ARC Ref and tube rolling

I am a newbie when it comes to tube equipment. I have had the ARC Ref 3, Ref 110, and Ref CD7 for a couple of years and they are my first set of tube components. Has anyone experimented with tube rolling with any of these units (what are some of the favorite flavors of the 6550 output tubes in the Ref 110 - which I guess is the obvious place to tube roll - relative to the stock tubes that come from Audio Research)? Also, are there any issues one ought to look out for if one were to experiment with tube rolling with ARC components (voided warranties, ARC gear not self biasing, etc...)? Thx for help in advance.
I would call Leonard at Audio Research and ask him. Personally I would confine my tube rolling to the small signal tubes in the preamp and or cd player.
I did swap the 4 6h30p's for 6h30DR's supplied by the tubestore and liked it very much. More open, detailed well worthwhile though costly now. Power Tubes were better as standard, i tried a Tung-sol 6550 and it seemed a bit bloated, so swapped back, and preferred that.
Sorry, neglected to say that was in the Ref 3...
Thx both. Appreciate the feeback.
I have tried the NOS 6550 TungSol Black Plate from the 50's (not the new TungSol reissue tubes, which are crap IMO)in my Ref 3 and it was a major upgrade. I cannot recommend it highly enough. I had written abot that in detail in another thread. My syetem at the time was Ref 3, Ref 110 and Ref 7.
Thx Elberoth2. Did you try the NOS 6550 Tungsols in the output stage of the Ref 110? I guess having never done this before, I am at a loss as to where to start in terms of which tubes to replace and with what and how that is likely to change the "voicing" of my system. By the way, just to fill out the picture, my ARC components drive Thiel 2.4s with Nordost Heimdall cabling and Shunyata Hydra 8 handling power conditioning. I am interested in experimenting with tube rolling to see if I can get a bit more bass out of the Thiels and to see if I can introduce a touch of warmth (not too much) across the frequency spectrum.

BTW Elberoth2, you mention you used to have my ARC components (which is what is still listed in your Systems link). I am wondering what you changed to - just curious. And, beautiful listening room set up - very nicely done.

Finally, i looked through your threads and couldn't find the description of your tube rolling experience with the ARC components. Would you mind posting a link of the thread where you discussed this? Thx very much.
Cmalak - unfortunately, I did not have a chance to try NOS 6550 TungSol Black Plate in the Ref 110. Those tubes are very hard to find, and are VERY expensive. Last time I checked, Tube Store was asking $500 - each !

8 x $500 = $4000. That is way more than I'm willing to spend on an octet of tubes :-)

Ref 3 is another story, as you only need need one tube. I have discussed it here:

Hope this helps.
Thx Elberoth2. I just read the entire thread on tube rolling in the Ref 3 that you posted above. Very helpful to read through different folks' experience.