ARC VT-100MKII to MKIII, upgrade worth the cost?

Gvatchna, I'm glad I read your response. I was going to try the JJ Tesla 6922. Did ARC comment on whether the electrical characteristics of the JJ are that different from the Sovetek? Did you actually adjust the input bias controls? I know how to do this after an intensive learning curve, but I would not recommend this procedure to anyone unless they are used to working on electronics, and, in addition, have a lot of patience and are willing to learn a number of things in the process.

I briefly had EH KT-88's in my VT-100 Mk II. I didn't find them nearly as good as the Svetlana KT-88s. However, I did not play these tubes more than a few hours. I guess it may be possible that these tubes need burn-in to know their true sonics. With Svet KT-88's, I never found burn-in to make more than a minor improvement in sonics, so I can't say I'm convinced that power tubes require any burn-in.