If the amp is working and has no sonic issues, leave it alone. HD130's run in Class AB2, favoring the "B" part of that mixture and use VERY high voltages (SVT-level) to operate. Get it wrong and you'll lose a set of tubes, speakers, and major amp components in short order. In the SVT, AB1 doesn't really apply until the driver tubes' grids are pushed positive, not so with the HD130, which Leo made as an even cleaner version of the already clean Fender Twin. If the outputs are biased any hotter (towards class A) than the tubes can take, it gets very bad in a hurry.