It's long past time to change the tubes on my amp. I have purchased the 1 12AU7 and 4 12AX7 tubes, but when I open up the amp, the old tubes don't say anything on them (I bought this amp used from a friend) and I have no idea where the AU7 goes. I have searched the net and these forums and haven't been able to find a schematic for this particular amp. I have found SVT pre-amp and poweramp schematics, but nothing specific. Does that matter? Do all SVTs use the same schematic? Thanks in advance for any help! This is an excellent forum!