There have been a few Hammond reverb amp conversions on here. I elected to remove the negative feedback, I'd been advised that I would like this and it seemed to be good on one or other amps that I tried. Anyone else done this or anything similar? I added a standard ECC83 gain stage and although it works great there is far more gain than I need. Reinstating the neg feedback, possibly making it switchable seems a good start. However, when I replaced the original patch, with its original resistor the amp started making a horrendous low frequency thumping sound. I have never moved so fast in my life pulling the power out. What could that be?