I would start here:
http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html#12AX7
This will give you a good idea of what to try. This is considered the de facto piece for tube rolling.
http://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html#12AX7
This will give you a good idea of what to try. This is considered the de facto piece for tube rolling.