Audio Research amp's retubing experiences

Hello I have to retube my ar ref 600. someone retubed ar amp's generally?
the amp has 6550 svetlana C and 6922 sovtek's. since we are speaking of a big (!) number of expensive number's I am asking which brand are to choose... someone suggest me telefunken nos goldpin, others amperex bugle boy or mullard nos....
for the powertubes someone suggest me to use kt88, instead of 6550...
some suggestion's
Thank you very much!!!
I recently re-tubed my 2 ARC Classic 120 monoblocks. I buy from the Parts Connexion, 16 6560c Svetlana`s, 20 tubes total for about a reasonable $450, (I requested and got matched quads).
I too was going to try KT88`s but at the last minute I found out you have to move a wire in each socket if you change to KT-88`s, something I can`t do.
This is my fourth set for these amps and I`m very satisfied with the Svetlanas, your situation with a ref 600 may be different,
Len W
I didn't like doing it, because it was expensive, but I worked through my dealer and re-tubed via ARC for my VT-100 MkIII. I'm glad I did. In the process, they found a bias adjustment problem, and did a minor repair that will prevent unpleasant occurences in the future. Also, the end result sounded as good as new. (I think tube-rolling is kind of interesting, but, having blown up several tube amps over the years--which I've found to be ugly experiences--I leave the amps to the pros. Pre-amps and phono-pre's are a different story...)

Just my two cents.
The most recommended tubes for the Audio Research amp are the 6550c SED. I retubed in the past Classic 60 with Svetlana very successfully. I will retube a pair of Classic 120 in closed future and i will use 6550c SED tubes.
I know the telefunken E88CC and ECC88, both work very well on Audio Research Preamp, but inside an amp like your pair of Ref600, to be honest i don't know. Be aware that the telefunken tubes are starting to be very expensive, no way to get a pair of E88CC fully tested for less than 200$
I don't think you can go wrong with the 6550 SEDs. There may (may) be a better NOS, but that can lead down a slippery slope that may not sound better with your ARC than the SEDs. I would look to Upscale Audio or the Tube Store for good matched sets. If you are still interested in KT88s, I would ask ARC for their opionion - my sense is their circuitry is optimized for 6550.
I retubed a VT200 with SED 6550's from a well known Canadian tube seller. One of the tubes shorted upon turn-on and this blew out a resistor and a few inches of circuit trace. My savings cost me $500 in shipping and repair (The 200 must go common carrier). What is the liability of buying a bad tube from another seller? They replace the tube. That doesn't come close to my costs. Also, pins on these replacement SED's were thinner than the ones on the ARC SED's, making a much looser contact. That may have been the problem, not sure. If you retube through ARC, it comes with a warranty. If you can test the tubes other than in your amp, then save the money and retube elsewhere, but make sure you are getting the thicker pins.
Dbarger, were your replacement SEDs in the Rew/White/Black Winged C box?
When I owned my Ref 600 Mk lll's I retubed with KT 88's which produced much sweeter midrange but at the expense of bottom end. Nonetheless, much better result than the 6550's provided by ARC
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!
Although the AR dealer here in Holland adviced to stick with the original Sovtek 6922 for my LS-2 pre I decided to play around with it, helped by a friend who graciously lend me two Philips tubes, a Gold Aero and a Sylvania. All sound different, so it's a matter of taste. I prefer a JJ I bought. It just shows you can 'tune' the AR to suit your taste and system.