[Arran]

     Thanks Greg and Arran.   I do have a 1629, but I don't think it is very bright. I will try it .
 I checked out some 6U5G tubes and'' BOY'' are they expensive.

Dan;
  The 6U5s you are probably running into are of the more common six pin based variety, the prices on those are all over the map from somewhat reasonably priced good used ones to idiotic "pie in the sky" prices for NOS ones. The 1629s are usually much cheaper, but you have to watch it with those as well as some sellers really just pull prices ouit of thin air. How dim is the 6X6 anyhow? Can you see any green in it at all in a moderately lit room?
  Here is a page with some eye tube information, not all, but it might give you a few leads:

http://www.magiceyetubes.com/

 
Regards
Arran