The Wauwatosa Tube Factory website,
http://wtfamps.com/welcome/, has a great series of posts on tube amp design and components. Topics covered include different methods of biasing tubes (and what bias is and why it's necessary), series versus parafeed use of output transformers, the use of constant current sources (CCS), and a bunch of other helpful stuff.
The basic math equations are covered, but the focus is on explaining what things do and why they're used/needed, and the different ways of meeting the operational requirements for getting amplified sound from output tubes -- all in everyday language. I've found it very helpful.
Just a heads up: the website author's sense of humor might strike some as a bit off-kilter.
cheers,
Derek
