Mesa MarkV / Saturation 'mod'

[bandit2013]

I think I know what the answer will be with the 5751 in V4, it should sound about the same as a 12AX7. Since I have one (may need another to replace it, the getter flash was silver in color on the top of the tube before I tried It in one of the primary stages on a Stiletto Deuce, in a few seconds the flash turned black after I powered up that amp. I believe the tube is still good so will give it a try in V4 this weekend. Some of the long plate 12AX7 will have a similar effect but will not cure the brittle response at higher volumes and you will be limited low gain settings and reduced treble but the presence will definitely add that edge to the grind. I have used Mullard 12AX7 Long plates in V4, V5, and V6. Not bad but no way close to that amazing sound of the JP-2C. JJ ECC803s also similar as it has lower gain factor than the short or medium plate variants. The key to the right tone (in my opinion) is the JAN/Phillips 12AT7 as it adds some warmth to the gain character and reduces the upper harmonics caused by distortion. Mesa 12AX7 sounded bright but much better than the long plate variant of the 12AX7. I have used a 5751 in the V1 position with the Mark V and fell in love with the tube for use with CH1 and CH3 but changed the character of CH2 which is what I generally used for heavy metal style set to crunch voice with the gain dimed, presence just below noon, mids set to about 2pm with the bass line pointing at the mid line on the knobs and treble set to taste. CH2 has that sound but CH3 was sterile. 12AT7 in V4 makes the amp sing with CH3 and does not hinder the performance characteristic that I could tell. Instead, it provided 6 distinct voices in the JP-2C CH2 character (6 voices comes from the three voice toggle switch on the front, the pentode/triode switch doubles that number.

When I first got the Mark V I did not like the 90W character on CH3 so I basically used 45W mode with variac power and I was happy. That in itself led to some other issue as I believe I was pushing the amp harder to get the volume where I wanted it only to find I was killing my power tubes. Ever since then I ran 90W full power all the time and have not had much of an issue with the power tubes red plating but had to reduce treble, gain and presence on CH3 to have something at least usable. V4 change, different story for CH3 and gives you that boogie tone everyone is after, now it is my favorite and that stretches across the board. I still love the JP-2C but I think the change in character on the Mark V with the tube swap has placed this amp on a different pedestal and may rival the JP-2C to some extent. Had I found this magic mojo before I got the JP-2C, I may not have bought it (not true as the JP has features I wanted plus a Class A/B power amp so that was hard to ignore, in other words, I am happy I have both V and JP). Note that change in V4 to the JAN/Phillips 12AT7 does not kill off the cut or brightness of the amp, It is just as bright as the JP-2C. What it does do is regains some of the midrange that is missing in the lower frequencies and rolls off the top end harmonics (takes away the brittleness and sterile tone). I was done with the Mark V before this, was getting ready to sell it and did not expect such a huge improvement. Best of all, it has no effect on CH1 or CH2 unless you change V6 when you use the FXloop set to active. All this talk about tubes makes me want to experiment with my box of 12AX7 variants including the 5751 which does fall into the 12AX7 class due to its gain factor.

 

[Dreamtheaterrules]

12axt = 100
5751 = 70
12at7 = 60

on the gain scale, the 5751 should be much closer to what you guys are getting than what it is now.

 

[IronSean]

12axt = 100
5751 = 70
12at7 = 60

on the gain scale, the 5751 should be much closer to what you guys are getting than what it is now.

Yeah, the 7025 is the MilSpec 12ax7. The 5751 is a slightly hotter tube than a 12at7, though I can't speak for any other sonic differences. But if the reduced gain is really what's causing the change then it should work fine. I'd say give it a try, and even better order a cheap JAN Phillips 12at7 and compare them.

 

[bandit2013]

Just remember, most 5751 fall into the 70 range, JAN/Phillips runs at 90. I had to figure out where the 90 came from. Doubt I would ever find the JAN/Phillips tube. I have the GE version.

Not bad in V4 actually. Not quite as thick a response as the 12AT7 though. Still much better than the 12AX7 in V4.

 

[Dreamtheaterrules]

This is interesting because.... first the 5751 is listed as 70 on every gain chart I've seen and I've never seen one brand or another be listed as an exception with much higher gain. The 5751 is generally believe to be a BETTER sounding tube than a 12at7 (all other things being equal which is a moving target admittedly). But the 5751 is known for its quality of sound (this is the SRV tube) and is most commonly recommended to lower the gain from a 12ax7, and sometimes JUST to improve tone over a 12ax7 without giving up too much gain... And, it's the closest one to the at7 in gain (normal/average 5751 vs normal/average at7).

As soon as I started reading this thread weeks ago, I thought "if this pans out to be something, I bet my 5751 will sound even better." So... this will be interesting. But I need to get a decent at7 to compare to after I compare the 5751 vs stock/now.

Funny thing is, I REALLY want to love this amp. Sometimes I do. I got all excited the other night reading this thread and last night turned it on, and it was one of those bad nights... turned the amp on, tried two different great guitars (both PRS) and it just didn't sound that good. Harsh, and ice picky... and I've got the 2200 slider DOWN 3-4dB. Two nights before it sounded really good, but not "blow me away" good. I'm really hoping this mod works as advertised....

 

[Wayno]

I think the result of using a 12at7 in V4 has more to do with the other electronic characteristics of the tube and how they interact with the circuit than just the gain factor to be honest. The internal resistance, capacitance, current draw etc of the at7 is going to be quite different than an ax7, therefore shifting the operating point, load lines etc. It would also be greatly affected by the design of that particular gain stage and the placement in the circuit. Other applications in different circuits would not suit the at7 for the same reasons. This is why I don't really like generalised descriptions of individual valves etc as it all depends on multiple factors as to how a particular valve sounds. The end result in this instance being a quite pronounced shift of the dominant frequency of this particular gain stage from the nasty high mids to the warmer low mids which CH3 always seemed to be lacking. I like it a lot, it's all subjective.

 

[bandit2013]

That is about right.

Since there are many different varieties of the 12AX7, short plate, medium plate and long plate. Each having a unique set of mica spacers, grid wires, type of cathode (Tungsten infused with Thorium [rare], or Nickel tube with Barium and Strontium Oxide coating which is more common), heater element, plate materials and shape, getter design, etc..... This changes many aspects of the tube in general terms; impedance, Miller capacitance, transconductance, and a few other factors. That all of that in and then look at the gain stage and how it is designed. Input impedance that incudes the isolation capacitor between cascaded stages to block DC voltages and the grid resistance that forms a high pass filter and effects the low frequency gain characteristic, does the circuit have a by-pass cap on the cathode resistor, and its value will also affect the frequency response and gain characteristic, plate resistor value and then consider the plate voltage and the relation between grid and cathode voltages. It all factors in. How this applies to a 12AT7? It is in the same type or structure of the dual triode family just a different gain characteristic and grid structure, materials, etc. One factor remains apparent, the 12AT7 has a higher transconductance value than that of the 12AX7 or eve the 12AU7. 12AT7 is primarily used for current gain not in voltage gain. It will operate a bit better with the reverb circuit as that is a current driven circuit and it will change the character of the cascaded amp as it is the secondary tube in the cascade. (I am taking a long shot here....may be completely wrong ) Since the 12AT7 is more of a current gain type tube vs voltage gain type tube like the 12AX7, Since V5A is cascaded to V4B, you still get the inversion of the signal but the voltage gain does not double. It is reduced which will prevent overdriving the 5th gain stage in the CH3 path which is V3A.

Most common cathode amplifier circuits have common elements and their associated values will determine the gain affects of the circuit. Assuming that the actual circuit was designed for a specific tube characteristic, a change to a different tube will respond differently depending on how tight the intended design was made if a specific frequency response was factored in based on the original tube characteristics. How the circuit responds to frequency will define the tone of the gain character. Just because a tube has a gain factor of 100 does not mean the entire bandwidth of the signal gets the same voltage gain on the plate. I have seen many tube charts for the 12AX7 variants showing different frequency response effects (generally described for bass, mid and treble). I would assume the results were generated by a common circuit with a reference tube listed as the bench mark. You may assume if the tube that came in the amp would have a response of x, the tube chart would relate to other responses that may be possible but it depends on the design of the circuit the tube is used in.

V4 gain stage does not have a cathode bypass cap that is active at all times. If it did the gain characteristic would be stronger. However, that is where the bright switch on CH3 comes in. It is switched with a J175 PFET to ground which will improve the gain characteristic and cancel out any negative feedback in the circuit. Actually the side effect of the 12AT7 in V4 when using the bright switch has the same effect as using the grid slammer on the front end of the amp. It does shift the low end frequency response a bit and puts some emphasis on the mid to upper midrange. In other words, the bright switch is now behaving like the normal/tight switch used on CH2 and CH3 of the TC-50. The Term "bright" was a carry over from the older Mark amps as many of the controls had a "pull bright" switch either on the gain control or presence control. I think the "Pull shift" on the presence of the Mark IV did the opposite as that acted more like a bass enhancer and treble cut than the other way around. It has been a while so perhaps those cobwebs should be left alone... I do recall that when using the Mark IV at higher volumes, it was almost necessary to kill the pull bright (not really sure it had one, but the Mark III did so I may be confusing the two amps) and use the pull shift on the lead presence control (this I am sure was on the Mark IV) to prevent feedback issues. The Mark V takes care of all of that in its design but has something missing and would never have thought to stuff a 12AT7 in a latter gain stage to get the tone I was after. :roll:

Even so the 5751 tube is more of a voltage gain tube and may be a better alternative to the 12AT7. I am going to try it again since I had the amp on Extreme with the bright switch on and jumped to a quick conclusion.


Here is a link for a site I found with all the tube data sheets. For your reference if you are interested.


http://drtube.com/library/tube-datasheets

 

[bandit2013]

Aside from tying to understand anything related to tube amps, I know nothing and probably best reserved for those who do, I will digress from pretending to understand the basics and just jump to what works for me......

I decided to tube roll my preamp.. what had helped in the past is the typical miss match set of Mullard LP 12AX7 in V1 and V3, A Mesa old stock Chinese tube in V2 (does not matter for this purpose what is in there actually), Stock Mesa tube in V7, Mullard CV4004 in V5, JJ ECC803S in V6 (another long plate variant of the 12AX7) and a tried a few runs by changing V4 from the JAN/Phillips 12AT7, JAN/GE 5751 and the Stock Mesa 12AX7 tube. The results were not as expected. Note that the Long plate tubes will tent to tighten up the bottom end and since the tone stack sits between V1A and V1B why not make use of the Mullard 12AX7 ReIssue there. Also since the cascaded gain stage of CH3 ends up feeding V3A the Mullard 12AX7 also helps there too. The Mullard CV4004 is a medium plate 12AX7 variant similar to the Tung Sol 12AX7 but adds a tad more compression but does not kill the gain character or tone. The ECC803s also seems to be a quiet tube and has a slightly lower gain characteristic than the short plate JJ ECC83s (Mesa stock tube). As it seems the stock tube seems to complement the STR440 Mesa 6L6 tub so I left it as is. I tried pendode and triode modes on CH3, ran though MKII, MKIV and EXTREME settings (leaving the tone, gain, and presence controls constant). Then I flipped the bright switch played a bit and then turned it off and played a bit. Guess what tube wins in V4? (following the changes in other preamp tubes).

I know this compounds the issue due to the change in preamp tubes. I could not resist anyway as all of this tube talk tends to be a balloon of a different color. (imaging a child with a red balloon and all of a sudden he or she sees a blue balloon that is more interesting than what they have and want the other balloon, then comes along someone with a green one..... get the picture)

The winner of the three tubes used in V4 is........the JAN/GE 5751. The stock Mesa tube just gets too saturated like burred vision. Sure the complement of tubes I threw in the amp does seem to fix the thinness or lack of midrange tone but overall it is just nasty. For reference I channeled the Mark V combo into the Mesa Recto Vertical 212 as that seems to be my go to cab for everything these days and it will hurt you if the amp is too bright but will be more forgiving than the OS Recto 412 loaded with the V30 speaker as it is not as bright. I will have to try that one next.... I did run the 5751 for a while and then back to the JAN/P 12AT7. Odd that the T7 seems to cure the tone issue with the Stock Mesa tubes quite well, it did not hold true with the different array of other tubes. In other words the amp sounded too bright for my taste and the bass was more than expected. I would have preferred the Stock Mesa tube with the different blend of other tubes I am now using. The 5751 on the other hand had the best response of them all, well balanced across the board on all voices and power modes. Ice pick was gone and the amp sounded a grade above where it was before. I will have to pull all of the variants out and try again with the full complement of stock Mesa tubes just to hear the difference. Will have to wait until the tubes cool down so I can get to the ones that are hard to reach. More to come.....

 

[bandit2013]

Again with this? yes...... it is not a dead horse yet....

With the amp loaded with Mesa 12AX7 tubes, the V4 winner goes to the JAN/Phillips 12AT7. I actually like that way better than the cocktail of 12AX7 variants I threw in the amp as I found those to be a preference before tying to reduce the gain somewhere in the gain stages. The 5751 sound as bright as the Mesa 12AT7 Chinese tube when mixed in with the Stock Mesa 12AX7s. However it was better than the Chinese 12AT7 as that added some fizz to the gain character that was not enjoyable.

Sorry if this is rambling on....

 

[dlpasco]

Again with this? yes...... it is not a dead horse yet....

With the amp loaded with Mesa 12AX7 tubes, the V4 winner goes to the JAN/Phillips 12AT7. I actually like that way better than the cocktail of 12AX7 variants I threw in the amp as I found those to be a preference before tying to reduce the gain somewhere in the gain stages. The 5751 sound as bright as the Mesa 12AT7 Chinese tube when mixed in with the Stock Mesa 12AX7s. However it was better than the Chinese 12AT7 as that added some fizz to the gain character that was not enjoyable.

Sorry if this is rambling on....

keep it coming

 

[sloanthebone]

Is this what I should be looking for? JAN-Philips 12AT7WC

I just picked Up a Mark V finally I want to buy the right tube you guys are talking about. I don't want to link any sites but that is what I find when googling the tube mentioned here.

 

[Dreamtheaterrules]

Right on man. This is great!

 

[Dreamtheaterrules]

While we're on this topic.... anyone here tried the Dougs Tubes preamp cocktail for the V? I've seem some guys at TGP say it literally saved the amp for them. THey were ready to sell it and now it's the dream amp they thought it would be. I know this is all subjective. Supposedly his latest version is even better than it was a few years ago. Every time the Mark V has a bad night (like it did a few nights ago) I start thinking about pulling the trigger on that again.

Funny thing is many of the guys who swear buy it, say that they order the kit with high gain tubes and it's even better. What we're talking about here is reducing the gain staging down the road a bit.

 

[Bluestoned!]

Absolutely. Try the tube cocktail from Doug's Tubes. It's AWESOME. I did not opt for the high gain tube kit per Doug's recommendation as the V is a higher gain amp to begin with.

 

[bandit2013]

Is this what I should be looking for? JAN-Philips 12AT7WC

I just picked Up a Mark V finally I want to buy the right tube you guys are talking about. I don't want to link any sites but that is what I find when googling the tube mentioned here.

Yes that is the tube. The WC is part of the military designation. Also JAN is the first section to designate the grade of the tube is military.

What would also work but depends on how much you really want to spend on it, the tube depot has the following NOS listed on their site but may not have inventory of them: RCA, Sylvania, Tung Sol Mullard, Phillips, and Telefunken (most expensive of the lot). Most of the NOS JAN/Phillips may have been produced from 1950 up to 1980ish. Do not worry about the black pins, they are silver plated or nickel plated. The pins on the three JAN/Phillips that I have work great and the pins are tarnished. NOS RFT will also do the job and has a warmer tone to it than the JAN/phillips but is not military grade so may be suspect of mechanical noise. I have one of those too, the plates have a 6CA7 appearance due to the round holes on the plate vs the slots that are generally used. I bought those to use in my RA100's as that amp uses a 12AT7 for the FX loop that is always active and found the RFT softened the blow on the top end Vintage Lo gain channel. Reason why I bought so many of the NOS tubes, they were cheaper than the Mesa Chinese 12AT7.

 

[bandit2013]

Absolutely. Try the tube cocktail from Doug's Tubes. It's AWESOME. I did not opt for the high gain tube kit per Doug's recommendation as the V is a higher gain amp to begin with.

I tried the first set cocktail in the Mark V. That set had the Tung Sol, HG Ruby (JJ3CC83S) HG Ruby (Shuguang 12AX7AC7), three Penta Labs (shuguang 12AX7 9th gen, 12AX7AC4), Sovtek LPS. I had microphonic issues with the Penta Labs tubs and could not use them. Actually the brittleness of the Mark V was far worse than with stock tubes.

After seeing that Doug's changed the cocktail line up. I had the same tubes in my inventory and stuffed them in the V. Tung Sol, Mesa Chinese sq foil getter in V2 (recommended for heavy metal on CH2 in my opinion). I had plenty of the Preferred Series 7025 which is identical to the 12AX7AC7. Not bad. My mix sounds way better (at least in my amp using stock power tubes). V1, V3: Mullard LP 12AX7, Shuguang 80's sq foil getter tube in V2 (I have the original Mesa Chinese tubes), Mullard CV4004 in V5, JJ ECC803s in V6, Mesa (JJECC83s) in V7 and you decide if you want the JAN/GE 5751 (recommended) in V4 or use JJECC7803s. The Mesa 12AX7 also worked there as well but the 5751 really sounded better. JAN/12AT7 seemed a bit bright with the array of tubes due to change in v5 tube. It seems that the Mesa (JJECC83s) has that dark tone thing going on with the gain characteristic and blends well with the JAN 12AT7.

For Stock Mesa tubes, the JAN/Phillips 12AT7WC was more ideal. You only need one tube and leave the rest stock! Best value and end result for $15 vs $97. Actually there is nothing wrong on getting a few variants to play with. The Mark V does respond quite well with alternate tubes. I would not bother attempting the same with the JP-2C, TC-50 as it seems the design is a tight fit with the Mesa 12AX7A tube. What worked in the Roadster, Tung Sol in V1, everything else stock, or use the JAN/GE 5751 in V2 and leave everything else stock. (reduced gain in V2 keeps the tone stack from getting too hammered). TS in V1 is the better option though. It is a hard call with the RA100, Mesa tubes sound great but depends on the power tubes in use. As for the Mark V siblings 25/35, not really sure what would work as I do not have either, also not the same preamp circuits to my understanding.

This seems to be going in the Tube roll direction. Need to place a link in the Tube section however you will get more traction in the Mark V forum. I may have to experiment even further as I now have a reason to remove the chassis from the combo shell. I ordered the Celestion Redback to try out in the Mark V combo. I temporarily took out the MC90 I bought recently to see how the EVM12L would sound with the saturation mod. Just evil but I have to dial the bass out with higher gain settings using the EV speaker. Through the Vert 212 cab I can add more bass and it just sounds awesome. If I keep the EV in the combo, the alternate mix of preamp tubes and the JAN/GE 5751 is the way to go, actually that sounded sinister through the V212 cab. My preference is actually all stock Mesa tubes and V4 to 12AT7. What is cool about the Mark V 90W, you can put in almost any 12AX7 tube variant and it will sound great (may depend on what tubes you mix in as you can easily get some sloppy tone or wind up with over compression on CH3 (this will happen with Chinese square getter tubes in all positions (have enough of the Mesa tubes from the Mark III days to stuff Mark V amps but some may be past their prime) but you will get the most quite amp as the noise floor seems to disappear (CH1 and CH3 will be as quiet as CH2 with no signal and moderate gain levels).

 

[bandit2013]

While we're on this topic.... anyone here tried the Dougs Tubes preamp cocktail for the V? I've seem some guys at TGP say it literally saved the amp for them. THey were ready to sell it and now it's the dream amp they thought it would be. I know this is all subjective. Supposedly his latest version is even better than it was a few years ago. Every time the Mark V has a bad night (like it did a few nights ago) I start thinking about pulling the trigger on that again.

Funny thing is many of the guys who swear buy it, say that they order the kit with high gain tubes and it's even better. What we're talking about here is reducing the gain staging down the road a bit.

The high gain tubes, or in other words HG stands for high grade as well, generally used in V1, V2, and V3. The rest are standard grade tubes. the 7025 are not bad at all in the Mark V. Still this does not cure the brittle top end of CH3, if you have that issue you will know it.

Actually some of the Long plate 12AX7 will provide more of a high frequency roll off which helps to cut the "brittle" out of the "ness" and adds in "awesome" to it. The Mullard 12AX7 RI does this quite well, however, as is the case with most long plate designs, some can be noisy or over sensitive to voltage change when switching channels such that you hear a "ping" noise. I had two that did this but have come across many Mesa tubes that did the same thing, actually they are on the verge of going microphonic. Mullards are a better (and less expensive) tube than the Gold Lion version (Genalex B759 reissue) which appears to be identical but may have some differences. I bought one just to try out and it was a popcorn popper in the Mark V, Worked just fine in the Carvin V3MC or the RA100.

 

[dcphillip]

Hey guys, just swapped a jan philips 12at7 in the V4 position and when i turned the amp on, there was no signal. Swapped the original preamp tube back and still no signal. Don't know how I managed to break the amp doing a simple preamp swap, but the thing is ****** now. Any suggestions what could be wrong?

 

[dlpasco]

Hey guys, just swapped a jan philips 12at7 in the V4 position and when i turned the amp on, there was no signal. Swapped the original preamp tube back and still no signal. Don't know how I managed to break the amp doing a simple preamp swap, but the thing is f%&# now. Any suggestions what could be wrong?

Nothing at *all*? Did you blow the fuse some how?

I know a guy (okay, it was me) that accidentally plugged his power tubes back in wrong and swapped the rectifier tube with one of the 6L6s. The fuse immediately detonated. Fortunately the amp was okay and I had a spare tube laying around.

Beyond that, no - I can't think of anything that would have caused an issue like that beyond the usual D'ohs (guitar not plugged in, cab not plugged in or plugged into the wrong thing, mute accidentally on - I swear, I have done them all. Repeatedly).

But general preamp tube rolling is common. No idea what happened but it is probably (and hopefully) not anything serious

-Dan

 

[dcphillip]

So weird. On a whim, I pulled all the tubes and plugged them back in and now it works fine. Glad that it's a crisis averted. Interesting sound with the 12AT7. Haven't had too much time to play with it, but you can definitely crank the gain more on it. It also seems to take OD's in channel 3 better. Extreme setting is super useful now.