Big "Fat" bottle 6CA7's in Mark IIB?

[MK IIB]

Hi folks.
I've got a pair of Sylvania big bottle 6CA7's and I'm wondering what the difference in tone/feel would be with these in a Mark IIB?
The Boogie has a bias pot installed and these were actually in there when I got it but I didn't actually hear what they sounded like as I put the amp in to have it returned to stock with Current Production Mesa 6L6's.
These haven't been used a lot and as they are NOS I'm curious how diffrent they would sound?

 

[Boogiebabies]

The impedance on the IIB output transformer is designed for 6L6 power tubes. I'm sure that it can handle 6CA7's but I don't think it's a good idea. Maybe a difference in the top end, but not worth it.

 

[MK IIB]

Thanks BB.
Could running these in the Mark IIb have caused any damage to the OT where it would still function but affect the sound?
This amp just isn't sounding right at all.It's been serviced,recapped,retubed but sounds thin and is lacking in gain.I've tried new tubes etc but it just doesn't sound as it should?