I'm talking about one of each in each channel...I think somebody has to ask these questions. No question that 2 matched pairs of different tubes in each side is no biggie and results in what you described, but what I'm proposing is much weirder, and probably illegal.
Tube mixing
So what would happen (theoretically anyway) if in a "push pull" tube amp where each tube has its own bias pot, you stuck disparate tubes next to each other. I have 3 sets of power tubes...if I put 6550s and KT120s next to each other in each channel biased properly (or to the amp specs), or a KT88 next to a 6550 in 1-2-1-2 pairs...would this trigger cosmic calamity? Gear meltdown? Audio magazine subscription rejections? Would the tubes sit there and stare at each other in disgust? I'm not necessarily gonna try this, but it seems to be a way to get the advantages of different tubes ALL AT ONCE! Ha...and hmmmmmm....