Bias mod - separate bias controls for each tube or pair???

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.

(I asked this question elsewhere on the forum at it was recommended that I ask it here).

I don't know the finer details, but the single tube biasing is available on the Ceriatone Yeti and some of their other amps. Layout available here:

http://www.ceriatone.com/hot-rodded-plexi-yeti-100/

Works really well on my Yeti.

I can't speak to how doable it is on the Überschall, but my Sound City amp has a trimmer in line with the bias lead for each power tube. That allows tweaking the exact bias voltage to each tube, with the limitation that no individual tube can get more than the supply is putting out. Should be doable with any amp, assuming one can interrupt the wires or traces or whatever going to the power tubes.

bloodspoint":13f81oz8 said:

my Sound City amp has a trimmer in line with the bias lead for each power tube. That allows tweaking the exact bias voltage to each tube, with the limitation that no individual tube can get more than the supply is putting out.

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Was this a mod on your amp or was the amp stock like that? If a mod, who did it? Thanks.