hmmm...
This is a tough one...
I've checked out a few books on the subject.
Dan Torres' book was the best I thought. The "untimate tone series" didn't do much for me (only checked out the 1st one.)
I keep referring back to the Torres book. Looking back it has been the best one when it comes to simple coverage of what you want to know. It covers everything from power supplies, transformers, classes of operation, biasing, to layout.
THere are other books that are more "indpeth" but this one will teach you all you know to get started building an amp. If you want to know how tubes work, then read up from the "RCA tube manual" found in the manuals section os schematic Heaven