12 ax7 gain characteristics

[jestaudio]

Getting curious about the interaction between gain and viltage in a 12ax7(or any other similar tube) there is loads of information but very little that makes sense without loads of math, can someone point me to a article or explain in simple terms suited for dummys

[Colossal]

Blencowe, Chapter 1!
http://valvewizard1.webs.com/Common_Gain_Stage.pdf