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

I got in touch with Audio Research and this is what they said:

"Different brands of tubes can certainly change the sound so if you need a warmer sound you could try some alternative tubes. I don't have any specific suggestions as to brands or models but as long as you use the equivalent to the 6922/ E88CC tubes you won't hurt anything. 

Thanks,"

So I did some research and bought some tubes and yes, the tubes made a big difference.

The best so far is the Western Electric 2c51 (5670) with a 5670 to 6922 adapter. The sound is more warm and musical (to me) with this tube.  Another great one is the Mullard 10M 6922 which also sounded great but being new they should improve with some break in.  Amperex holland orange globe also sound great.  All much better than with the JJ. 

I am surprised how good the dac and  headphone amp are on the relatively inexpensive amp.