Mesa MarkV / Saturation 'mod'

[sherrillsml]

This mod may be Mark V production lot dependent. Not really sure what changes have taken place over the years since 2009. So far I have only used the one JAN/Phillips 12AT7 and have not had any problems with it. My Mark V was made in 2012 if that matters. So far all is good (knock on wood). I would say I have at least and estimate of 50+ hours on mine with the 12AT7.

I would personally be weary of using a non military grade 12AT7 as the JAN version will take some abuse as it was designed and selected for military service under hash conditions.

sherrillsml, did you actually put the 12AT7 in the phase inverter in either of your Fender amps or are you indicating it will sound terrible if you do as you can do it but have yet to do so? Perhaps I am reading into things too much.

What tube type of 12AT7 are you using? It could be related to the tube, when it was manufactured and brand as many tubes were made in many locations over the decades of not longer.... I would prefer the unused versions of the NOS JAN/Phillips vs one that was tested good but had been used. I have seen many places selling used tubes but tests good. If you are getting a hum, it could be the heater element in the tube. Non-coiled heater elements are better than the coiled versions as tubes with the coiled heaters had given me grief with that issue (12AX7 tubes with coiled heaters Tung Sol, EHX, Mullard). I found I could not use them in V3 in the Mark V as the hum would creep up after a week of use. CH1 was always noisy. Once the hum set in the tubes were useless in other amps as well.
Also what other tubes are loaded in the preamp if you do not mind me asking?

It is what it is, not all mods work in all amps, especially if there were changes made during the production years that may seem transparent to the end user until something like this thread comes along. Have you tried a 5751? I also have a preference for the JAN/GE 5751 but they are a bit expensive compared to current production 12AX7 and 5751.

Thanks for the input bandit. I purchased my amp new in 2010 and it was made in May of 2010. To answer your question pertaining to the at7 tube manufacture one was a new Jan/Phillips, one was a new JJ, and the third was a used Grove Tubes. As to the condition after they started to have the ~60hz hum, they pop and hum when placed into my Fender amps. Lastly I have always been partial to long plate ax7s and my preamp is mostly loaded with Sovtek 12AX7LPs.

Thanks also for the 5751 info, I may grab and try one of those. I really just need to open the amp up and do some diagnostics since most everyone seems to be able to do the at7 mod without experiencing my problem. I hope it is not a manufacturing date issue because you and apeman really made my Mark V usable again. I think my issue with it pre-mod was similar to yours in that it had an ugly high frequency response that was only partially negated by other tube rolling. I feel with this mod that the Mark can finally compete with my Marshall JCM800 and my Super Reverb.

 

[bandit2013]

This mod may be Mark V production lot dependent. Not really sure what changes have taken place over the years since 2009. So far I have only used the one JAN/Phillips 12AT7 and have not had any problems with it. My Mark V was made in 2012 if that matters. So far all is good (knock on wood). I would say I have at least and estimate of 50+ hours on mine with the 12AT7.

I would personally be weary of using a non military grade 12AT7 as the JAN version will take some abuse as it was designed and selected for military service under hash conditions.

sherrillsml, did you actually put the 12AT7 in the phase inverter in either of your Fender amps or are you indicating it will sound terrible if you do as you can do it but have yet to do so? Perhaps I am reading into things too much.

What tube type of 12AT7 are you using? It could be related to the tube, when it was manufactured and brand as many tubes were made in many locations over the decades of not longer.... I would prefer the unused versions of the NOS JAN/Phillips vs one that was tested good but had been used. I have seen many places selling used tubes but tests good. If you are getting a hum, it could be the heater element in the tube. Non-coiled heater elements are better than the coiled versions as tubes with the coiled heaters had given me grief with that issue (12AX7 tubes with coiled heaters Tung Sol, EHX, Mullard). I found I could not use them in V3 in the Mark V as the hum would creep up after a week of use. CH1 was always noisy. Once the hum set in the tubes were useless in other amps as well.
Also what other tubes are loaded in the preamp if you do not mind me asking?

It is what it is, not all mods work in all amps, especially if there were changes made during the production years that may seem transparent to the end user until something like this thread comes along. Have you tried a 5751? I also have a preference for the JAN/GE 5751 but they are a bit expensive compared to current production 12AX7 and 5751.

Thanks for the input bandit. I purchased my amp new in 2010 and it was made in May of 2010. To answer your question pertaining to the at7 tube manufacture one was a new Jan/Phillips, one was a new JJ, and the third was a used Grove Tubes. As to the condition after they started to have the ~60hz hum, they pop and hum when placed into my Fender amps. Lastly I have always been partial to long plate ax7s and my preamp is mostly loaded with Sovtek 12AX7LPs.

Thanks also for the 5751 info, I may grab and try one of those. I really just need to open the amp up and do some diagnostics since most everyone seems to be able to do the at7 mod without experiencing my problem. I hope it is not a manufacturing date issue because you and apeman really made my Mark V usable again. I think my issue with it pre-mod was similar to yours in that it had an ugly high frequency response that was only partially negated by other tube rolling. I feel with this mod that the Mark can finally compete with my Marshall JCM800 and my Super Reverb.

Best of luck to you getting a resolve on the amp. How long do the LPS tubes last. Those are coiled heaters as I have them too. A bit lower gain than the Mullard RI but those also help in cutting out some high treble issues. They did not work very well with the 12AT7 but the stock mesa tubes do. If you are using long plate tubes, the 5751 would probably work out better as I had tried the JAN/GE 5751 and found the stock tubes made things bright but the long plate tubes evened everything out and was close to the V4 Mod (12AT7) with mesa 12AX7 every where else. (Mark V + stock tubes + v4 [12AT7] = JP-2C or very dang close it is hard to tell the difference). Still not sure the hum issue, I would try them in the Fender first it good, see what happens in the Mark V. I am suspecting a PS issue somewhere. How long do your power tubes last? The plates get the full voltage and the screen resistors on the power tubes feed from the save voltage as the V4 (reverb circuit). Voltage difference is the choke voltage drop. Have you ever had the screen resistors replaced on your amp in one of your services issues? That was the first thing that blew out on mine. Just curious and no need to fill this thread with issues some of us have been troubled with. I am still wondering why I kept mine this long. But at least it is working and I can take advantage of the V4 mod.

 

[Markageddon]

In 25w news:

Rectifried just did the swap. Noticed the difference immediately, even going through a cabsim...!!
Seems ecstatic.

More and more I play with these amps now, more and more I think a lot of people may have been quick to judge Doug West during the smallcap/large cap debate era. Its now glaringly obvious he told us absolutely no lies in that manual, and when more of this gets out, a lot of 'em are gonna be taking their hat off to him.. When you read through it all now it fits the words perfectly. Especially the part about it being authentic IIC+. All of the care they took to get this amp the way it is, has paid off and is announcing itself proudly everytime I plug in.

Im hatless right now.

\m/ \m/

 

[bandit2013]

This ice pick tone could have been remedied in the design itself that would not require a 12AT7 to do the job. Just a minor change in plate resistor and delete the grid to cathode capacitor and you would have the original Mark IV cascade circuit, Mark IIC+ and would also be close to the Mark III. I have found several of the schematics and looked for the drive circuit. The last tube in the dual cascade has the same plate resistor 270K (same as Mark V) but all three do not have the grid to cathode capacitor on the secondary stage. There is a grid to cathode cap on the primary (first stage of the cascade pair). This cap will increase the gain of the stage but will also bump up the higher frequency along with increasing the harmonic content. Having both stages similar is just compounding the high order harmonics. I am almost thinking of finding this cap on the V4 circuit and cut one leg off or at least de-solder it and find out what the end result would be with a 12AX7 in V4. Unfortunately the available schematic on public view is the 2009 version. The 2010 is not available. I am not saying to start cutting out components in your amp as this may or may not prove to be a viable thing to do. I just have a hunch, nothing more.

Since I will be pulling the Mark V chassis out today to swap speakers (yeah, again with the speaker thing) I will try and see if I can find the grid the cathode cap, if it looks easy to remove I may do just that. Hoping it is a disc cap vs axial leaded bead cap as that would be easier to remove from the PCB once the glue has been cut (most likely will be glued to other components next to it to prevent vibration damage to the leads). Perhaps I should not have said anything and do it first...... Still in debate If I want to do this....

 

[bandit2013]

Bummer, Hope you were not waiting for any response to my last post as I did not get around to pulling the chassis out yet.

 

[Bankim]

Bummer, Hope you were not waiting for any response to my last post as I did not get around to pulling the chassis out yet.

Hey Bandit, no worries. I have been a been occupied over the weekend due to family and stuff, so no update on the hum thing yet... It would be nice to know if your observations are correct, regarding the cap. whenever you have the time to do the needful..

 

[Dreamtheaterrules]

In more V25 news:

I did the swap with an old Mullard AT7 that sounded great in every amp I tried previously. Put it in V2 and was VERY concerned about the Crunch channel effects, as I love that channel. This is an awesome sounding tube that I've been saving for the right thing...

My quick preliminary update is... Crunch sounds EVEN BETTER! Turn the gain up just a little and you have the same gain as before. But even better tone! I'm sure the Mullard has something to do with it, but it's not just that. And, all three modes of C2 are significantly better! After 15 minutes of being blown away by an even better Crunch, I switched around on C2 for a while and remember thinking "THAT is the Mesa tone I fell in love with years ago, and have been trying to get ever since!" Just richer tone than before.

I normally try not to swear in public, but I'll have to give this a HOLY $HI%!!!!!! Do not hesitate, do not pass GO even if you get to collect $200. DO THIS NOW! I always thought the V25 was great. Now it's AWESOME!

 

[Markageddon]

In more V25 news:

I did the swap with an old Mullard AT7 that sounded great in every amp I tried previously. Put it in V2 and was VERY concerned about the Crunch channel effects, as I love that channel. This is an awesome sounding tube that I've been saving for the right thing...

My quick preliminary update is... Crunch sounds EVEN BETTER! Turn the gain up just a little and you have the same gain as before. But even better tone! I'm sure the Mullard has something to do with it, but it's not just that. And, all three modes of C2 are significantly better! After 15 minutes of being blown away by an even better Crunch, I switched around on C2 for a while and remember thinking "THAT is the Mesa tone I fell in love with year :mrgreen: s ago, and have been trying to get ever since!" Just richer tone than before.

I normally try not to swear in public, but I'll have to give this a HOLY $HI%!!!!!! Do not hesitate, do not pass GO even if you get to collect $200. DO THIS NOW! I always thought the V25 was great. Now it's AWESOME!

Hahahah Told ya. Nice one, and congratulations. Yeah Crunch is unearthly now, just have to dial it harder like you said. It handles tonnes of mid/boost dial now too. Rest assured that the swearing is standard reaction thus far. All part of the adjustment/equalisation process. :mrgreen:

 

[bandit2013]

Finally got around to pulling the chassis. Spend about an hour looking for the mysterious capacitor that eluded my ever poke and prod. The reference designators (those that are visible). Kudos to the designer of the board to make things quite difficult to locate. It is packed though so the reference designators under the parts would make sense. Oh well, so much for that as it was not worth the risk pulling the wrong part. Installed the MC90 and about ready to close the book on this amp. I am slowly getting back to the love/hate thing again. It was fun while it lasted. I just do not find it as satisfying as the JP-2C or the TC-50. I doubt I will sell it unless something else comes along. For now it goes back into hibernation for a while as I want to spend more time on my other amps like the poor old Roadster. Tubes in that amp have not seen the heat of current flow in the heaters for a while. The JP-2C has the same issue, cold and unfired for a while as I was forcing myself to use the Mark V. Also have the TC-50 at my disposal sitting next to the Mark V. It is what it is and not exactly what I want it to be. When is the Mark VI coming out anyway? Or is there something else in the works that will empty my wallet?

Enjoy the Saturation Mod with your V. A note for those who wonder, the MC90 sounds great with the Red Back running parallel. The top end is really getting better with the Red Back and I may just stuff that into the combo just for S&G once I think it is broken in a bit more. I will be here or there as I am not going anywhere.... just taking a step away from the Mark V for a while.

 

[mace]

Prescence is cool on the big amp. On channel 2 crunch especially. It had next to no effect on the highs. Just the rawness and in your faceness of the mids. Loving the way it works now. Edge mode is killer now too.

Hi,

I thought the AT7 mod (in V4 or V6 position) had no effect on channel 2 (on the 90W Mark)?

 

[IronSean]

Prescence is cool on the big amp. On channel 2 crunch especially. It had next to no effect on the highs. Just the rawness and in your faceness of the mids. Loving the way it works now. Edge mode is killer now too.

Hi,

I thought the AT7 mod (in V4 or V6 position) had no effect on channel 2 (on the 90W Mark)?

Markadeggon has been playing with it in the Mark V:25, and in that amp the equivalent tube to the Vs V4 also does the job of the Vs V2 which affects Crunch.

 

[Markageddon]

Prescence is cool on the big amp. On channel 2 crunch especially. It had next to no effect on the highs. Just the rawness and in your faceness of the mids. Loving the way it works now. Edge mode is killer now too.

Hi,

I thought the AT7 mod (in V4 or V6 position) had no effect on channel 2 (on the 90W Mark)?

Markadeggon has been playing with it in the Mark V:25, and in that amp the equivalent tube to the Vs V4 also does the job of the Vs V2 which affects Crunch.

Indeed I have been playing the V25 a lot. (Sorry I was away, much obliged Sean.)

And on my 2010 90w too. And yes its V4'd up. Maybe presence just isn't affecting that range anymore. Can do a vid showing it, if more proof is needed, but it definitely works like that on mine in 10w mode...!! (Put the sliders into an aggressive V too to give the old characteristics every chance to show up...but nada)

Maybe the 2010/post 2010ers have differing signal flow/tube order...? I have no idea, and if the more tech savvy guys have any comment on this, Im all ears.

 

[bandit2013]

Gain stage sequence has not changed since 2009. Models prior to 2010 (not sure on date exactly or what range of SN are affected) have a different tone stack on CH3. Also other tubes in the preamp will affect the character you are getting from the amp and on CH3. Change in V1 usually wakes up the beast in more ways than one. I am finding that I need to reduce the presence as it still has the same effect but a bit less since the ice has melted in the tone.

How old are your power tubes? The Presence is pulled from the OT transformer and sent back to the phase inverter circuit. The signal never makes it any farther into the early gain stages so its feed back effect is based on load to some extent but will be influenced by weak power tubes if they are on the "should be changed as they have been there since I bought the amp" or have been long time since they have been replaced.

 

[Markageddon]

Gain stage sequence has not changed since 2009. Models prior to 2010 (not sure on date exactly or what range of SN are affected) have a different tone stack on CH3. Also other tubes in the preamp will affect the character you are getting from the amp and on CH3. Change in V1 usually wakes up the beast in more ways than one. I am finding that I need to reduce the presence as it still has the same effect but a bit less since the ice has melted in the tone.

How old are your power tubes? The Presence is pulled from the OT transformer and sent back to the phase inverter circuit. The signal never makes it any farther into the early gain stages so its feed back effect is based on load to some extent but will be influenced by weak power tubes if they are on the "should be changed as they have been there since I bought the amp" or have been long time since they have been replaced.

About 6 months on these ones in the big amp.

Interesting. Thanks. \m/ Maybe the poweramp is just reacting then to the changed set of frequencies in the preamp.
The effect remins me of the way Prescence loses its omnipotence when in Extreme mode or something. It still does add walls of deatil and range, but its not as pronounced in the usual way at all.

 

[bandit2013]

I forgot to mention it is also dependent on what tube is in the PI position. Presence will not be as dramatic if the tube has lots of high frequency roll off like you would get with the Mullard RI 12AX7 (long plate) or the Sovtek LPS. I have experimented with many different tubes in the PI location. In most of my amps anyway. Mark V seems to get a reduced level of top end with a long plate tube but the Roadster gains some top end. It could be related to the center pair running in an extended Class A (push pull) which is not the same thing as a Class A/B. However, the outer pair of tubes running in 90W mode is class A/B. With an extended Class A (push pull) power amp you will get both clip and cut when the tube begins to be overdriven. Class A/B you will only get clip since the load line has a very small slope angle it will not go into cut-off (when applied signal drops below the load line of the tube circuit as it will be transferred to the opposing tube by the phase inverter at that point.). Perhaps it is too early for me to be thinking audio amplifier stuff.....

For those who asked about the Big V 90W, if you only use the 12AT7 in V4, the effects are limited to CH3 only with some slight change in the reverb that will affect all channels but may not be noticeable. If you are using a 12AT7 in V6, the effects will be noticed on all channels if you are using the FX loop in active mode to run the global master volume control as this will reduce the gain factor of V6B which is used to raise the FX return level back to normal signal level to drive the phase inverter since it was attenuated by the transistor circuit (part of the 5BEQ summing amp which is all solid state). The V6B circuit is not designed to add any distortion but will be clipped if the return is signal is higher than expected. If you place the FXloop into hard bypass, the 12AT7 will only affect CH3 since the V6A is the master volume control for that channel. Channel 1 master volume controls the gain level of V3B and Channel 2 master volume is derived by V3A. In hard bypass, both CH1 and CH2 will not pass though V6B so there is no effect on them by the 12AT7.
Note that all channels will pass though V3A and from that point, relays will direct the signal path based on channel selected.

The tube that defines the distortion for CH2 is V2. This tube position adds pre overdrive to the channel before the tone stack (similar to a Rectifier amp circuit but is only a single gain stage). Once the signal gets into clipping the effect will transfer to the other remaining gain stages. Reason why the Mark I mode is do dark in tone since the boosted levels of bass signals are enhanced considerably. Also why the crunch sounds so beefy and chunky and with higher gain settings, boosted mids, nominal tremble and adjusted bass can drive the CH2 into chunky metal mayhem far more than CH3. I found this to be more pleasing than the Roadster running Modern on CH4. I just could not get CH3 to perform as good as it was lacking harmonic content and adding high order harmonics that just sounded like (insert poo emoji here).

I think that is great that there is some benefit for the 12AT7 in the Mark V:25 or 35 but there will be some sacrifice to the other channel as there is no signal avoidance to the V2 tube as both channels use it.

If you have one of those tube driven OD pedals that use a 12AX7 and if the gain and tone character is too much try a 12AT7 in there instead. Just wonder if that would have a similar effect or not.... Hard to tell actually as I do not have any of those.

 

[IronSean]

That was a longer version of what I was trying to say, which is that the tube that acts like V4 in the 90w is V2 in the 25w. But where in the 90w the other half of the tube is a reverb return, where in the 25 it's the Crunch mode tube that makes it Crunch. So in the 25 you can't affect one without the other.

Bandit is also right that V6 affects all channels, but the talks of needing to raise the gain on Crunch were related to the 25w.

 

[mace]

That was a longer version of what I was trying to say, which is that the tube that acts like V4 in the 90w is V2 in the 25w. But where in the 90w the other half of the tube is a reverb return, where in the 25 it's the Crunch mode tube that makes it Crunch. So in the 25 you can't affect one without the other.

Bandit is also right that V6 affects all channels, but the talks of needing to raise the gain on Crunch were related to the 25w.

Thanks, all, for the clarifications. I thought my ears were deceiving me since Ch2 did not appear changed after putting the AT7 in V4 on the V:90.

Mace

 

[Markageddon]

That was a longer version of what I was trying to say, which is that the tube that acts like V4 in the 90w is V2 in the 25w. But where in the 90w the other half of the tube is a reverb return, where in the 25 it's the Crunch mode tube that makes it Crunch. So in the 25 you can't affect one without the other.

Bandit is also right that V6 affects all channels, but the talks of needing to raise the gain on Crunch were related to the 25w.

Thanks, all, for the clarifications. I thought my ears were deceiving me since Ch2 did not appear changed after putting the AT7 in V4 on the V:90.

Mace

Ive given to the possibility then, that it just sounds better now that Graphic settings that sound great for channel 3 now sound great for channel 2 simultaneously. Most of us, myself included favoured channel 3 in our slider setting priority bias, slightly compromising our channel 2 voicing in some way, or vice versa. Thats a HUGE game changer in the way that crunch seems to have been enhanced. By having channel 3's voicing more akin to Crunch with all that low end and grind. Could be that by switching to channel 2 after playing 3 for a while, I may have confused surprise at it already seeming so perfect, with change. Crunch has always been badass. And now switching to channel 3 feels more of a logical continuation of channel 2. And thats what I was hoping for.

 

[Dreamtheaterrules]

My preliminary findings were that with the V25, the Crunch channel gain was affected, but with the gain up just a little it matched the previous level of gain, so no loss there, and the tone was even better than before! I've always LOVED the crunch channel on the V25, in fact, way more than I like it on the Mark V. I think that Mark V crunch channel is really good. I think the V25 crunch channel is GREAT! And now, with the V2 change, maybe even better.

I've only gotten to try it one night though. I had to leave town for a family medical emergency the night after I tried it. Also note, the change to C2 was obvious and significant improvement! The change to C1 (it only affects the crunch mode) was a little loss of gain, easily compensated for with the gain knob, and tonally better. The possible caveat that the AT7 I happened to have is an old Millard that sounds great. This tube alone would make the amp sound better, IMHO, but the effect on C2 is more then gain change and tonal shift that results from the gain reduction. Plus a little old Millard mojo on top.

I honestly can't wait to try this on my big Mark V. But I may not be home for a few days and will give the V25 a more thorough test before I try the Mark V swap.

 

[bandit2013]

Well, there is a way to get awesome tone from the CH2 Crunch on the 90W model, Change V2 on the Mark V:90W. That is the gain stage mainly responsible for OD to some extent as the rest of the gain chain does contribute as well. I am not suggesting a 12AT7 (dang it now I have to try that but doubt it would do anything on the 90W amp). Long plate 12AX7 (mallard or JJ). Medium plate 12AX7 (mallard CV4004, Tung Sol, EHX, Chinese Ruby 7024), heck just try any variety of 12aX7 and see what happens. It is interesting to note that the Long plate versions will push the bottom and mids a bit more and roll of the top, Medium plate tubes (depending on which one) will seem to scoop the mids a bit (CV4004), and the short plate like the Mesa or the Chinese square foil getter tube from the late 80's will pump up the top end. What I like about the CH2 on the Mark V:90W amp is that it has the least amount of white noise (typical hiss when the gain is boosted). It gets even better when using an alternate power tube (EL34 or KT77) vs 6L6. That reminds me to get out the Gold Lion KT77s again. :shock: I was using those for a while but before the Sat Mod.....

I do like the affect of the sat mod (V4=12AT7) with the Mesa STR440 6L6 power tubes the best. I had switch to a different variant as the Mesa tubes I had were rattling something fierce when using the clean channel. Not fond of the low frequency rattle especially if it is louder than the volume I am playing at. Why the Mark V does this with just about any tube and does not do it in other amps, Simul Class vs Class A/B? Only time it disappears is in 10W mode. Reason for my decision to step away from the V for a while. If I was using the 412 cab I would not hear the tube rattle as much but it is always present no matter what cab or just combo speaker is in use. I normally play the Mark V generally loud so I do not have to listen to the tube rattle which is annoying. It is what it is. Just about every amp I had with Simul Class power amp did the tube rattle. Mark III, Mark IV. I do not get that with the JP-2C, Roadster, RA100 (unless the EL34's are crappy) or even the TC-50. Sorry that would be another subject matter all on its own. No need to bring it up hear.....but I did.... oops. :|