Ok, so I've been reading about people swapping for a new 12ax7 in their heads, and not noticing much difference in tone, which makes pretty good sense to me. I'm wondering though, if anyone has swapped for a different type of tube, like a 12AT7, 12AU7 or 12AY7? Here's my dillema. I sold my Ampeg SVT pro 6 because it was too heavy. Bought and love the GB, but it's not the same. The sound is very clean, and even when driven to the max, even the distortion sounds clean, if that makes any sense. Grindy, but not warm and fuzzy and rich and glassy in the harmonics. Not at all like the ampeg. I also have a markbass compressore, which, when I crank the tube gain to about 3 o clock, breaks up nicely and gets a great sound for everything from the B note on the A string up, but the notes lower than that sound like a wet fart. Too bad. Tried swapping the 12AT7 for a 12AX7 and it sounded almost exactly the same. More upper harmonic richness, but the same wet fart sound. But I digress... So, anyone tried a different tube type in their shuttle? Get a fatter warmer wooly tone? Is it just wishfull thinking on my part?