Is there a reference book for tube substitutions??

I have owned tube audio equipment for some time now, but have just started to get into the tube rolling game (funny thing; I have always experimented with NOS in my guitar amps but never my stereo). I am wondering if anyone knows of a good (but not too technical) reference book on tubes. I would love to find something that covers tube substitutions, history, and some technical background.

Thanks

Chris