Mesa MarkV / Saturation 'mod'

jnoel64 said:

There is nothing in the manual I received with the amp (nor the one I have already downloaded) that mentioned using EL34 and 6L6 combined. I love the idea, but kinda clueless as to what position to set for the bias switch. At any rate, the 6CA7s are sort of a hybrid anyway and are a brand new matched quad. Sure, new tubes can still be bad, I know. Yet I have never had any issue with the EH 6CA7s that I've used over the last 10 years. But, for all things, there is a first time, I know.

I could see how using EL34s in the inner slots would be fine when in 45 watt mode, since those are the tubes used then. I would have to further assume that the bias switch would be on EL34, which makes sense. But, when switching to 90 watt mode....?

I do get a noticeable change in tone between the wattage modes. The fact that I can have different wattage settings on each channel reminds me a lot of how my RK1 works with its progressive linkage. That, in itself, is an awesome feature. It would be even better if the full power/variac power could also be as flexible. Perhaps a considered feature for the VI, whenever that arrives.

I have used 2 different guitars with my initial tests. My Strat is loaded with Duncan Hot Rails. I have them set to be tap-able with a pull-push volume knob. That guitar drives my TC-50 into a fire-breathing frenzy. The other guitar tested was my HM Tele with Duncan HB-103s. That guitar has a similar effect with the TC as well. I switched to a known good cable, too. I definitely used the scoop on the GEQ. Lots of tonal power with that!

At this point, I am still waiting for the remainder of 12AX7s to arrive, and I suspect the original tubes. Yes, I know the basics of preamp tube life. That was a hard lesson in 2000 when I got a Carvin Legacy I combo. It had defective preamp tubes from the factory. Initially, I just thought the amp sucked, lol! That amp was an overall crash course in tubes for me and it sings now.

Of course, there is always the possibility something went bad in shipping and am hoping that is not the case. It was shipped in its original MB box with all the padding in place. The amp is dead quiet, no hums or buzzing. No weird volume jumps, nothing out of the ordinary at all.

As I stated earlier, once I have ALL new tubes in the preamp section (and may try some others in the power section, too), I think I will get some of the results I am hoping for.

If I can still find that broken piece from the TAD, I may have to try the jewelers glue. Thanks for the tip on that, Bandit!

I am also considering spraying the bright switch with Deoxit. Buying used gear can often be a crap shoot. I was lucky with my Dyne, but it wasn't as old as the V when I got it. No worries yet on my end.

Once all my new tubes arrive, I think I will try "stock" first and go from there. It would be the smarter thing to do to start with a frame of reference since this is my first Mark.

Click to expand...

Markageddon said:

New vid. Completely on axis. From 5-6ft cam distance.

1x12 at cam level, and 2x12 horizontal Recto cab under it. Doing the 4 0hm outs into 2x8 0hm method.
Sad but True has a Jackson V with EMGs, Standard Gibson V for the rest of it with stock passives.

Same settings as prev vid too. (After the Metallica riffs)
The beginning Metallica riffs were the typical V shape. On the graphic but with the dialled settings from the prev vid.

https://www.youtube.com/watch?v=r5F6_b2cLoE

Used a TS9 on the Machine Head riff.

Click to expand...

Dreamtheaterrules said:

Markageddon said:

New vid. Completely on axis. From 5-6ft cam distance.

1x12 at cam level, and 2x12 horizontal Recto cab under it. Doing the 4 0hm outs into 2x8 0hm method.
Sad but True has a Jackson V with EMGs, Standard Gibson V for the rest of it with stock passives.

Same settings as prev vid too. (After the Metallica riffs)
The beginning Metallica riffs were the typical V shape. On the graphic but with the dialled settings from the prev vid.

https://www.youtube.com/watch?v=r5F6_b2cLoE

Used a TS9 on the Machine Head riff.

Click to expand...

Sounds great! Nice adding the FNM riffage at 6:00 or so. Love that song!

Click to expand...

kreatorkills said:

Game changer, but...
Got a new JJ T-12AT7(say's ECC81 on tube) in V4 and it sounds incredible when it's not crackling and popping. I've tried re-seating it several times but it is intermittently crackling and popping. Has anyone else had any problems yet, or do you think it's a bad tube? Again, when it's not crackling and popping channel 3 is finally what i always was searching for!

Click to expand...

kreatorkills said:

Game changer, but...
Got a new JJ T-12AT7(say's ECC81 on tube) in V4 and it sounds incredible when it's not crackling and popping. I've tried re-seating it several times but it is intermittently crackling and popping. Has anyone else had any problems yet, or do you think it's a bad tube? Again, when it's not crackling and popping channel 3 is finally what i always was searching for!

Click to expand...

kreatorkills said:

The popping and crackling is only on channel 3. When i put back in the 12AX7 everything's good. It's either the tube is bad or my amp doesn't like the change.
Is there any reason that having a 12AT7 instead of a 12AX7 would cause a problem. What would Mesa Boogie say to this swap do you think, and why hasn't Mesa Boogie weighed in on this considering it is such a great improvement and is becoming well known?

Click to expand...

Bankim said:

kreatorkills said:

The popping and crackling is only on channel 3. When i put back in the 12AX7 everything's good. It's either the tube is bad or my amp doesn't like the change.
Is there any reason that having a 12AT7 instead of a 12AX7 would cause a problem. What would Mesa Boogie say to this swap do you think, and why hasn't Mesa Boogie weighed in on this considering it is such a great improvement and is becoming well known?

Click to expand...

My thoughts exactly .. Mesa should say something about this. I hope you understand that the warranty is void if you use a non mesa tube, so that's partly the reason. However, if you use Mesa 12AT7, it should be fine. Though I can't say how it ll behave compared to a Jan Philips 12at7 or a JJ ...

Click to expand...

APEMAN said:

I use the jan philips since the beginning of this threat and before, never had an issue with it. I think it is safe to use it - here is what mesa says about this tube type:

http://mesaboogie.com/tubes/pre-amp-tubes/12AT7.html

"...the 12AT7 can also be substituted in 12AX7 gain stages where users are seeking lower gain response from higher gain positions in the preamp string. The lower gain output of 12AT7s can expands the range of clip and overdrive potential of higher gain amps for truly authentic roots and traditional styles. ..."

Click to expand...

APEMAN said:

Markageddon said:

APEMAN said:

I use the jan philips since the beginning of this threat and before, never had an issue with it. I think it is safe to use it - here is what mesa says about this tube type:

http://mesaboogie.com/tubes/pre-amp-tubes/12AT7.html

"...the 12AT7 can also be substituted in 12AX7 gain stages where users are seeking lower gain response from higher gain positions in the preamp string. The lower gain output of 12AT7s can expands the range of clip and overdrive potential of higher gain amps for truly authentic roots and traditional styles. ..."

Click to expand...

Nice one Apeman.
Your tube is like the canary in the coalmine, being in there longer than any of ours... has it held it's characteristics and integrity well over the months? No signs of degradation..?
(I assume you give it regular usage)

Click to expand...

To my ears, it sounds very consistent, I can not hear any change in charracteristics. If the voltage is not too high (which is the case here) for a 12AT7 there will be no problem as a 12AX7 substitue, the 12AT7 is even capable of driving more current, so powerwise there is no problem as well. It just reduces the gain in V4 which results in a smoother transadmittance and therefore a smoother top end. Comparing all the 12AT7s I own, the Jan Philips is by far my favourite - and I drive it very hard, as I increased the volume 1 resistor values a bit.

Click to expand...

bandit2013 said:

It is V5A that is driving the V4B so it will not matter how hard you hit the early stages as the cut-out and clip on the V5A preamp circuit will only supply a fixed amount of signal to V4B as it cannot go any higher than the clipped and cut signal level dictated by the load line and its associated resistor and capacitors. When you clip a signal it is already at its maximum swing and cannot go any higher in magnitude.

A few of my guitars have active tone controls and the output is double that of the typical passive pickups. (0.74v typical to 1.34v on active). Even the flux drive or grid slammer will have a higher output vs not using them. Where you want the onset of clip to occur in the drive circuit (V5/V4) or on the tone stack amp V1B that feeds into V5A. Still the gain control regulates the overall input to the dual cascade. Early clip will have an effect that is good. Since I have the grid slammer (and flux drive) I have the option to hammer the cascade with clipped signal and it is very sweet to the ears. Never thought that an OD or tube screamer type pedal would have such a dramatic effect on the amp (sounds excellent thought the JP-2C as well). I have used the pedals before the V4 mod. Will have to revisit that again.

The reduced gain factor of the 12AT7 cuts out most of the upper harmonic content so you hear more of the desired frequencies in the clipped signal vs all of them that cause ice pick tone. (Shot noise is more accurate which is what it really is but more common with solid state circuits than tubes but depends on how the gain stages are designed. Originally it was discovered in tube circuits.)
Laymen's terms: Shot noise is the sound characteristic you get from high gain circuits that generate near perfect square waves (caused by cut and clip). The name came from what I recall in collage to characterize the sound in an audio circuit is the effect of taking an empty steel bowl and dumping steel shot (small bb's) into it from a distance all at once. The sharper the waveform the worse the effect which is a hard cut and clip. A better preamp circuit design that is to have clipping of the signal will have rounded off corners on the waveform (in essence lower order harmonics and greater decay in upper frequency generation of high order harmonics). Low pass filters may help as well as some tuned filter arrangements with a high Q.

Here is the nerd description, if you like the mathematics and physics of why and how it occurs.
http://123.physics.ucdavis.edu/shot_files/ShotNoise.pdf

Click to expand...