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Power tube selection, types and brands, make a big difference in sound, especially the types, i.e. KT88 vs LL34 and all varients.. For the small tubes the tubes that make the biggest difference is the center two tubes.
But it all depends on what you are hearing now and what you want to hear, tht is you need to have a sonic goal in mind before you start rolling tubes.
jb, Here is a link to a review that discusses tube functions in a Dialogue Premium preamp and some of the comments made by the reviewer, Dick Olsher, who is a respected reviewer. I think the functions would be the same in your integrated:
"There are two gain stages and a cathode follower output stage per channel. Looking at the 12AU7 tube array on the top deck, the two inner tubes comprise the first gain stage for each channel, the next two 12AU7’s over are the second gain stage, and the outer tubes are the cathode followers. Use of a cathode follower results in an exceptionally low output impedance of 256 Ohm, meaning that the PDP should be able to drive long cable runs with no problems whatsoever. SCR (France) tinfoil capacitors and Takman (Japan) audiophile-grade resistors are used in critical circuit locations.
"Out of the box, the PDP did not editorialize, being tonally neutral and faithful to the recording. The stock Chinese 12AU7 tube complement is quite good and I did not feel compelled to roll in vintage types. More out of curiosity, and in order to obtain a complete sonic picture, I first substituted for the first voltage stage and later also for the second voltage stage. I started off with a Mullard long plate ECC82 for the first gain stage, and later experimented with CBS 5814A for the first two voltage gain stages. It became clear that the stock tubes are all business. By contrast, the Mullard delivered a bit more sex appeal: a richer midrange and greater textural finesse. The CBS 5814A went further down the road toward a lush tonality, being even more velvety and dynamic. And to be honest, that’s a sound that’s easy to fall in love with. Let me emphasize that the stock tube complement is plenty good. But if you’re interested in improving the sound further, especially in the areas of tonal color saturation and microdynamics, then by all means explore vintage 12AU7 options such as the CBS 5814A and Mullard ECC82 long plate. And there are probably many other interesting options – that’s the fun of tube rolling."
tomcy6 again: I do not think the cathode follower has the impact on sound that the gain stage tubes do. I would put the stock tubes back in the 2 and 3 positions and start with your expensive tubes in the 1 (innermost) position. Get used to the sound and then experiment with tube changes in the 2 position. If the NOS tubes don’t make a difference in the 2 position leave the stock tubes in. The important thing is what you hear, not theory.
Finally, the stock tubes will probably be good for the 3 position. You can experiment if you want to though.
Regarding the Mullard longplates the reviewer uses in the 1 position, your Mullards have a similar sound but the longplates may be a little warmer and richer, at a higher cost of course. I think your tubes are a better value and will work as well as the longplates, especially since you can use them in both the 1 and 2 positions.
The description of the effects of the NOS tubes in the review are why we use tubes in the first place, so I think you’re doing the right thing by going NOS. If you want clean and lean sound, stick with solid state. Get your preamp tubes settled, since you already have them, and then work on the power tubes.
In my tube power amp I use a combo of new Gold Lion 12AX7s and NOS Mullard 6201s (12AT7s) from Uncle Kevin. I think the current version Gold Lions are great (I like the KT88s also), and I like the Mullards because they flash when you turn the amp on. It seems I may have a low threshold of entertainment.