Someone else had me start at www.sonicfrontiers.com They have 2 really awesome articles on the history of tubes on their site. These are great reading. After that, pick up a copy of N. Crowhurst's amp design book-he wrote several (usually on ebay). Finally, try www.tubesandmore.com-they have quite a few high quality books for sale. This is the route I took and it was great.
After that, pick up an old fisher, scott, pilot or similar tube integrated amp at a garage sale and play recklessly for a few months. Roll cheap tubes and clean it up. You can always resell these even if you trash them.
After that, pick up an old fisher, scott, pilot or similar tube integrated amp at a garage sale and play recklessly for a few months. Roll cheap tubes and clean it up. You can always resell these even if you trash them.