If it uses an EL34 then you can use a 6CA7 and probably a KT77. The only new production 6CA7 that is well recieved is the Electro Harmonix "Fat Bottle". I use this tube myself and it works remarkably well in my Opera Consonance Cyber 800 Monoblocks. The sound is big full extended treble with excellent bass or more simply a very forward sounding tube.
JJ is coming out with their own Fat Bottle version but the reviews are not in yet.
Yes you can use the Shuagang Treasure, but even though people seem to like them they are very expensive and I have a hard time equating a Shu with a truly premium product. The Gold Lion Reissues on the other hand are really good. I use the KT-88s in another set up and can't say enough good things about them. The KT 77 is supposed to be a superb tube.
No you don't have to change out both the 12AX7s and the 12AU7s at the same time. If you search there are many threads arguing the merits of both tubes.
For new production, the best bang for the buck IMHO, is the Tung Sol reissue 12AX7.
I still don't know of any newly made 12AU7s that come close to the old stock tubes sorry about that. I think Gold Lion makes one that might be good again. Then there is Psvane a black bottle tube from China which like the Treasure is very expensive for non NOS. I don't know if it actually OEM by Shuguang or not - could be another manufacturer like Full Music.
