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.

Kevziek, the resistors smoked right at the moment when I started adjusting the bias. ARC just commented that the tubes are simply bad, I am not sure if it's true or not. I think Teslas draw too much voltage. The voltmeter went quite crazy. After my experience, I would not recommend JJ teslas for that amp and stick with the best vintages of 6922.

I own the VT100 MKII. With NOS 6H23 (type 3 6922) from Upscale audio, the VT100 MKII equals the MKIII in terms of slam, basss solidity and dynamics. However the MKII is more liquid and musical. The MKIII tends to be a little "dry" sounding. The VT100 MKIII reminds me of the older Classic series (60, 120) which were also hybrids. I disagree with Leonard: In my opinion, the VT100 MKII is the better amp for music enjoyment, although the VT100 MKIII may be "technically" better

You should not replace the input tubes without proper biasing. Biasing is tedious and difficult. Without proper adjustment, the output tubes will arc and blow the 1 and 100 ohm resistors (which are essentially fuses in the plate and grid circuits). In addition, the input tubes require tight tolerances and close matching.

Gmorris, thank you. Kevin from Uscale Audio recommended me the 6H23. I decided to let ARC to install input tubes. Just too much hassle to bias them by myself. I might experiment with EH KT-88 output tubes instead. I will decide when I get the amp back and evaluate the sound with new tubes.

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.