I've retubed amps before and found hardly any difference; subtle stuff. Maybe a touch more high end or a tiny bit tighter on the bottom end or maybe a smidge more volume so I don't usually bother...but I'd recently noticed an amp I'd picked up SH had started to sound really flubby and had lost all its snap/punch/tightness. It was like it had become vintage in its response and it is a high gain Ironheart amp. So I ordered a full complement of tubes (2 matched JJ EL84's as they are robust and 2 JJ ECC83S and a Tung Sol 12AX7) to try out. I ended up replacing all the Ruby tubes in the amp and bang, the amp suddenly sounded killer again. It now even produces a great blues tone where before it didn't have enough sizzle and presence. Sounds funny that it could do metal but couldn't do the bluesy stuff but with the new glass, it now can do metal and blues. Notes sound fatter and sustain better with much better presence but the clarity doesn't come at the expense of brittleness. Really happy with the change and I'm glad it didn't have a subtle change like my previous experiences. I previously found that tubes 'seem' to last forever (years at least) so I don't retube often due to the cost and my prior tonal experience. EL84 tubes are dirt cheap which is a bonus so I'll make sure to do it whenever they start going off.