Power Amp Tubes

[Vlover]

Is there a GOOD internet source on the difference between (sound of) Power Amp Tubes? Like the difference between EL34's, 6L6's and KT-88's etc....

[Dreamland_Rebel]

www.thetubestore.com is a good place to start.

[Spivonious]

Building on this thread a bit, is there a good site for differences between the same tubes? I'm always hearing how these 12AX7s are bright, these other 12AX7s are dark, etc. What causes these tonal differences?