advice for retubing of Jadis JA80

Hi:Rcp, Thanks for your vaulable opinion.
My JA80 is an early 90's(~1990-1991) production. I bought it from a friend and was told that it has only been used for a short period of time.(less than 200 hours), The power tube that came with it is a stock tube(GE 6CA7), if i'm not wrong.
I listen more on classical, piano, vocal and jazz.
I'm thinking to change the power tube in order to find the best sonic to suit my taste.
For NOS power tube is very expensive now, so that i would think of getting a current porduct to subsititue with it.
If i consider to get other power tube, do i need to rebias?
Samscs

I had a pair of that vintage. They came stock with GE 6550s at the time, which were serviceable but nothing special, and the worst of the types you could use in the amps (unless you scored some Tung Sols). Your tubes were probably substituted by your friend. I can't speak to modern tubes, I was not that impressed with them, particularly their longevity, so I gave up on them after a short try.

You do not need to rebias the amps if you change tubes, they are self-biasing.

I would try KT88s first, then EL34s, in your amps. For large scale classical you'll probably want the extra power and bass of the KT88s, for smaller scale material without deep bass the EL34s might be the ticket. 6550s will give better bass control, but I find most of them to lose the midrange magic that you pay for in a Jadis. Exception to that is NOS Tung Sol 6550s, which sound quite close to the KT88s. Perhaps some modern tubes would suffice for the start for you to see what you like, but I note that ultimately NOS pay for themselves in their longevity, as well as their great sound.

Defintiely go for cryoed tubes. tubemandotcom sells them