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 ($$$!), which I'll bet would be even better. But once I listened to the NOS tubes for a while and then put the Sovteks back in "just to see" - it was almost unlistenable - seriously. Output tubes might be a different story, but tube-rolling the input and driver tubes is a total breeze, and if you don't like what you hear, you can simply put the stock tubes back - no harm done.
Enjoy!
I don't have the CA50, but for what it's worth, my LS7 preamp and PH3 phono stage were both transformed when I replaced the stock Sovteks with a mix of Amperex Bugle Boy 6DJ8's and Amperex orange-label A-frame 6DJ8's. I've never sprung for the pricey 7308's or CCA's ($$$!), 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!