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stock marshall 1960a 4/12's sound awesome to me. Especially two together in stereo ...

Don't see why not... half drive just lowers the cathode voltage to the inverters. Don't see why it would be an issue, but get a second opinon. 'Disassembled' has studied the schematic well. It might be good to ask him as well, as I am not 100% sure, but it definately seems feasable.

I did a comparison between pulling the four center tubes out of the 2:90 and running in fulltime class 'A' and half-drive with all the tubes in. I still prefer half-drive to pulling the tubes and running in fulltime class 'A'. It sounded to brittle to me in that Class 'A' only mode. Half-drive...

Thanks! I will try pulling the four tubes as you suggested and see how the tone compares to half drive. If I like it I will just install a switch so that I can toggle back and forth.

Thanks for the tip! I imagine the amount of breakup is not as drastic as in Half - Drive. I will have to try this, it sounds like a simpler mod then the bias mods. Where did you mount your switch? Thanks! Rob

Ahhh that's what I thought.... but it doesn't lower voltage going to the power tubes in any fashion? Interesting.... I appreciate the detail of your response. Sounds like you have studied the schematic thoroughly. I agree about not passing around misinformation. Yes, it is not easy to reach...

Disassembled: You know with regards to adding four bias controls instead of two, I could put the EL34's in the class a slot really get some adjustablity. Those other mods you spoke of sound good also, especially the Class A and pent/tri switches. Anyway it all sounds cool to me.... I am just...

I agree the manual does not refer to the actual mechanics of how half drive works. But the explaination of the effect on tone and how the 2:90 reacts with half-drive engaged is indeed accurate. It would be interesting to know what Mesa has to say about how half-drive actually works. I would...

Straight from the Simul-Class 2 Ninety Manual. BTW the 2:90 is a power amp.

My main guitars are: Gibson Les Paul 60's Classic Re-issue Texas made Charvel's Ibanez UV-777 & String Carvin dc120 12-string electric

I have electronics experiance plus I do know how to measure bias current. I could probabaly just jump in myself and do it. However, I would like to get insight from someone who has done this b4. I do have an experianced tech at my diposal but he doesn't have experiance with the Mesa 2:90. You...

Already have the tubes that I want. Been wanting to do the bias mod for a while that way I have adjustability over the PA tone even more. I want to experiment with bias hotter versus colder. Once I am done I will know what I want. I have the Schematics for the 2:90 from tube freak, however they...

why don't you try running in half drive? I have been running in half drive for years with my 2:90. Here's some the benefits: PA Distortion at lower volumes More controlled feedback More Compressed tone for leads Better Feel Don't Wake up the neighbors The only thing I have not liked is the...

I am afraid he's right... we need a closeup of circuit board TX4 which is on the top at the back of the unit. Also your photos need to be alot bigger than the ones posted too. The bigger the better... :) Rob

I figure I better put this one at the top again. I am hoping someone nows where to find the info. Thanks! Rob

Triaxis into a Simul-Class 2:NINETY into a marshall 1960a in stereo. For effects I run a TC Electronics G-Force in the effects loop as well as some foot pedals before the TA.

I have bought new Groove Tube Matched JJ 6L6's for my Simul-Class 2:ninety Power Amp. However, upon following the recommendations of a tech @ Mesa I think I purchased a set that is too cold for my tastes. Not to worry, I think if I modd the fixed bias of the 2:90 to an adjustable bias setup I...

On my 2:90 I have a pushbutton switch installed in place of the jack because I just run halfdrive all the time - no need to switch it in and out. You could just create a shorting jack plug out of a 1/4" phone plug by soldering the ground to the center. Modern boosts low lows and adds specific...

Hi all, My setup is this: Gibson Les Paul Classic with Seymour Duncan JB Bridge Pickup Triaxis TC Electronics G-Force Simu-class 2:90 4/12 Marshall top cab 1960A Settings for dirt: gain: 10 treble: 9-10 mid: 10 bass: 0 -3 lead drive : 3 - 4 master: 4.5 - 5.5 DV: 1 Mode: lead 2 yellow or lead 2...

MSI - Thanks for your help. Those photos definately solve the riddle of the modifications I have on my triaxis. And they also confirm what others have been telling me here about what they are. :) However, it does not solve the hum issue. Does anyone know where I could check component-wise for...