JADIS JA80 with 6550 or KT 88 or KT90 ?

I have nearly new pair of JA30’s with KT90's factory fitted. Are any changes or re-calibrations required when changing between KT90’s, KT88’s or 6550’s. Or is it a straight swap?

Bump this one back to the top, looking for an answer to valve inter changeability.

from Jadis via email:
"JA30 is an autobias amplifier, it does not need any adjustment when you change tubes.
Kind regards,
JADIS Service Commercial / Sales Department
Chemin du Pech
11800 VILLEDUBERT. FRANCE
www.jadis-electronics.com
Tel : + (33) 4.68.78.63.30
Fax : + (33) 4.68.78.85.15"

The KT88's just arrived, replaced the KT90's with the Elecrto KT88's and after only 10 minutes of listening, promptly placed them back in their boxes. I'd say the quality lost is near 50%. In fact had the original JOR came with these 88's I'd be one very un-happy camper.
Dumb me, doubting the french.
loss in all three fq's in the 88's.
hopefully my seller will take them back with some discount of course,.if not I;'ll put them up for sale here.
Paul

Paul, whenever you retube an amplifier, this happens.

Put the tubes back in, and let them run in for at least 25 hours. They'll open up. Trust me. It's called break in.

Now, I'm not the biggest fan of EH KT88 or 6550, and you may end up preferring the Ei KT90. But, whatever you use when you retube, even if they're Ei KT90, when you first power them up, they're going to be EXTREMELY constricted sounding, especially at the frequency extremes, and lacking in power big time.

Personally, I like the JJ tubes the best. But, interestingly enough, I have also arrived at the conclusion that the Chinese tubes being produced today are far better than anyone would expect. I would have never believed this if someone told me, but I've tried some small signal tubes recently that surpassed some extremely well regarded NOS varieties. But, even they needed a day or two to open up to the point where I was satisfied with them. For my money, I'm hoping I never have to buy another Russian tube.