Electronics books that are specific to audio are everywhere but good ones can be hard to find. If you can find it, the bible of all tube electronics books is the classic "Radiotron Designer's Handbook", which is an enormous book with more than you'll ever retain, but a great reference nevertheless.
My current favorite tube books are Morgan Jones'
"Valve Amplifiers" and the newer
"Building Valve Amplifiers". Although mostly tailored to HIFI amplifiers, preamplifiers, phono preamplifiers, power supplies, etc., many of the principles are the same when applied to instrument amplifiers. He covers Thévenin, a little Kirchoff, etc. This guy was a BBC engineer for years and knows an awful lot, and unlike so many other electronics "experts", he teaches simply and effectively without sounding like an arrogant fuckwad.
For books specifically about tube and hybrid instrument amplifiers, PA systems, etc. I would suggest Kevin O'Conner's
books. Some of the first tube things I built were projects from the "Tonnes of Tone" book, including an 8 watt guitar amp, power supply, reverb unit, etc. There is some theory in there, but mostly it is analysis of existing designs (Fender amps, etc.) and ideas for improving them.
Good luck...