Hi, you have Mullard new production tubes. I have a CJ cav45 S2 and mine came with the same Mullard tubes.
I also have some Mullard xf2 Blackburn plant el34’s. The xf2’s are better but they should be at $200 each. What surprised me was how nice the new production tubes sound.
I don’t use the amp as much as I should but If I didn’t have the xf2’s I could be perfectly fine with the new production Mullard’s. The xf2’s give you a little more sparkle and air and little better bass. I hear kt77’s sound good I just I haven’t tried it.
I’m guessing yours came with 2 NOS RCA signal tubes and one new production 6922. That 6922 can really make the amp shine try some amprex, Valvo and others if you already haven’t, it’s only one tube. The Amprex brightens it up Valvo mellows the amp out more but keeps the highs. Good luck you have a very nice amp.