Audio Research CA50 + tube rolling

If your output tubes are still strong: Try some Amperex 7308s, like these:(http://www.upscaleaudio.com/Amperex-7308_p_100.html), in the driver positions first. If that provides what you consider an improvement(it's almost guaranteed to); buy some for the preamp inputs(they have to be graded very low-noise for that slot though). Mention what flavor of presentation you prefer(ie: warmer, tubey, Brit sound or more detailed and transparent) and further recommendations can be offered. Any of the better NOS tubes will open up your sound stage, provide better ambience recovery, and focus(depending on the rest of your system and room of course).

I think you'll find that the consensus on those Sovtek 6922's is that they are sturdy and reliable tubes available in production quantities (the reasons ARC uses them) that happen to sound 'harmonically bleached' and about as far from the sought-after sound of NOS tubes as you can get.
I don't have the CA50, but for what it's worth, my LS7 preamp and PH3 phono stage were both transformed when I replaced the stock Sovteks with a mix of Amperex Bugle Boy 6DJ8's and Amperex orange-label A-frame 6DJ8's. I've never sprung for the pricey 7308's or CCA's ($$$!), which I'll bet would be even better. But once I listened to the NOS tubes for a while and then put the Sovteks back in "just to see" - it was almost unlistenable - seriously. Output tubes might be a different story, but tube-rolling the input and driver tubes is a total breeze, and if you don't like what you hear, you can simply put the stock tubes back - no harm done.
Enjoy!

The driver tubes have to be matched and the voltage adjusted when they are changed. The procedure may be in the manual. I dont think you can just swap out the tubes.

If this is true then the design is wrong and arrogant !
I mean, one of the joys of owning tube equipment is to be able swap tubes every once in a while isn't it ?

p.s. is there anyone out there who actually owns the CA50 and tried tube rolling with it ?