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
@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.
Jfreck - I've tried and permutated with most of the acclaimed tubes out there and yes you win some but lose some.... After one big big cycle, I landed back to the stock tubes.... Quite a joke right?
Hi, not sure it's a joke...just tells me the stock tubes are very well matched to the the circuit in the Nagra...

The jokes on us maybe for spending more money on other tubes :-)