Does anyone know of a mod to make separate bias controls for each tube (instead of a single bias control for the entire quad)? Or at least separate controls for each pair? I have an Uberschall Rev2 which I love - it is my favorite amp of all time. I use old stock tubes, which - as you can imagine - is getting harder and harder to find in matched sets. For example, I have a couple of dozen Mullard EL34 XF1 tubes but could select only one matched quad. The rest are matched either in pairs or in trios. If I had separate bias controls for each tube pair I could use all those tubes! So... Any info on such mod would be greatly appreciated. Thanks much.