Call Andy at "Vintage Tube Services",or Jim McShane. Both of these guys are the real deal when it comes to recommending and supplying good tubes that are quiet and tested to the max.
Both posts here are excellent ideas. Andy @ Vintage Tubes, and Joe's tube lore...
I'm wondering though, why move off of the 12AX 7 TO BEGIN WITH?
There are a lot of these types of tubes around which should meet your needs. Amperex Bugle boy 12AX7's ought to fit very well. Quite extended, dynamic, and very clean & clear window to the music. I use a combo of these and RCA 12AT7s in my preamp.
I would definitely try a 5751(GE black plate or Tung Sol))which has a gain factor of 70, while the 12AX7 is rated at 100, so you would have a 30% gain reduction. I think the 12AT7 mentioned by Yogiboy and rated at 60 might be too drastic a reduction at 40% gain reduction. I think this is especially true if the Aronov has a phono stage.
Does anyone have any updates regarding the Sovtek 5751 tubes? Has anyone used it with their amps and care to share their thoughts? I enjoy 5751 type tubes (currently JJ 5751, previously NOS GE black plate 5751) in my Jolida amp. I was thinking about trying something different with these Sovteks.
Thanks and advise when you can.