Here are some of my favorites.
The Art of Electronics, Paul Horowitz and Winfield Hill
The Electric Guitar Amplifier Handbook, Jack Darr
Solid State Guitar Amplifiers, Teemu Kyttala
The Circuit Designer's Companion, Tim Williams
RCA Receiving Tube Manual #17
Radiotron Designers Handbook #3
Inside the Vacuum Tube, John F. Rider
Electronics for Guitarists, Denton J. Dailey
Electron-Tube Circuits, Samuel Seely
Theory and Application of Electron Tubes, Herbert J. Reich
Basic Theory and Application of Electron Tubes, The Departments of The Army and The Air Force, February 1952
tubebooks.org - Vintage info from the age of vacuum tubes is a great re-source as well
I would recommend "Inside the Vacuum Tube," "RCA Receiving Tube Manual #17," "Electronics for Guitarists," and "The Electric Guitar Amplifier Handbook" as slightly less technical. The rest are pretty academic with lots of math.