Aussiedrummer, "I think I will try the KT88 valves as Bob seems to think the amp will be fine with them. He does not see any reason why we can not use them."
Trelja, "I have my own opinion on the matter, but suggest you contact Jadis if you are that interested in using KT88."
Since it seems you are headed in that direction, I'll come out and say that my feeling is the same as Bob's. Still, my opinion is that while the bigger tubes will provide more slam, and that may be exactly what appeals to you (and should be really the only consideration), the right EL34 tubes will let the amp shine in a way the larger tubes cannot.
Finally, working off the presumption that your Orchestra is new, apart from moving to the Shuguang 12AX7B immediately, as there should be no delay in that, you may want to give yourself some time with the Jadis before you change anything else. For one, this is your first tube amp, and from what I see, it sometimes takes people a bit of time to acclimate themselves to the different type of sound. But, more importantly, when I got my first JOR, though I was warned to turn it on and just let it go for a full weekend of playing, and even at that, I'd be cursing the gentleman who represented the line, it literally sounded horrible. I was filled with a tremendous amount of buyer's regret. Slowly, but surely, the amp opened up and revealed itself, but it took a long time. I've never owned a component that took longer to break-in, I was still hearing recognizable improvement even after six weeks of daily playing. Along the way, what was once an incredibly constricted, thin, bright, and harsh sound extended at both the frequency extremes, and noticeably relaxed. After about three months, I noticed no more improvement, and then made what was a very large improvement, an all silver power cord. In my experience, most power cords to not make the type of difference so many ascribe to them, but this particular one on the JOR yielded an undeniable improvement. And, when I sold the unit to Denis, in moving from the Ei KT90 to JJ E34L (I also tried JJ KT88 at that time), the improvement was extraordinary.
Continued best of luck with the new baby!
