Possible Mark VI Directions

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dlpasco

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I'm thinking about the breakthrough from Mesa over the last six years and wondering what could be folded back into the Mark V for the next update.

The basic premise here for me is: no new features or tones, just pulling in emerging or historical technology to make the basic Mark V better.

Here's my take on it:

1. Add in the Schumacher reverse engineered power transformer from the JP-2C. At face value this seems like it should be standard on all of the big daddy Mesa amps, even if it raises the retail price a bit.
2. Cab clone (duh)
3. Keep the multiwatt, variac power and rectification options, go back to supporting EL34s/6L6 mixes again. Class A with EL34s for Channel 2 vs full power on Channels 1 and 3 would be epic.
4. Like the older Marks, retain the ability to just use a quad of 6L6s on the outside instead.
5. JP-2C/Mark-V:x5-style channel master volumes
6. Corrected JP-2C/MVx5-style fx loop
7. Hell, while we're here: we've got midi on the JP-2C, it's be nice here as well.

[added]
8. Pull Gain and Pull Presence controls - these would have been HUGE for me with my Mark V.
9. Mid boost for channel 1

All of this raises the question for me: was there any one thing that prevented to iic+ mode on the Mark V from really being a IIC+ like the JP-2C is? Are they completely at odds with being able to make a Mark IV that offers the flexibility of the V without compromising the JP-2C tone for this hypothetical Mark VI's channel 3 iiC+ mode and channel 1's Clean mode?
 
in terms of things that could have impacted the Mark V's iiC+ mode tone compared to the real deal, here are some examples of what I meant:

- smaller power transformer
- additional tone option circuitry
- additional, different channels (JP-2C has 3 channels but two of them are the same channel type with differently tweaked values)
- Power amplifier architecture
- Additional wattage options
- Variac mode
- Different fx loop

Mesa has managed to nail the IIc+ again with the JP-2C. Obviously this is a great time to get all scientific method and figure out where the critical difference really came up. It could lead to authentic but fuller featured amps in the future.
 
dlpasco said:
in terms of things that could have impacted the Mark V's iiC+ mode tone compared to the real deal, here are some examples of what I meant:

- smaller power transformer
- additional tone option circuitry
- additional, different channels (JP-2C has 3 channels but two of them are the same channel type with differently tweaked values)
- Power amplifier architecture
- Additional wattage options
- Variac mode
- Different fx loop

Mesa has managed to nail the IIc+ again with the JP-2C. Obviously this is a great time to get all scientific method and figure out where the critical difference really came up. It could lead to authentic but fuller featured amps in the future.

Ahh, the Mark VI. I don't envy mesa with the task of creating something better than the V. :mrgreen: I did do some scientific experimenting today lol. I played the JP2Cs preamp through the Vs power amp. And the V pre through the JP2C power. The JP sounds good through the simulclass power. It doesn't sound as good, but it's a difference. The JP sounded less scooped through the V. Less low end. And just a hair stiffer on feel. It had an edge to it though, the simulclass didn't smooth the JP out. I don't think the JP can be made any smoother. More upper mids. Single notes did have more of that vocal thing going on. But probably because of the said upper mids. The V through the JP..... did not sound good. It took the boxy, honky, pointy nature of the V and made it worse. I was getting some sounds like the preset EQ dials were maxed out. A very pointy, sharp attack. Not pleasant at all, and not what I was expecting.
I ran from one amps fx send to the others return. Maybe the V just doesn't like sending its signal from that point, because the sounds coming out of the combo while it was hooked up to the JP were bad as well. But bad like I had no volume. So whatever that's worth.... :?: My take away is that the Vs power section sounded better than I thought it was going to. And the V doesn't like to send its signal out to be amplified at the fx loop.

I did notice that the JP seems to get to that sweet spot at a lower volume. The V, you have to get it loud before those tubes start to rip. Even after you get the V loud, it seems like it takes a few minutes at loud volumes to sound its best. Like it needs to warm up more. But with the JP, you get great tones right away at almost any volume. And they only get better the louder you go. Also. When you dime both amps. The Vs power section gets too loose. The power tubes break up too much and your tone gets flubby and messy. But the JP stays pretty tight. Or tighter I should say. The V stops getting louder once you go past noon on the master(loop bypassed). It just gets messier, the 6l6 break up gets more and more, and bloom it does. I think one would need special speakers for those tones. But the JP keeps getting louder all the way to about 2 or 3 o'clock on the master. And it's loud. After that it's just a power tube distortion control. I shot a .44 mag one time. Besides that, the JP is the loudest thing I've ever had control of.
 
Ahhh, the mythical Mark VI....a couple of personal wishes:

1. Progressive Linkage. I never get tired of saying this. :lol: It's the one reason why I always considered the RK II the true flagship of Mesa amps, and it's also the missing link that could have turned the already great Mark V into a killer amp: ...6L6 cleans on channel 1, EL34 crunch on channel 2, 6L6+EL34 thump and grind on channel 3... :mrgreen:

2. While I get that one of the guiding principles in the design of Mark V was simplicity (as compared to its predecessors), I really miss the push-pull functionality of the earlier Marks. Surely adding (or, rather, restoring) some push-pull functionality to the pots wouldn't hurt? Or break the amp?

3. ....and, while we are at it, add (I mean restore) a separate Drive pot. To each channel.

4. Other than that, I wouldn't mind if they just made an improved version of the current Mark V. But the results might be even more interesting if they used the new JP-2C as the basis and worked it from there.
 
LesPaul70 said:
Ahhh, the mythical Mark VI....a couple of personal wishes:

1. Progressive Linkage. I never get tired of saying this. :lol: It's the one reason why I always considered the RK II the true flagship of Mesa amps, and it's also the missing link that could have turned the already great Mark V into a killer amp: ...6L6 cleans on channel 1, EL34 crunch on channel 2, 6L6+EL34 thump and grind on channel 3... :mrgreen:

2. While I get that one of the guiding principles in the design of Mark V was simplicity (as compared to its predecessors), I really miss the push-pull functionality of the earlier Marks. Surely adding (or, rather, restoring) some push-pull functionality to the pots wouldn't hurt? Or break the amp?

3. ....and, while we are at it, add (I mean restore) a separate Drive pot. To each channel.

4. Other than that, I wouldn't mind if they just made an improved version of the current Mark V. But the results might be even more interesting if they used the new JP-2C as the basis and worked it from there.


Wow, progressive linkage would instantly sell on a Mark VI. One of the reasons why I'm thinking about an RKII. Regarding push/pull, I'd like to see a push/pull pot on Ch.2 for the mid voicing. I use Mark I mode a lot with my neck humbucker, and being able to shift the mids just a touch would be great. The Mark I switch for normal/thick just doesn't cut it for me.
 
I played with a Mark V combo for a bit at the Guitar Store here in Seattle. One thing that's been huge with the recent 25 watt amps and the JP-2C is the amount of switching that has moved to the FRONT of the amp. This would be a huge win with the next update to the Mark V.

I don't always want to have the foot pedal out and switching channels is a pain when you have to reach behind the amp to do it.
 
I agree, plus get rid of the global output knob and fx loop hard bypass switch and basically just do what they have done with the JP2c with the loop.
 
Personally I don't think we'll see a Mark VI for many years, considering how long the Mark IV was in production and that Randall considers the V a compendium of Mark amps.

Funnily enough I met John Petrucci in February and mentioned how good it would be to have a Mark VB, same amp but with MIDI and built-in CabClone. He chuckled and said it would be cool.

So if Mesa end up doing that soon, I don't want to say it was my idea, but it was totally my idea. :mrgreen:
 
A lot of the new directions seem like smart moves: Midi support, etc.

But honestly the one thing I miss most is absolute insane tweakers dream that the older mark series were. The Mark V did away with the Pull Deep/Bass Shift/Treble Shift/Pull Bright/Harmonics or MidGain/etc shenanigans, and instead pared it down to it's simplest form. Now you get a toggle for the lead bright, and a toggle for combinations of those settings (you get small GEQ cap, pushed deep, etc in IIC+, large GEQ cap, pulled Deep, etc in the IV, and the negative feedback removal in Extreme.) Treble shift is locked, bass shift too, the first volume is stuck at 7.25, etc.

For the next one, I'd rather they go back to some of that insanity: Make the Gain a dual pot design with volume and lead drive. Add the pull deep, treble fat, etc to push pulls on the knobs, add one for the GEQ cap size rather than tieing it in these groups of modes. It would be less user friendly (The Mark V nailed that), but it would give back a lot of the flexibility that was lost.
 
I would also like the integrated power tube capability 6L6 with EL34 and yet retain the quad of 6l6 or el34 for more flexibility.
What would thrill me is a 2x12 combo Mark VI. (or would it? love my RA100 combo regardless of how much it weighs) There are not many speakers available that can really take the 90W. I would opt for one or two Celestion Crème ALNICO 90W speakers. So far the best speaker I have used with the Mark V combo. Sure I could settle for a 2x12 cab but I prefer the open back combo, also easier to get to the tubes for replacement.

Take a few ideas from the JP2C (dual 5band EQ sounds like a good idea), Also add another Rectifier tube for the 90W mode. Oh yeah, add a bit of recto tone to it as a selectable feature or voice (Roadster CH1 tweed is far better than that of the Mark V). Love all of the features on the Mark V except for the edge mode on CH2, still have not figured out what I should use instrument wise with that voice as it just is terrible. It has been a while since I looked at the sample settings in the manual, perhaps I will revisit it and learns something.

If Simul-class will be used, reduce the bias on the center pair as they typically run too hot, would not hurt to boost the outter pair just a tad.

Design a better footswitch jack and cable. Whatever was done on the Roadster is much better as I have yet to have any issues with the footswitch, cable or connections. would a 9 pin DIN connector with oversized thumb screws would be a better? not sure on that.
 
You can't reduce bias on the centre pair and have Simulclass. Simulclass is class A and class AB. The centre valves are class A and therefore have to be biased between 95-100%, as opposed to class AB which is typically 70%.
Mesa biased my MarkV at 95% on the middle pair and 75% on the outer pair, when using EL34's.
If it dropped below 95% it wouldn't be class A and therefore wouldn't be Simulclass. It'd be normal and very hot class AB with a transformer capable of handling both classes.

Not a fan of Simulclass myself. I like both A and AB. Just not mixed.
Peavey tried to steal someone I know's design of having a dial which balances an amp using both classes. So you can dial in how much class A or class A/B you want. I think that feature has some legs to it.

http://www.sheldonamps.com/truetone/tt3.html
 
I beg to differ, The Mark IV is simul-class and the class A circuit bias is not as hot as the Mark V. The Mark V bias on the class A circuit runs hot enough to drive EL34 tubes without using the bias switch. I never burned up tubes in the Mark IV for the 15 years I owned it, where as with the Mark V, it has killed tubes in the class A circuit many times, between 1 to 2 weeks or up to 2 months. I soon realized I could no longer use Mesa branded 6L6 tubes in the Mark V, only tubes that did not fail were SED =c= 6L6GC. Since those are out of touch now as they are out of production and I do not feel like 3 times what they are worth, I decided to alter the main bias voltage by a fractional amount and now I can run the Mesa tubes without failure. Tubes are still within the bias range for Class A as the voltage divider network on the inner to outer pair was not affected. However, the EL34 bias has remained unchanged. When the amp is in the 10W mode, the bias circuit is not used as the tubes are operated in Cathode bias vs the grid bias.
 
https://ia802508.us.archive.org/8/items/RCA_RC-30_1975/RCA%20RC-30%201975.pdf

Randal Smith's own writing on the subject, page 13.

http://www.mesaboogie.com/media/Files/MESA_Class_A_Booklet.pdf

http://www.aikenamps.com/index.php/the-last-word-on-class-a

Cathode bias has nothing to do with it. That just stipulates where the valve is biased. Rather than being restricted at the grid.

http://www.aikenamps.com/index.php/what-is-biasing
 
I did not ask for adjustable bias, I prefer fixed bias. However, my Mark V was unusable as it red plates the recommended tubes every time they are installed. It was either get rid of the Mark V or fix it. The bias on the class A circuit does not have to be set that hot to sound good, in fact, the amp was brittle in all channels especially at full power. I can only relate to the Mark V I bought new in 2012, to me it was a disappointment due to issues. However when it is operating as intended, it sounds great. The Class A amp portion of the simul-class circuit of the Mark IV was better in some respects but did seem to be lower in power delivery than the Mark V. My amp has been fixed and I no longer have immediate tube failures as I did before. I can even enjoy the 45W mode with Mesa branded tubes. I can still get the plates seams to turn red when driving the amp hard, very much the same as with the Mark IV, since the amp was repaired and operating as intended, I have yet to red plate new tubes or old one's. Still bright but not as brittle as before. Adjustment of a millivolt on the main bias voltage is what was needed in my case. I could have easily run EL34 in the center pair with the bias switch on 6L6 for 45W and probably 90W but would not be suitable for the 10W mode.

I like the Mark V, just wish my first experiences with the amp were better than they were.
 
The bias point determines what class the valve is operating in. 95-100% (though Weber claim 90% too) is what class A valves are biased to. It's all there in the links. I didn't want to state it again.
 
Could a Mark 4 owner perhaps post the plate voltage and grid current of their inner valves. That would probably help.
 
Is it really that important to debate the method by which Mesa biased the Mark V? The only time the Mark V operates in pure class A mode is in the 10W power setting, amp is reconfigured to operate at a cathode bias and uses one inside tube and the outside tube next to it. In 45W mode, the amp is operating in class A/B (push pull) but the operating point of each side is biased closer to class A than it should be for class A/B. 90W mode just pulls in the outer pair also in Class A/B. Quite similar to the Mark IV but does not have a 10 W mode. If I recall, the differences were in the plate voltages, screen resistors, and the voltage divider network on the pair of tubes. Too bad I deleted the schematics for the Mark IV after I sold the amp (you can find that one doing a search). I still have the schematics for the Mark V (not complete as it is missing the relay control circuits and logic for the footswitch, but is good enough for simple repair if needed). In essence, the Mark V in 45W and 90W is operating Class A/B. If you consider each portion of the Class A/B amplifier, each is composed of a push pull format, extended class A refers to the operating point or load line characteristic of the inner pair of tubes that is closer to that of a Class A but is not a true class A amplifier, it is a push pull or A/B. How this differs from a traditional class A/B amp is that the inner pair of tubes have a lower bias voltage than the outer pair. Inner pair of tubes have a -43.6V on the grid, outer pair have -46.6v on the grid. If you feel the Mark V is operating in Class A in the 45W mode, you are mistaken.

If you want it in writing by the manufacturer, look at bottom of page 3 of the Mark V manual.

copied from the manual:
45 WATTS turns off the outer pair of 6L6s so only the middle two are running. These are the ones with the lowered bias so, while they are still Class AB, their Class A region is extended. In Channel 3, they can be switched to run in Triode configuration which cuts their clean headroom roughly in half.
Combining these two opposite styles of wiring in one amplifier gives you the best of vintage and modern amplifier styles. Headroom and power are there when you need it… but there is always a naturally pleasing and musically curvaceous quality to the sound that
Overview: front panel (Continued)
PAGE 3
is magic to your ears and to your hands. Simul feels great and is inspiring to play!
10 WATTS reconfigures the whole set of 6L6s so that the two nearest the 5U4 run pure Class A, single-ended—no longer push-pull. This is the ultimate low wattage output circuit that duplicates the essence of the best really old vintage circuits. Here, the second harmonic (an octave above the note played) is NOT cancelled out (as it is in push-pull circuits) and provides a magical halo surrounding the notes. Onset of clip is so gradual that it’s hard to pin down the transition from clean to overdriven.

I was under the impression that the 45W mode was class A as well. It is not.
 
So basically then, Mesa are lying and Simulclass is just mismatched class AB. With 6L6's one pair biased cold cold and the other pair biased hot.
It makes sense I suppose, two 6L6's or EL34's in class A don't knock out 45watts. That is firmly class AB.
EL34's and 6L6's give about 25 watts each.

I've a headshell landing tomorrow. When the chassis is out, I'll re-check my bias measurements. Make sure I've got every variable down.
As it stands now, (cos I note everything from every amp I work on) my mk5 has the inner sockets running at

Variac, 42ma inner 28-30ma outer.
Full power 52ma inner 38ma outer
So yeah in full power 70% of max on the outside. 95% of max on the inside, in full power mode. Which Mesa say not to use with EL34's
Those were JJ's matched quad from Hotrox used about 5 times before I tried them.
I'll re-test tomorrow. But in Variac power that is nowhere near class A.
 
Mesa is not lying, Simul-Class has always been in this form. Besides, how could you run a pure class A circuit in parallel to an A/B ? This has baffled me. Extended class A region of the push pull (A/B) makes sense. However, the manual has a few references that makes you think the 45W mode is class A. There is no way possible unless the schematic is wrong, definitely is A/B in 45W and 90W. In 10W mode, only one side of the power amp is used, It still uses two power tubes (one inner and one outer). When you switch to 10W mode, the relays will change how the power tubes are wired. Quite an intelligent design in all respects. The simul-class was what moved me into Mesa, fixed bias was the other reason, along with quality of workmanship and materials, and of course the tone and character of the amp. I find it hard to believe I started with Mesa some 29 years ago.

Thinking about features, what would be cool if possible, keep the simul-class but also have a switch to change to a traditional class A/B. That would be possible since the ground leg on voltage divider on the grid of the inner tube gets unconnected. In essence, you get pure class A at 10, and two modes for high power (simul-class 45W/90W, traditional A/B 50W/100W) Since each type of power section offers its own characteristic.
 

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