Audio Research amp's retubing experiences

the tubes in my 600 are svetlana C 6550. since they are very good tubes, I would try to change the 6922 from sovtek, what I know a good and rliable tub, but absolutely not camparable with nos telefunken etc. A technician said me the always first tubes makes the sound....
Now I am considering varous tubes brand's , since the price for 24 matched telefunken, about 100 Euro/one here in italy is not a joke. Some good ideas? someone tested Amperex BB, Philips, Siemes Mullard's?
The best dealer for tubes in the States?
Thaank you very much...

For NOS, I have had good luck with Vintage Tube Services and Brent Jesse.

Anyone tried the BLACK SABLE SEDs 6550C instead of the regular ones ?

Tube Depot carries them at a 100% permium.

I finally choosed to replace, for the first act, the little tubes inside, the12+12 sovtek 6922 with mullard military grade nos and telefunken nos for the input tubes.
The sound improvement is no less then dramatic... the amps are quite not same.
I am speechless.... I suggest to try the same to all arc owners!!!

I just purchased 12 of the reissued Tungsol 6550's for my CJ power amp and they sound very good top to bottom with a good sound stage. They replaced SED winged C 6550's, which replaced ElectroHarmonix 6550's. All of these brands produce quality sound, but I preferred the Tungsol's. If you need to save the $$$, try the EH, it's a good tube and they are reasonably priced. I've read that the cryoed version of the SED 6550C wasn't any better than the regular version. Don't know if it's true, but I wouldn't want to spend all of that money to find out that it was only hype! Good Luck!