Hey guys, here's a heads up. I replaced the tubes in my ampeg svp-pro with 4 Ei gold (12ax7) tubes and one Jan/Phillips (12au7). The sound is much clearer and tighter but still sounds warm and growly. You can get away with not changing the 12au7 as long as there is at least an EH tube in that position, but it made a noticable difference. The 12ax7's made the most difference. Especially in the first gain stage. The ones in the eq position made a smaller difference but the tone was sweeter with them.