Preamp tubes for slower/softer clip in Mark V

[The Mink]

I love love love my Mark V. But I figured out exactly what could be better about it, and I’m wondering if tubes could make it happen.

I find that the weakness of the V is that the transition to clip is a bit sudden. Compared to my Lonestar, Cali Tweed or King Snake, I find that it gets dirty pretty quick in all modes and as a result doesn’t handle boost pedals, fuzz etc nearly as well.

I wonder if there are some 12AX7s out there that are known for a more organic transition into clip? Let me know if this makes sense!

 

[Eevil]

Howdy.

You could check this thread first:

Mesa MarkV / Saturation 'mod'

 

[The Mink]

That is an overwhelming amount of discussion... WOW

 

[bandit2013]

Yep, the Saturation mod does a nice job for CH3. Actually, the Mark IIC mode sound more accurate.
However, it does not address the other two channels since that gain circuit is not used in CH1 or CH2.

JAN 5751 in V1 will curb some of the early clip on all channels. I would not bother with a current production 5751 but the NOS 5751 will be more ideal. I have also tried that in V4 along with many other preamp tubes. The JAN Phillips 12AT7 does a great job in V4. It aids on reduction of the higher frequencies and yet retains the gain characteristics of the lower frequencies.

In that thread I went too far, even started modifying the amp. That is not necessary unless you have an ice pick generator like my V was. I could not use CH3 due to the ice pick issue (had to dial out presence and treble all the way) but the Saturation mod really works. It also gives you more range in the gain control due to the lower gain characteristic of the 12AT7. You will also hear a slight change in the reverb since the other half of V4 is used as a driver for the tank.

If you want to reduce the gain characteristic of CH2, V2 is one option. Some long plate 12AX7 tubes will have a lower gain character than the short plate version. JJ ECC803S is one example. It has been such a long time since I used the Mark V, forgot how it sounds. I have some other 12AT7 tubes I should try out and see what happens. I bought a NOS Mullard 12AT7 for the bass amp but did not like it. Tried it in the TC FX loop, it was ok, a bit darker in tone. The JAN Phillips 12AT7 so far has the best sound in many of the other amps that use a 12AT7 tube. Tempted to fire up the V and see what else can be done with it.

One thing to note: The Mark V does respond quite well with preamp tubes. It is one of the most tunable amps I own. I should probably pull the chassis out as I found the power tubes to feel a bit oily or wet. Not sure what was up with that but fear I may have a leaking power cap. Don't want to feed it any juice until I can confirm what may be electrolyte was just moisture due to environment.

 

[Ran7Bari]

I would start with trying a NOS GE or JAN 5751 in V1 & a Sovtek 12ax7 LPS in the phase inverter to find out if it makes a difference for you.

 

[The Mink]

Yep, the Saturation mod does a nice job for CH3. Actually, the Mark IIC mode sound more accurate.
However, it does not address the other two channels since that gain circuit is not used in CH1 or CH2.

JAN 5751 in V1 will curb some of the early clip on all channels. I would not bother with a current production 5751 but the NOS 5751 will be more ideal. I have also tried that in V4 along with many other preamp tubes. The JAN Phillips 12AT7 does a great job in V4. It aids on reduction of the higher frequencies and yet retains the gain characteristics of the lower frequencies.

In that thread I went too far, even started modifying the amp. That is not necessary unless you have an ice pick generator like my V was. I could not use CH3 due to the ice pick issue (had to dial out presence and treble all the way) but the Saturation mod really works. It also gives you more range in the gain control due to the lower gain characteristic of the 12AT7. You will also hear a slight change in the reverb since the other half of V4 is used as a driver for the tank.

If you want to reduce the gain characteristic of CH2, V2 is one option. Some long plate 12AX7 tubes will have a lower gain character than the short plate version. JJ ECC803S is one example. It has been such a long time since I used the Mark V, forgot how it sounds. I have some other 12AT7 tubes I should try out and see what happens. I bought a NOS Mullard 12AT7 for the bass amp but did not like it. Tried it in the TC FX loop, it was ok, a bit darker in tone. The JAN Phillips 12AT7 so far has the best sound in many of the other amps that use a 12AT7 tube. Tempted to fire up the V and see what else can be done with it.

One thing to note: The Mark V does respond quite well with preamp tubes. It is one of the most tunable amps I own. I should probably pull the chassis out as I found the power tubes to feel a bit oily or wet. Not sure what was up with that but fear I may have a leaking power cap. Don't want to feed it any juice until I can confirm what may be electrolyte was just moisture due to environment.

I appreciate the perspective! I’ll be trying this out right away and reporting back.

 

[mace]

I can vouch for the JAN 12AT7 in the V4 position as making a difference. One loses a bit of drive but the amp sounds a bit sweeter.

 

[Nandrewjackson]

After a critical listening shootout I've found the new production tung sol AX7 is the best all around new production I've tested. *** I'm not counting any cryogenic or gold pin tubes in my opinion, standard, tested tubes only. ***

I haven't tried the electro harmonix 7025 although I am excited to do so.

I do not recommend changing types. From AX7 to AT7 or 5751. It won't physically hurt the amplifier, but the amplifier wasn't designed for them.

 

[mace]

I should mention the 12AT7 in the V4 position only affects channel 3. If I recall correctly a 12AT7 in V6 position will affect both channels 2 and 3. Give them a try!

 

[bandit2013]

If you are using the FX loop, the 12AT7 will affect all channels.

In my opinion, the Mark V I have is an ice pick. It has been that way since day one. I blame this amp for wanting to experiment with tube rolling. Never did such with the Mark III I owned for 24 years or the Mark IVb I had for 12 years.

I used to have the same thought on running only 12AX7 tubes. However, it was not possible to make use of CH3 extreme, MKIV or IIC+, CH2 edge, or CH1 clean/tweed as they were all sub-par sounds I could not tolerate. Ice pike with the presence and treble dialed out all the way. Midrange also reduced and dropped the gain to 9am or just to where it almost cuts out the sound. I should have returned the amp as it was a lemon from the start. I have also red plated many Mesa branded STR440 tubes and the only saving grace were the SED =C= 6L6GC. Bias voltage was askew and not where it should have been. Overheating issue other than red plating tubes was the other common issue. Chassis would get so hot you could not touch it. Thankfully the screen resistors decided to burn out. Bias was corrected and screen resistors replaced but did not fix the ice pick tone. The 12AT7 in V4 was the saving grace for the CH3. Still had ice pick character in tweed and edge. I just basically gave up on the Mark V about the same time I dropped out of the forums. However, what does work in the 12AX7 format to help cure the ice pick blues of the Mark V for those that suffer the same fate as I got with mine, Mullard 12AX7A reissue long plates in V4, V5, V6. That helped to some extent but still had to dial out the treble and run the gain at the cutoff point. Since I did some circuit mods, that fixed most of the ice pick issues I had with the CH3. I have installed the stock tubes and it was better but not what I would expect from a Mark series amp. If you can find it, a NOS RFT 12AX7 does a wonderful job in the V4 position. It does have a similar tone to the Mesa branded JJECC83s but the gain characteristic is much different. Low gain it is darker, moderate gain it is a beast without the extended high frequency ice. I still have the Mark V90 but no longer use it. My poison has been the Royal Atlantic, Triple Crown, Multi-watt Dual Rectifier, Roadster and Badlander. Still have the JP2C too but got hooked on the other amps. Badlander for me is tops as I get the rectifier sound and Mark lead tones I could not get with the JP2C or Mark V. Sure I have played through other Mark V90s and thought they sounded great. Mine was just one of the duds that should not have been released for sale. Biggest disappointment for me. Probably why I have no interest in the Mark VII. I would still like to try one out one of these days, and my perception on the Simul-class blunder of the Mark V90 would be eliminated. Mark III and Mark IVb never had any issue. Sure, I have gone through many power tubes with the Mark III over the 24 years of ownership. Never replaced the tubes in the Mark IV for the 12 years I owned it. I did not play much over that period due to injury but it never let me down. The JP2C restored some of my faith in the Mark series amps. Feel my interest has been lost in favor of something else Mesa has provided.

 

[bandit2013]

I guess it is too late to edit. I meant was if you use the 12AT7 in V6 it will affect all channels when using the FX loop. You can ignore the rest of the post above.

 

[ATR1]

What year MarkV do you own that disappointing you?