Mesa MarkV / Saturation 'mod'

[mace]

The Doug tubes cocktail back in 2014 worked well for me, it added a little bite/grit to Crunch. Not sure if he's selling the same cocktail today. Anyway, count me for a "yes" vote.

I have also done the AT7 mod in each V6 and V4 (only one tube at a time). Right now it is staying in V4 for a while. I need to make some comparison recordings for my own curiousity to better hear the differences it makes (back to back A-B-C comparisons). AT7 in V4 seems to help with a bit of smoothing on Ch3, but I'm always suspicious of psycho-acoustsics. When it was in V6 I didn't care for the Ch3 gain drop that resulted.

Mace

 

[Dreamtheaterrules]

so before I try this, when used in V4, are you still having to turn the loop return up, and if so, how much?

 

[soundbee]

so before I try this, when used in V4, are you still having to turn the loop return up, and if so, how much?

No v4a is the reverb send, and v4b is ch3 second gain stage. This placement you'll really only hear it on ch 3. You may want to turn your reverb up a bit. I didn't notice a difference.

It's v6b where it will affect all channels when using the loop... and a bit more on ch3 as v6a is that channel's fourth gain stage.

 

[bandit2013]

Recordings do not do it justice unless you can record actual sound such that it fills the room you are listening from a stereo or home theater system.

It is all about the feel and character that a microphone cannot pickup. Sure the tone is different and the gain or grind has the mids that you think are missing. Removal of the higher order harmonics (above your hearing level) as well as a slight roll off of the upper frequency range you can hear gives the Mark V CH3 more appeal with CH3 all of its voices and pentode/triode settings. This will also result in a different effect on the 5BGEQ, Nothing changed but the frequencies that were getting cancelled due to the secondary cascaded gain stage due to the type of feedback used are now more present (a reduction in gain will affect the feedback ratio as well, if what I assume is a form of positive feedback for higher frequencies there is little you can do about it unless you reduce the gain characteristic of the device that is used as the amplifier (12AX7, 5751 or 12AT7)

The JAN Phillips 12AT7 is actually a good tube for audio use and sure there are better choices if you can afford them.

 

[Bankim]

The Doug tubes cocktail back in 2014 worked well for me, it added a little bite/grit to Crunch. Not sure if he's selling the same cocktail today. Anyway, count me for a "yes" vote.

I have also done the AT7 mod in each V6 and V4 (only one tube at a time). Right now it is staying in V4 for a while. I need to make some comparison recordings for my own curiousity to better hear the differences it makes (back to back A-B-C comparisons). AT7 in V4 seems to help with a bit of smoothing on Ch3, but I'm always suspicious of psycho-acoustsics. When it was in V6 I didn't care for the Ch3 gain drop that resulted.

Mace

Do it !! More clips the better. I agree that it is hard to capture the sound in the room and micing cabs is just not my forte. I used the Mark V in recording my band's EP and it doesn't sound anywhere as good in the recordings as it sounded in the room during the recording process.

 

[Giz-Tone]

So after all of the above discussion and experimentation, does the V4 mod finally close the gap between the Mark IV mode and an actual Mark IV amp? Can the V now nail the tone of the IV?

 

[dlpasco]

So after all of the above discussion and experimentation, does the V4 mod finally close the gap between the Mark IV mode and an actual Mark IV amp? Can the V now nail the tone of the IV?

No idea, I’ve never touched a Mark IV. But I like it better than any of my other amps, including my IIC+.

 

[bandit2013]

The Mark V in Mark IV mode was close enough with the stock tubes, I actually liked the Mark V better as I had both for about a year.

It would be difficult to get the actual same effect of the Mark IV due to differences I the gain stage design. Also the Gain and drive controls on the Mark IV are in different locations. The only similar control of the Mark V to the Mark IV is this.....Mark V CH3 Gain control is identical to the Drive control on the Mark IV lead channel as they are located in the front of the cascaded gain stages of V5 to V4. (obvious that the Mark IV would be using V3A to V3B for this.) Also the gain control for the lead channel is fed off of the tone stack before hammering V1B. The Mark V has this as a fixed resistor network so it is pre-set.

I have stumbled upon this when I was looking for the Mark IV schematics to compare to the Mark V. Actually both are in there....Not sure of accuracy but it is close enough despite some errors... Use as a reference and nothing more.... It will help you understand the sequence of preamp tubes as the schematic is basically a road map of electrical connections. If you look at it, the Mark V flow runs from left to right where as the Mark IV flow runs from right to left once you get the page oriented so you can read it. Hopefully this link does not break any rules....but it is in public domain.

http://www.thetubestore.com/Resources/Mesa-Boogie

A reduction in gain on V4 changes the character of CH3 in such a way it matches the JP-2C CH2 and CH3 (depends on what voice you select on the V CH3).

 

[bandit2013]

Since I no longer have the Mark IV it is hard to confirm the following: Install Mullard 12AX7 Reissue into V1, V3, Mullard cv4004 into V5, Jan/GE 5751 in V4 and a JJ EEC803S into V6. I was really impressed with the tone from CH3 with this set up. It did remind me of something and it definitely was not the Mark III. Since I got a new speaker to break in (Celestion Redback) it had too much treble cut so I went back to all 12AX7 tubes. The 5751 in V4 is just a bit brighter but the distortion character shifts slightly to what I recall the Mark IV to sound like with the presence control pushed in on the Lead channel of the Makr IV. However with all stock tubes and change V4 to the 12AT7, CH3 sounds so much like the JP-2C in so many ways it was hard to want to change back as you got three flavors in the JP-2C tone arena.

One thing I did notice with the 12AT7 in V4 compared to the 5751 or the 12AX7 is I get a very loud pop when switching on the bright switch. It is basically non existent with the 12AX7 in V4. This is due to the cathode bypass cap on the V4B is enabled with the bright switch. The sudden voltage shift when the capacitor is grounded with the bright switch will make a loud pop and is related to the 12AT7 gain characteristic. Note that since the bright switch is adding a cathode bypass capacitor to the stage there is a jump in circuit gain and will be more dramatic with the 12AT7 compared to the 12AX7 tube. If and when I decide to shelve the Redback for the EV or the MC90 I will return to the 12AT7 or perhaps the cocktail of long plate tubes with the 5751 in V4. The redback speaker is not exactly what I was hoping it to be but it is very close to the Celestion Crème 90W Alnico. Heck the clean channel tone alone is worth just keeping the Redback as I have many other amps that will satisfy my high gain needs. I am no the fence with the Redback at the moment. Speaker break in is not one of my favorite things to endure.

 

[mace]

Hi,

With the AT7 in V4 in my amp, I do not get a 'pop' when toggling the bright switch when using channel 3.

Mace

 

[bandit2013]

That is good so if it is just me then no big deal....

I have no pop issues with the 5751 or the 12AX7.... I will go back to the 12AT7 (I have a few others I could try to see if it was tube related or something else) now that I removed the Red Back and have the MC90 back in the combo. At the moment I loaded the amp with long plate 12AX7 and the 5751 in V4 and I am really liking that a lot. Still the 12AT7 just is the icing on the cake for CH3.

 

[Dreamtheaterrules]

So, good news and bad news on the V4 swap attempt. Last night I dig out my tube stash. Find the NOS 5751. Good #1. While browsing through the box, I find one I'd forgotten about... NOS Mullard 12AT7! Good#2. Now I'm excited. I had played for 30 minute or so to get a last feel for stock setup, and was going to swap and try both.

Bad#1- I would have sworn Mesa said to take the front off to swap pre-amp tubes... I KNOW they did, but maybe that was in a Mark V25 thread... because I get out the powered screwdriver and remove all four screws and carefully remove the front plate. There is a black painted panel behind that one, but, it has 4 screws as well. I remove those. Nothing. I pried as hard as I was willing to with a screwdriver and that panel wouldn't budge.

A quick look from the back makes it look like you'd have to remove the tube cage and then probably pull some power tubes just to reach the pre-amp tubes. :roll: Can someone tell me if this is correct? I know tubes can be a pain to get to in small heads, but wasn't expecting this issue with a full sized head. What is the proper and easiest way to get to the pre-amp tubes? I was also going to try a Tung Sol in V1 and a Sovtek LPS in the PI... all one at a time of course. As of now, that looks like a much bigger job/hassle than I was expecting.

 

[dlpasco]

So, good news and bad news on the V4 swap attempt. Last night I dig out my tube stash. Find the NOS 5751. Good #1. While browsing through the box, I find one I'd forgotten about... NOS Mullard 12AT7! Good#2. Now I'm excited. I had played for 30 minute or so to get a last feel for stock setup, and was going to swap and try both.

Bad#1- I would have sworn Mesa said to take the front off to swap pre-amp tubes... I KNOW they did, but maybe that was in a Mark V25 thread... because I get out the powered screwdriver and remove all four screws and carefully remove the front plate. There is a black painted panel behind that one, but, it has 4 screws as well. I remove those. Nothing. I pried as hard as I was willing to with a screwdriver and that panel wouldn't budge.

A quick look from the back makes it look like you'd have to remove the tube cage and then probably pull some power tubes just to reach the pre-amp tubes. :roll: Can someone tell me if this is correct? I know tubes can be a pain to get to in small heads, but wasn't expecting this issue with a full sized head. What is the proper and easiest way to get to the pre-amp tubes? I was also going to try a Tung Sol in V1 and a Sovtek LPS in the PI... all one at a time of course. As of now, that looks like a much bigger job/hassle than I was expecting.

If you have big hands, undo the screws on top of the head that are holding the chassis in place (NOT THE ONES AFFIXING THE HANDLE). Then draw the entire chassis out through the back of the amp.

 

[dlpasco]

(I usually just fumble around inside the amp by feel and swear a lot but removing the chassis can make the process a lot easier)

 

[IronSean]

So, good news and bad news on the V4 swap attempt. Last night I dig out my tube stash. Find the NOS 5751. Good #1. While browsing through the box, I find one I'd forgotten about... NOS Mullard 12AT7! Good#2. Now I'm excited. I had played for 30 minute or so to get a last feel for stock setup, and was going to swap and try both.

Bad#1- I would have sworn Mesa said to take the front off to swap pre-amp tubes... I KNOW they did, but maybe that was in a Mark V25 thread... because I get out the powered screwdriver and remove all four screws and carefully remove the front plate. There is a black painted panel behind that one, but, it has 4 screws as well. I remove those. Nothing. I pried as hard as I was willing to with a screwdriver and that panel wouldn't budge.

A quick look from the back makes it look like you'd have to remove the tube cage and then probably pull some power tubes just to reach the pre-amp tubes. :roll: Can someone tell me if this is correct? I know tubes can be a pain to get to in small heads, but wasn't expecting this issue with a full sized head. What is the proper and easiest way to get to the pre-amp tubes? I was also going to try a Tung Sol in V1 and a Sovtek LPS in the PI... all one at a time of course. As of now, that looks like a much bigger job/hassle than I was expecting.

You are indeed thinking about the Mark V 25 (and/or maybe 35). The Mark V 90w is rear entry only (kek) and indeed it's a bit of a pain. Especially V1, with that giant shroud. Usually you only need to remove one power tube per preamp tube you're looking at, so it ended up not being as daunting as it seemed. Swapping back and fourth was quick once I'd done a couple.

Also... try not to make the mistake I did and run it with just 3 power amp tubes in. It'll work, and not immediately blow, but it's probably not a great idea. And it'll really kill you tone comparisons...

 

[bandit2013]

Yeah, Mesa missed that one.....you two options if your Mark V is a head. Remove cage, then remove on power tube that should give you access to V4 and v5 (I would pull the one closest to the output transformer). You can pull the one next to it if it helps. Option 2 would be to remove chassis from head shell but that takes longer than fighting with the tube shields.

Tip, the empty pin area on the preamp tube faces towards the front of the amp. (V3 is the only exception as that opposite in direction).

That is one reason I went from head to combo. I do not have to remove power tubes most of the time. Easier access to V1 as well.

 

[bandit2013]

Well now...let me see where to start with this issue......The pop I had been having issues with finally went away. I changed out all of the preamp tubes as some of them may have been partially used up in the Roadster cathode follower circuits. I should make a habit of marking tubes when I pull them from amps. Found some good tubes in my stash and this time I decided to use a different 12AT7 (still a Jan phillips as I have three of them to make use of). The issue was what do I stuff into V1 position. I will abandon the long plate Mullards (they are great tubes but the side effect on CH2 is not as I would have expected). Everything stock except for V4 and V1. This time why not use one of the Svetlana 12AX7 (similar to the Tung Sol, EHX, and Mullard CV4004). Clean channel sounded incredible, all voices on CH2 were usable and CH3 had the tightest sounding bass this amp ever had.

Jan/Phillips still wins..... I wonder what the 5751 will sound like in V1? Or even V6..... Some other time perhaps as the amp sounds perfect to my ears at the moment. Actually the MC90 speaker never sounded better. What to do with the Redback I wonder..... Perhaps throw it in the 1x12 cab that is too deep for most speakers.

 

[Dreamtheaterrules]

Thanks guys, I appreciate the info.

My obvious issue now is, I like to do tube swaps while auditioning. Turn everything off, swap a pre-amp tube, fire it back up and compare. Thank God my coffee roasting hobby requires an "Ov Glove" type thing so maybe I can do this without 3rd degree burns. :lol:

 

[bandit2013]

A hijack and side track to trick I used when tube rolling....

If I were tube rolling several tubes to find the best combination with a specific cab in mind, I would pull the chassis out and set it on top of the cabinet (if it fits but inverted so the tubes are facing upward. This was the case with the Mark V when I had it in head form. I would even pull the reverb tank out and set it next to the amp chassis so I can plug it in. Remove all of the tube shields and go at it. No removal of power tubes required since you have full access to the preamp tubes. I have even done this after converting the amp from head to combo but not required as much since I can reach most of the preamps without burning myself. It is better practice to leave the power tubes alone and not remove them when they are hot.

Example but a staged picture with the tube boxes just for references. This was captured when I was tube rolling the Roadster Head. The reverb tank off to the right sitting on top of the Mark V was borrowed from the Mark IV combo as that was easier to remove than the reverb tank mounted on the top of the Roadster head. The helped a great deal especially when using a different set of power tubes, tune the preamp to sound the best. Also with amps that normally have the tubes facing upward, it gives me a chance to blow out all of the metal fragments that drop down onto the circuit board with compressed air (I usually pick out most of them with a Q-tip dipped in isopropyl alcohol or acetone). Aluminum dust comes from the rotation of the tube shield into the hole to secure it especially if you have removed and replaced them a few times. Sometimes the aluminum dust will affect the amp since the DC supply is high voltage and the dust is conductive. I had this happen with my RA100 head, once channel just went to pot and lost midrange and bass. Cleaned out the aluminum dust around the tube socket and all was good. If you are going to tube roll, I suggest keeping the tube shields off until you are satisfied.

 

[APEMAN]

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