I want to try a new set of power tubes in my Rogue ST100 power amp. This amp sounds too solid state for a tube amp. Recommend a power tube other than the stock KT120 than will give me more of a lush tube sound. I need four so please keep it reasonable in cost.
I have a Rogue Stereo 90 which is a very similar amp.
First off, if you are using the Tung Sol KT120, I think that tube is very dry and solid state sounding in my Stereo 90 and definitely contributing to your issue. You have several different ways to go. If you want to stick with KT88/KT120 I recommend the Psvane grey glass KT88 or Treasure black glass KT88, these have much more air up top and bloom in the middle than the Tung Sols. For less money, the Penta Labs KT88SC (also marketed as the Preferred Series by thetubestore.com) is also a good sounding tube in the Rogue.
If you can afford to loose some power, a 6L6gc can sound great, the Russian 6P3S-E is very good, Tung Sol 6L6gc-str or Tung Sol 6L6-G or any RCA or GE 6L6gc.
Vintage Mullard EL34 are very tubey sounding in my Rogue. KT66 can sound very good but I don't think that is the sound you are looking for.
Up front, vintage Mullard 12ax7s are very tubey sounding, or try a US 5751 blackplate. I would definitely go vintage for the 12ax7 spot, any RCA, GE, Sylvania, Raytheon or European tube from the 1950s or 1960s will smoke the stock tubes IMO. My personal favorite 12ax7 in my Rogue is the RCA black plate square getter. The 12au7s are driver tubes, maybe a vintage Mullard or Amperex in that spot. My Stereo 90 uses 6SN7s as drivers so I can't help you there.
I prefer using my Stereo 90 with the 4 ohm taps, bass is much better. If you can afford to give up power, Triode sounds better than Ultralinear IMO.
The Rogues are great amps enjoy!