*warning, warning, warning...if you dislike subjective descriptions...avoid, avoid. avoid this post!....*
This is pure subjective anecdote, so worth only as much as anyone here paid for it...
But just to report my own "experience:" I tried tube rolling for the first time this year - pandemic, stuck inside, bored, finding things to fiddle with in the system. I've used mostly Conrad Johnson tube amps for 20 years but whenever it came time to replace tubes I just bought whatever CJ recommended. The sound stayed quite consistent, it seemed to me. I started with my CJ Premier 16LS2 pre-amp which takes six 6822 tubes. Expensive for tube rolling! I tried some different NOS tubes that got good notices, but it seemed to change the tone in a way I didn't like, especially exaggerating the high end, sibilance etc. So that was a loss.
My CJ Premier 12 monoblock power amps (140w/side tube amps) had come with 2 GE 6FQZ tubes and 1 GE 5751 small input tubes. They were the originals that came with the amp so due for replacement, but I tried some other NOS tubes I'd read about somewhere. The sound went more lush, but turned in to sludge. It sounded soft, like what you'd get with a speakers with an underpowered amp. So I tracked down the same NOS tubes that originally came with the amp and...voila! The speakers "woke up" and the original sound was back, tight, punchy, energetic, which was a relief.
Then a while back I happened upon a really good deal from a guy I know selling a pair of CJ Premier 12s that were newer than mine, and had been thoroughly gone over and "updated" at the CJ factory - they had the expensive "Teflon Caps" replacement tweak some CJ owners pay a lot for. Since I could get these amps at not much more than I'd get for selling my old pair, I grabbed them, if only to have a better condition set to replace my old ones.
I was surprised that they seemed to sound damned different than my originals! The sound seemed to just expand in every way - the soundstage, the imaging, the bass depth, everything sounded "bigger" and more expansive like someone had just replaced my speakers with slightly bigger speakers. It was pretty wild. I was skeptical this had anything to do with the expensive Teflon Caps so the first thing I zeroed in on was that these new amps came with different output tubes - KT120s rather than the 6550s my amps normally used. So to experiment I swapped the KT120s for the 6550s in my original Premier 12s and...there it was! That same effect, bass seemed bigger, deeper, a bit more controlled, the sense of soundstage space expanded, bigger sonic images. Going back between the 6550s and KT120 tubes, the 6550s produced a tight, precise, closer to "solid state" level of focus, bass punchy but less deep. The KT120s seemed to slightly de-focus the sound, I could hear instrumental sizes and voices expand, though with less delineated "edges" to the images, the bass warmer and deeper - I'd say that seemed maybe the most obvious apparent difference. I'd just gotten rid of a pair of subwoofers in my system and with the KT120s it sounded more like I had the subwoofers in the system again. (Not saying it actually added that much bass, but subjectively the effect was similar).
Still a novice with tube rolling I did some research on the KT120s and over and over the "reports/reviews" from people trying KT120s was "bigger soundstage" and most often "Wow! The bass! better/deeper/more bass."
So I found it fascinating that what I seemed to hear to my surprise matched what others reported as well.
Once again, given the anecdotal nature I'm not for a moment claiming I've shown anything at all about tube rolling that someone here should accept. Though the impressions reported above seem very convincing to me subjectively, I always hold out that it could be "rolling placebo" in Amirm's words. Though, despite the limited examples in Amirm's review, I do see even in this thread some talk about how tubes could in principle alter the sound, so I'm open minded on the issue at this point.
