Books on Tube Rolling

I would like to know if some one could recommend a book on tube rolling. What is using a 12au7 vs.a 12at7? A book that would tell you options for a given tube etc. etc. etc.
You need a tube substitution manual. SAMs made them as did others. You
should be able to find one at Antique Electronic Supply or ebay. You might
also want to pick up an RCA Receiving Tube Manual so that you can see
the actual characteristics of tubes.
This is not quite what you asked for, but it's been pretty much the de facto source for tube rollers:

Joe's Tube Lore
Thanks for the info you two.
Crowhurst is legendary with amp builders. I've read this several times.