Red:
Swampwalker's advice to review the info on AA at Joe's Tube Lore is good. I have found his information to be helpful to me. I am following his advice and am awaiting delivery of Amperex Holland Bugle Boys which he favors.
Specific to your search for info on 12AU7's, while you are on AA, search for postings on 12AU7's by Robert H. Several on AA seem to hold him in high regard as the resident 12AU7 guru.
Swampwalker's advice to review the info on AA at Joe's Tube Lore is good. I have found his information to be helpful to me. I am following his advice and am awaiting delivery of Amperex Holland Bugle Boys which he favors.
Specific to your search for info on 12AU7's, while you are on AA, search for postings on 12AU7's by Robert H. Several on AA seem to hold him in high regard as the resident 12AU7 guru.