best tubes for VTL,5.5 preamp.

just purchased a VTL.preamp used,this is my first tube audio equipment,much better than my,CJ PFR,ss preamp,VTL,sound little thin like fuller sound,anybody,knows,what tubes will give me the sound im looking for, thanks for the help;
Hi---I'm using a VTL 2.5 preamp with a pair of NOS RCA 5814 triple-mica 12au7 gives me a full but still detailed sound with a bit of warmth, I love them. What tubes do you have in your VTL 5.5 now?
I don't know the tube complement, if you post it I can tell you a few potential warm tubes to try.
I am currently using New Sensor Mullard 12AX7 in the line stage of my 5.5. These are nice and warm sounding. The New Sensor Tung Sol 12AX7 sounded good as well. These are my favorite new production 12AX7s. If you want to go NOS I really loved the American Tung Sol 12AX7s. The midrange was nice and warm and they had good weight and articulation in the Low end and a nice sparkle on the top. I also liked RCA grey plate 12AX7s.

Does your 5.5 use 12AT7 in the Line stage? If so I would recomend Sylvania 6201 Gold Brand or Mullard CV4024.

I have a ver.1 5.5 that uses 6350 and the only ones of those I have tried are Sylvania.

After trying several NOS tubes, I find the Amperex Bugleboy 12AX7 and Telefunken/Mullard 12AT7 tubes the best combination. Try it.

Hello -
Probably a stupid questiond
How can you tell what Version the 5.5 is and what the actual changes were? The VTL website does not seem to have that information and VTL has not responded to my question as of yet.
The unit # does not change( i.e. how ARC does with MKII or giong from say a LS16 MKII to an LS17).
Just curious because I will be looking to upgrade from my quicksilver in a few months and the 5.5 is on the short list.

Thanks in advance.
I have the MKII and it has the plastic remote instead of the metal one. Don't know when the switch was made, but I don't think any the of MKI had plastic remotes. So, if your remote is plastic, it should be an MKII. If metal you may have to call VTL with the s/n.