Tube kit for Nagra PL-L?


Nagra recommends that users purchase a "tube kit" from them as tube replacement. This at a price of a couple hundreds of $. What is so special about these tubes? Aren't these Sovtek tubes that are easily available off the shelves?

Any one made any comparison with these tubes?
shsohis
Some good tube dealers also burn in their tubes then test them above and beyond the manufacturers testing. Jim McShane is one such dealer. You can find him over on Audio Asylum or a simple search. I sure there are others do you know which tubes are involved?
I've had a tube get noisy on my PL-L, I've order the tube kit b/c of the comments above on testing/specs/matching Nagra does.

On the side, I have tried a few other 12ax7's (The TJ Full Music 12ax7's are pretty nice-more detail/bottom end...brings the image forward somewhat). You do get a gain here or there, but seem to loose something here or there also. The stock tubes seem to be just about perfectly balanced on all parameters.

I think the Nagra tube kit is about $250. So if you buy a few 12ax7's doesn't take long to burn through $250 in NOS tubes...and be underwater in comparison...

Let us know what you decide...
@Mcintech: Are the tubes the same in either kit? You just don't get all the ancillary "bling", in which I have no interest anyway.
Exact same tubes without the accessories. Contact Nancy at Nagra USA; (615) 451-4168. She'll have to order them, I think.