preamp tubes

[noarin]

Can anybody give me a rundown on the difference between the most used preamp tubes? or post a link to a site where I can find information... I'm aiming at the differences between e.g. a 12ax7 or 12au7 tube, etc.

Thanks in advance.. sorry if it has been asked already!

 

[Wild Hades]

12AX7s have a "mu" (amplification factor) around 100, so they have higher gain.
12AU7s have a "mu" around 20, so, a lot less gain.
That's why hi-gain amps use 12AX7s, usually... they operates at different voltage/current settings btw...

 

[Metaltastic]

http://thetubestore.com/gainfactor.html