Again, I'm no tube expert, but tubes come in many different designs and built qualities from many different companies. Cost is only a very rough guide to quality, but different circuit designs dictate which tubes can be used. Tube rolling, swapping out one set of tubes for another usually changes the sound of the preamp, buffer, or power amp. Perhaps someone can recommend a tube handbook that explains the differences in basic tube circuits and why certain tubes are used in them. In my experience tube rolling is most effective in power amp output circuits.
Dabbled in tubes as always sought true tube magic - palpability (image density, touchable, tangible) but only found it an integrated amp that unfortunately output was too limited for my use and also had tons of bass flabbiness (was designed to complement high efficiency, bass weak speakers - this was a classic pairing 60 years ago). Never wanted to add colorations from source or amplification (speakers unavoidably have enough).
Heard no advantage of tubes in well regarded DAC and preamp (rolled to high end/recommended tubes from stock in both and they both had solid state options). Also had a Stereophile Class A recommended integrated that I rolled half a dozen sets of output tubes in and out of, which did provide a different sound each time. EL34 tubes made everything sound warm; the KT 66, 88, and 120 all sounded similar to my 10 year old class D mono-blocks; KT 77 sounded a bit better; 6550 sounded the best, but still only slightly better than those mono-blocks that were much cheaper to buy/operate and easier to live with. BTW my tiny, modern 70 watt Temple Audio mono-blocks sound much better than either.
