My SVP-pro preamp has been buzzing, and after taking it into the shop a while ago under warranty, they removed alot of the buzz. I ordered a set of replacement tubes from lord valve (4 chinese NOS ax7s and a AU7. I put in the new tubes. The sound is a bit different, I can't say wheather I like it better or less, but the sound is definitely different. The buzz is as loud as ever! Also, I open it up to check stuff out inside, and the AU7 in slot 4 is burning hot and CRACKED. That's right, cracked. Two pieces instead of one. (this is after a few minutes worth of playing. I take it out carfully, and just replace it with the ax7 that was in there before (dumb tech people replaced it with the wrong type hoping I wouldn't notice.) Anyways, so now I guess I have two choices of tubes, and I'm stuck with the AX7 that was in there before in slot 4 instead of a proper AU7. Both cases leave me with just as much buzz as before (although the buzz tone is different with the new tubes, but it's at the same volume. This sucks dick.