useful links
www.ampbooks.com - Companion website to the Amp Book series from author Richard Kuehnel. Very useful online calculators to aid in amplifier design.
www.robrobinette.com - A great website with lots of tube amp explanations and useful information.
www.schems.com - A basic, but great website with tons of schematics, books, and resource manuals for guitar tube amplifiers, pedals, and more.