Try it with Pentode and Triode. Wow. I have lost complete interest in using the Mark V before this mod. Either Clean on fat or CH2 Crunch was the only selections that had any merit towards keeping the amp vs selling it. Now I am really liking the Mark V more than I ever imagined. This boogie now has the Mojo it was missing from day one. Actually it makes the Mark V CH3 a multi voiced JP-2C. Triode mode is amazing with all voices. Perhaps I am happy I held onto the amp as there was a solution for the Mark V icy blues (not regarding music style). I can blame this on my exposure with the Mark III and Mark IV and for some reason the Mark V was not living up to its reputation. Perhaps many who love the amp never had the privilege to play though the older amps that make the Mark series what it is. The Roadster was also the V killer as well as the RA100. Still, the CH2 with the gain maxed was the ultimate heavy metal chugger especially when running a quad of Gold Lion KT77 though a pair of 8 ohm EV speakers running on the 4 ohm output. The Roadster could not even come close to that sound. The JP-2C had the tone and gain character I have been searching for all this time. Now the Mark V is on Par with a few tricks up its sleeve. I can also run the amp though the V30 speakers and love what I am hearing. I could not stand the tone of the V30 before with this amp. Had always thought it be the speaker and not the amp. Wrong. The ice pick tone only gets worse with the EV as it is much louder. The Celestion Crème 90W ALNICO was one that did make a difference as it has more top end roll off.
I have played a newer Mark V when I was in NJ to try out the new TC-50. I did not notice it having the ice pick tone on CH3, it actually sounded really good but I was playing though it at a reduced volume level. However with the simple mod, my icy mark V is a monster that it should be at any volume setting. I normally use the FXloop active to use the master volume. I should try the FXloop off and see how that sounds. I could not tolerate it that way before, that may be different now. Change in V4 Still has plenty of bite with the bright switch off, adds a bit more with the bright switch on but not brittle and lacking the full midrange control. Seems that the 12AX7 in V4 tends to shelve the upper frequencies and harmonics and dampens the lower mids and sounds like you are playing though a tunnel or under a blanket. I have tried many 12AX7 tubes in this as well as in V5. The long plate Mullards did help a bit but still harsh in terms of top end character. JJ long plate ECC803s helped a little too but still not the same. The JAN/Phillips 12AT7 is the key in this solution due to its warmth compared to the Chinese verion that Mesa uses in the RA100 and TC-50 for the FXloop. There are other options if you are willing to pay the money, actually most are quite reasonable (except the Telefunken Diamond Bottom ECC801s as I could buy a new guitar for that price). I would personally stick with military grade for this application.
I have played a newer Mark V when I was in NJ to try out the new TC-50. I did not notice it having the ice pick tone on CH3, it actually sounded really good but I was playing though it at a reduced volume level. However with the simple mod, my icy mark V is a monster that it should be at any volume setting. I normally use the FXloop active to use the master volume. I should try the FXloop off and see how that sounds. I could not tolerate it that way before, that may be different now. Change in V4 Still has plenty of bite with the bright switch off, adds a bit more with the bright switch on but not brittle and lacking the full midrange control. Seems that the 12AX7 in V4 tends to shelve the upper frequencies and harmonics and dampens the lower mids and sounds like you are playing though a tunnel or under a blanket. I have tried many 12AX7 tubes in this as well as in V5. The long plate Mullards did help a bit but still harsh in terms of top end character. JJ long plate ECC803s helped a little too but still not the same. The JAN/Phillips 12AT7 is the key in this solution due to its warmth compared to the Chinese verion that Mesa uses in the RA100 and TC-50 for the FXloop. There are other options if you are willing to pay the money, actually most are quite reasonable (except the Telefunken Diamond Bottom ECC801s as I could buy a new guitar for that price). I would personally stick with military grade for this application.