can i change tubes

What does CJ say?

It should not be a problem just make sure it isn't biased to hot. The 6550 and KT-88 are almost interchangeable the sonic are quite different.
I personally found glory in the reissue Gold Lion KT-88s. Use a good dealer like Jim McShane a sponsor on AA tubes forum, he is careful about matching and screening the tubes for losers. They cost a pretty penny for a non NOS tube, don't be shocked, but they spank everything else in the amp I am using. (Jadis DA-60 )

Below is text I got from CJ's FAQ page.

Questions about Conrad-Johnson Vacuum-Tube Components:

Q. Can I replace a tube with a different tube type?
A. No. You should only use the tube type that is specified by conrad-johnson or an exact substitute. Using a different tube type can be expected to degrade performance and may damage the product.

I would call or email them anyway. I have VTL 300 Deluxe and changed out the 6550's with KT-88's recently. The reissue Gold Lions KT-88's are as good as everyone is writing.

Good luck

Not sure what has changed, but this is from a previous post of yours and members gave their thoughts/opinions :

have conrad johnson premiere 140 , can i remove the stock 6550,s and replace with my quad match set of genalex gold lion kt88
Pavpet (Threads | Answers)

05-25-08



Responses
05-25-08: Mingles
You shouldn't have any problem. They're interchangeable.

http://en.wikipedia.org/wiki/6550
Mingles (Threads | Answers)

05-25-08: Lapierre
Giddy up! Replace those fuses (Isoclean or HiFi Tuning) while your changing to the Genalex Gold Lions.

Spin the Yellowjackets.
Lapierre (System | Answers)

05-26-08: Fjn04
Check with CJ tomorrow to make sure. They seem married to
the 6550.
Fjn04 (Threads | Answers)

05-27-08: Cyclonicman
When I checked with CJ regarding my CJ power amp, I was told that if I used KT88's instead of the 6550's, biasing the amp would be a problem.
Cyclonicman (Threads | Answers)