Tube rolling signal tubes on Audio Research I/50

I don’t roll tubes on my ARC stuff, because the sound is crafted to be, well, that sound with those tubes (carefully tested to meet specs). Having said that, I look forward to hearing what you find, 

I did try NOS 6550 on my ARC preamp... the difference was very subtle... ever slightly more musical. But that is a power supply tube.

FWIW, IME 6922's (and 6dj8s) are not inherently a 'warm' tube. As 6922's and other tubes of that type go the JJ's are actually on the warm side of neutral and quiet. I use them in a tube headphone amp and a CD player for that reason. I used the JJ's in my ARC SP10 II and liked their tone, but they were driven too hard by the preamp and died very quickly (ARC used Sovtek tubes because they were rugged, not because of their neutrality I think.) Of new production 6922's I've only listened to EH's. They are rugged for sure, but I always found them a bit on the dull side. 

Look for dimpled disc getter 6dj8's/ECC88's from Mullard Mitchum (sp?) or Blackburn plants (by far the FATTEST sounding 6922 type that I am aware of) with a nod toward Blackburn.

These are later production tubes (late 60's into the very early 70's).

You need either one or a matched pair depending  on what the tubes function as.

DeKay