http://www.bottlehead.com/smf/index.php?topic=3453.0 Quite a bit of comparison here too. Hope it's useful.
The RCA 6AS7 is right at the bottom pertaining to the Crack amp. Not sure if the findings are true for the 339 as well :(
BTW, any tube rolling guide for the 6922?
Edited by snip3r77 - 3/22/13 at 9:30pm