90W Mark V becomes the BEST Mark with preamp tube tweak?

[dlpasco]

If you haven't followed this thread (http://www.grailtone.com/forum/viewtopic.php?f=33&t=73352), Apeman and Bandit2013 outline how a few preamp tubes changes can transform the big daddy Mark V into everything it was ever meant to be.

The original title of the thread wasn't particularly clear, so I thought it was worth calling out directly.

I've made this change: I put a Tung Sol 12AT7 in V4 and a JJ 12AT7 in V6. Total cost: $40 after tax.

I used to say that my Mark V was the best Mark I had, if I had the fx loop off. No longer. It's better than it's ever sounded before, with the fx loop engaged, on all three channels. My JP-2C has been collecting dust as I *prefer* the tones I'm getting from my V over it.

I've been using Fat mode on channel 1, Mark I mode on channel 2, and mostly IIC+ mode on channel 3. They all sound fantastic.

I've also been using extreme mode, which now sounds better than it's ever sounded on this or any other Mark V variant I've ever owned.

If you have a 90 Watt Mark V, I'd suggest trying this out. If you have a JP-2C or a bone fide IIC+ to compare to, I'd like to know how you think it stacks up.

 

[Wayno]

Absolutely agree.

Also curious as to how this would stack up on the 25 and 35 versions as I would assume the preamp sections are very, very similar? Maybe unnecessary, but I'm still curious anyway.

 

[IronSean]

Absolutely agree.

Also curious as to how this would stack up on the 25 and 35 versions as I would assume the preamp sections are very, very similar? Maybe unnecessary, but I'm still curious anyway.

The effect happens by changing the behavior of the 4th and/or 5th gain stages of Channel 3 on the Mark V, which are V4B and V6A respectively. Now, this means it'll also affect V4A and V6B, but those are the Reverb send and Effects return stages, so should be minor if unnoticeable affects. (Actually, I just realized the effects return might be part of why the V6 change seems to tame the loop on performance).

In the 35 (and presumably 25 isn't a different layout, I didn't check) Those 4th and 5th gain stages are V2B and V5B. Now, V5A is the effects return as well, so V5 is about the same as V6 in the Mark V, so you should get the same performance. V2A is the 2nd gain stage of the CH1 CRUNCH mode though... so the lower gain and difference in character might adversely affect your CRUNCH mode, you'll have to try it to see.

Also, I ordered a couple of the JAN Phillips Gray plate 12AT7WCs myself to try out in my Mark V.

 

[jnoel64]

I am curious if other Mesa amps would benefit from an AT7 in the final gain stages....

 

[dlpasco]

I am curious if other Mesa amps would benefit from an AT7 in the final gain stages....

Apparently some people like putting them in for the phase inverter in Mark III’s (and some people don’t).

I decided to try it myself on my Mark III earlier this week and I think it’s going to stay. I find it to be smoother and that I actually am okay with using EL34s with the AT7 in place.

 

[elpingua]

12at7 ordered x2! Lets see how it goes.

 

[Bankim]

Just tried the V4 mod with a JAN Philips 12At7 and IIC+ mode has become a beast. Highly recommended. Thanks to Apeman and Bandit.

Going to try the V6 change only or both V4 &V6 after I get a hang of this. IIC+ mode sounds gorgeous though.

 

[Wayno]

Just tried the V4 mod with a JAN Philips 12At7 and IIC+ mode has become a beast. Highly recommended. Thanks to Apeman and Bandit.

Going to try the V6 change only or both V4 &V6 after I get a hang of this. IIC+ mode sounds gorgeous though.

Does doesn't it 8)

 

[Dreamtheaterrules]

"The Best Mark?" Ok, now it's official. You guys are killin' me here! :lol: :lol:

So, holiday weekend coming up and yet another rainy one. :roll: :roll: Should get to try the V4 swap some time this weekend.

And, at first the feeling was V4 was better than V6 swap. Are you guys now feeling that swapping both is better than just the V4?

Edit to say: I've been on the bubble about my Mark V for a couple months now. In that couple months, I've only played my V25 a couple times with my new EBMM Cutlass, so dialed for strat tones. I've felt since I got the Mark V that if it just sounded as good as the V25 but with the girth and authority of the big Mark V, it would be my dream amp. The V25 just sounds fantastic! MUCH better than the big one. The gain is just fantastic, and no ice pick/cold clip or other nastyness. I played the V25 last night and it only renewed those feelings. If this mod makes the Mark V sound like "that" only bigger, it will be everything I'd hoped for when I bought it. You guys are really making me think that it could be that great.

 

[bandit2013]

Just do it..... Hopefully you will not let any smoke out of the tube when you do.

I can only imagine what this would sound like with a good Mark V, mine has had some issues over the years and I do not believe it is up to par with the rest. However, I was on the verge of selling it or just placing the whole dang thing out with the trash as I was that fed up with the amp. Seriously I could not do much with it (except for the Celestion Crème 90W speaker helped considerably in the combo). Still the tone was lacking so I pulled the Crème 90W out and bought an MC90 just to sell the amp. After getting the JP-2C I had lost any reason to keep the Mark V..... Also got the TC-50 when the Saturation Mod thread started or I was lead there by Apeman.... the rest is history..... Dang does CH3 sound awesome mojo madness now. Still I do not regret getting the JP-2C as that is just as much fun to play through as the Mark V has become currently. My V may be an oddball as I am only doing the V4 = 12AT7. At least that preserves CH1 and CH2 with little effect other than reverb (some claim it has changed, I cannot tell the difference as it is as loud as before on each channel).

 

[Dreamtheaterrules]

well.... not a DROP of rain over the weekend or the holiday, so I spent time outdoors working on my sunburn. 8) If the forecast is correct though, we now have about 8 days in a row with over 50% chance, so maybe I'll get some indoor time in soon.

 

[Thaymz]

I put in the Jan Phillips AT7 in the V4 and V6 yesterday. Very pleased with the results.

The tone definitely sounds more raw with increased harmonics. I mainly use c+ mode and the harmonics side reminds me of how the amp sounds running in Class A in the 10w mode. I never really had an issue with FX loop or ice pick tone, maybe because I run through an attenuator at lower volume, so can't really say there's an improvement there. I have noticed additional noise though coming through as I run 4CM with an axe fx. The noise levels were quite low prior to the change, now its really noticeable.

Given I run 4CM and don't really dislike running through the FX loop is it worth keeping the V6 in there? Could it be that tube contributing to the additional noise?

 

[Wayno]

I would defo try either V4 or V6 as well as both. Also swap out the AT7'S when you try it as one might be noisy, therefore causing your issue. There really is no right or wrong way to run this simple mod. V4, V6 or both, it really is up to your own preference.

 

[Thaymz]

I would defo try either V4 or V6 as well as both. Also swap out the AT7'S when you try it as one might be noisy, therefore causing your issue. There really is no right or wrong way to run this simple mod. V4, V6 or both, it really is up to your own preference.

Yeah will try a few combinations on the weekend.

Does everyone take out the reverb tank to change the preamp tubes? This was my first tube change. Getting them out was easy enough but was difficult to ensure the pins were lining up when replacing. Just curious if I should be removing the tank as well.

 

[IronSean]

I don't, just take out the power tube most in the way and reach around. Though bandit raised the nice point in another thread that if he's doing a lot he'll just remove the Chassis instead, placing it upside down on top of the amp shell. Then it's nice and easy to swap back and fourth.

 

[dlpasco]

I usually just grope around blindly and swear a lot when I swap preamp tubes on my heads.

That's the nice thing about the Multiwatt Dual Rectifier: that head has a TON of open space in it, really easy to work on.

 

[bandit2013]

I have taken out the tank, but it is a nasty thing to put back in as those rubber bushings tend to fall out and do not stay in place. What does help re-installing the tank is the tooth picks with the plastic decorative fringe or a Q-tip with one end removed. Shove the tooth pick or mangled Q-tip into the T-nut from the bottom, pop on the rubber bushings and then followed by the plastic spacer, tank on top, and carefully insert the strews in the front of the amp and install one screw at a time. It can be done but is a PITA sometimes. Not necessary to use the tank as I have often just pulled the chassis out and no tank connected.

I got used to pulling the chassis as I do not like burns on my fingers. Even the winter pair of gloves I used have shriveled up. Guess they were not leather.

Instead of pulling the tank, you may be able to get a long RCA ended stereo cable that can be separated or use two long one's if you have them. Note that one is not a coax cable on the Mark V and the wire gauge is much thicker than what you would find in an audio cable. If you decide to just connect something else to reach the tank and leave it in the shell, remember which plug goes where.....

If you are just going to swap V4 and or V6, just let the power tubes cool down and pull then for access. However if you want the full potential and you changed something like different power tubes or speakers tube rolling the complete preamp may be ideal but will take time once ear fatigue sets in as it all sounds the same at that point.

 

[Markageddon]

"Yes...very possibly!" would be my answer to the title.

And the V:25 also, if your put the same tubes in V2.

Did this this week, after success with the v4 mod for my 90watter.
The 25 absolutely roars like it's daddy and has similar effect on the gain structure, the playing feel and the 'ballsier channel 2 with smoother highs' character. Channel 2 matches Channel 1 better, for my tastes. Extreme is fluid and oh so addictingly playable. Again just like the big amp mod.

Have every reason to believe it works therefore on the 35 also, as the tube duties, according to the online manual, are the same as the 25..
Feeling absolutely set for life, between the 2. Never been happier with my amps.

Mesa/Boogie for life.

 

[Bankim]

With respect to changing tubes , specially the preamp V1 V2 V3, I found it best to turn the amp upside down and let it sit on where the handle is, so that you end up pulling the tube up and out instead of down. Plus you get to see the tubes this way. And I do remove all the 4 Power tubes, the rectifier doesnt get in the way so I leave it as it is. I have changed the pre-amp tubes a few times and I find that having the amp this way makes it way easier then trying to change it in the amps normal sitting position.

 

[Thaymz]

I ended up landing on V4 as my preferred position for this tweak. Took out the v6, felt that it did something weird to my CH2 presence.

Channel 3 is sooooooo good, although I loved it to begin with.