I found "Inside Tube Amps" by Dan Torres much more informative as far as actually working on amps. The paperback is out of print, but there's the link to the kindle version. It has detailed examples of mostly Fender, then Marshall and some Vox circuits.
You should check this book out:
​
It's weirdly edited but really informative.
You should check this book out: https://www.amazon.com/Inside-Tube-Amps-Modification-Amplifiers-ebook/dp/B01M3PQR5M/ref=sr_1_3?crid=3QYSDT54HSISA&dchild=1&keywords=inside+tube+amps+dan+torres&qid=1619138853&sprefix=inside+tube+%2Caps%2C224&sr=8-3
​
It's weirdly edited (self published (I think) in the 90's), but super informative. Mostly deals with old Fenders, some Marshall, some Traynor. It's cool cuz it shows the schematic and the actual layout. You could print out pages from kindle to get a hard-copy.