Bcgator
I've got a VSi55, and would like some tube recommendations...rather than start a whole new thread, let's resurrect this thread after an 8 year hibernation...
Lots has happened since 2006...KT120s have been introduced to the mix (and fully compatible with the VSi55), and the KT150 (about which ARC is still mum regarding compatibility, and I have followed the other KT150 threads here but didn't want to hijack them), and I think the introduction of the reissue Gold Lion KT88s is a relatively new thing as well.
Unless that ARC amp was designed for KT-120s I would just plug and play. Call ARC and verify the new design KT-120 is compatible without modifications.
Hifigeek1
If you can still find winged C 6550's don't use them. The last of the production was not reliable. Apparently the plant burned down and are no longer available.
The plant did get destroyed but there are some of us with a supply of Wing C tubes from years ago. I bought about 200 of them several years ago and still have 55 or 57 of them matched and new in box,
The Wing C is the best sounding modern KT-88/6550 there was (in my opinion).