I picked up a used 2 Channel "H" combo a few weeks ago and can't find much info on it and the tubes. My question regards the use of the 12WD7 and it's role. Now I'm assuming that this tube is the phase inverter (it should be considering the physical location). My question would be why they used this tube in this slot and if any damage would be caused by swapping it out for a balanced 12AX7. Also, might anyone know how the tube topology is used in this circuit? Such as, V1A feeds the clean channel which then, after the gain and tone controls, goes directly to the input of the first 12AT7 of the reverb circuit. I have yet to pull the chassis. As for the amp....man is it honest! Unlike my other amps, I can clearly hear the differences between the various guitars and pickups that I have. Not that my other amps are shabby at all....they just don't show the huge diffence as this one does. The power tubes have to be swapped out though. The tubes it came with were so far out of match (20+ mV plus) that I couldn't bias it properly. I swapped in a pair of Sovteks that are within 3 mV of each other but they sound rather dull and "cardboard-ish". Nonetheless, this amp has a lot of tonal options and has some great sounds in it. Thanks for any tube info!