Fender Ultralinear SR 6v6 mod

[The Dude]

NOW. I played whole day this amp and I have impression, that together with voltage dropped, the sound became more flat and with less dynamic headroom. Is it possible ? I have a feeling that it actually had warmer tone before voltage drop. Kind of I feel that higher voltage on plates was driving tubes hotter what actually ended up in wider dynamic range and more sensitivity. Maybe it's just an imagination but I can kind of hear more the flatness of a solid state-recifier it has = kills dynamics. With 6v6's and more limited clean headroom it's even more obvious. Yeah, it really seems that I liked it more when the voltage was almost killing em. Now it's kind of cold in a way. Some transistor like character is noticeable somewhere. Probably this is the thing of a Ultralinears and it just sticks more in my ear, because I pay close attention .

This is odd to me. From this post you liked or are looking for more "dynamic headroom", "wider dynamic range", "more sensitivity". Most of these things would be more easily gotten with 6L6's, IMO. I'm at a loss as to why you liked the 6V6's better if this is what you are looking for. I will suggest this (partial speculation based on your description). Older Fender amps are usually biased to the cold side. You might get closer to the sound you like (warmer) if you put the 6L6's back into the amp and work on rebiasing it either by changing parts or making the bias variable. First step would be to check the bias current you have so you know where you are. Then, if not familiar, use the Weber bias calculator to get a bit more idle current to "warm up" the amp............or, maybe I just don't understand your goal.

Weber Bias Calculator