For people looking for reversing the phat mode on the TX4 rectifier board in Triaxis (Lead 1 Red channel), I put here a picture of a TX4D board which was reversed to non-phat mode - Vintage Rectifier Sound. I circled the components that have to be either replaced or added, because is difficult to see which are what component as long as the components stay right above the board notations. Here are the exact instructions on what to do (instructions taken by someone else from the Yahoo Triaxis Group):
1) Add 4 resistors:
R9 :120 KOhm
R44 : 33 KOhm
R45 : 330 KOhm
R46 : 82 KOhm
2) Add 4 disc. capacitors:
C5, C6 & C12 : 0.001 µF
C22 : 47 pF
3) Change these 2 resistors near the center of the board and labelled MID & BASS. Replace them with:
R33 (MID) : 1 MOhm
R34 (BASS) : 10 Kohm
Please note that the instructions above did not apply exactly to my TX4D version of the board, because one or two resistors and capacitors were already in place before, but if that would be the case with all TX4D or other versions, you need to change those components with others which have the above values. It might be possible that different board versions to have different component settings, but if you want the non-phat mode you might have have to put these values in the indicated place. I also believe that a resistor of 11-12 Kohm for bass will leave a little more bottom end for those liking such sound. Probably switching different values for the bass/mid resistors will also shape a different sound. I must say though, that I don't know which was the original source for these components values - hopefully it was Mesa Boogie itself!
If you decide to do it by yourself, is good to have a clamp and a solder pump available to remove the components easy and release the component's holes from excess solder. Be careful not to overburn the board or other components and also not to rip off a wire that keeps the board connected to the other boards. Have someone to help you keep the board vertical and steady while working on it. Even better, ask a tech to do it professionally - you don't want to mess things up in an expensive piece of gear.
The results are impresive and it's worth doing it. Drive and Gain rises huge, and less Bass and Highs are needed to construct Lead 1 Red tone. Most importantly, Lead 1 Red channel becomes usable! Especially for those not using a 2:90 amplifier - which was intended to complement Triaxis for loud and modern heavy playing; read about the thechnology behind 2:90 to understand better. The new rectifier sound will fit mostly metal music style, because is well saturated tone at low drive level. The more Dynamic Voice is used, the more compressed and agressive it sounds. I find a setting of 1.0 for DV is enough for my taste.
I hope this post helps. I would also like to thank Fatboy135 for his support on doing this change and other technical investigations.And here is my TX4D - non-phat - Vintage Rectifier board: