Audio Research amp's retubing experiences

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.