'years old, since the amp appears to be in such mint condition. Could old filter caps possibly cause this volume drop and brightness issue?

I appreciate your help. I am hoping at this is not a power supply issue and just somthing very easy to correct. If I can get this volume drop issue corrected, maybe it will fix my brightness issue with the amp.

I really want to like the amp and if I can get it sounding like I think that it should sound, from the many good comments I've read about the amp, it could be a keeper.

Hope someone has had a similar experience with this amp and can share the fix.

 

[dlpasco]

Thanks Bottle Rocket for your reply.

Just to clarify (I have since edited my original post) the volume drop issue happens with both the Volume 1 and Bass knobs, when I turn either of them them past (6) six.

Hope someone has had a similar experience with this amp and can share the fix.

Boy, that does NOT sound okay. I have not noticed any volume drop at all turning those knobs up. That's probably worth taking it in to get looked at.

What channel are you on when you're seeing this happen? What about the fizz? Or does this happen across the board?

A lot of people keep the presence down around 2 on these amps, with good reason. I like to turn the presence up towards 8 or so if I want a really singing neck pickup soloing sound, but that's about it.

Running all 6L6s sounds WAY better to me. The worst thing that will happen is that your power tubes may wear out faster, but the amp itself can take it just fine.

 

[kdorsey]

I'd contact support, that's not normal. Once you get thing to normal operation and you're still not happy with the brightness, here's what I did:

1.) throw all typical settings advice out the window. Start over from scratch.
2.) I tamed the brightness with NOS RFT 12ax7s in V1 and V3.
3.) unplug the stock EV12L. Buy a new cab of your tonal preference and load it with a vintage voiced speaker. One of my favs (had it in my combo cab for a couple of years) is the WGS ET65.
4.) switching to 6L6s warmed up your amp? Not me. Buy a fresh set of EL34s and try again.

If you don't like the character of old RFTs, do the research and make the swap. Traditional Boogie tubes are bright as hell, to me. And when in doubt, those sliders on your EQ work really well. :mrgreen:

Your MkIII is virtually bullet proof. Experiment...it can take it. Impedance mismatches won't hurt it. The power tubes will wear faster, but who cares if it sounds like what you want? Change speakers a lot. It's easy and relatively inexpensive. Read up on different preamp tubes and the infinite tonal options available. But first, get it professionally fixed. Good luck!

 

[GJgo]

Here's what you do. Get a call tag to send it back to Mesa. Have Mike B. go through it to fix any issues, do a re-cap job, and do the C30 mod. You'll spend a few hundred bucks. You will then love the amp & it will be good as new.

I have done this. The C30 mod tames the fizz & makes the presence knob useful. Makes it closer to a red stripe. I run my presence on 4 now, prior I was on 1 maybe 2 due to fizz.

 

[el34sg]

Mark III's are crazy bright with the treble past 3.
Especially the Green & Blue stripes.
I can get my green to sound almost identical to my red stripe with the presence
on 1 and slight tweak of the GEQ.

Some people can have the presence up a bit more and not have an issue.

 

[GJgo]

FWIW I've actually been working with diming the presence & then pulling the high end back with the GEQ. I think it opens it up. It sounds crazy till you try it.

 

[Wyzard]

yes, I do that too on occasion, just to mix it up - presence high, and 2200 and 6600 pulled down on the GEQ.

 

[McBarry]

Like sixtiesvibe, my mind went straight to failing powersupply too..
Orig filter caps ?? change 'em.. Ditto bias and to lesser extent cathode bypass caps.
Excessive brightness - is it poss the amp has little/no bottom and thus SEEMS mega-bright ?
Use Line out - does volume drop in the slave amp ?
Use fx return - does volume drop still occur when signal pushed ?
These simple things can tell U a lot..

Regs, Dave