I'm going through this chapter by chapter. Since it's no longer published, I was lucky enough to discover pmillet.com and download it. It's over 1400 pages, so I just print out a chapter at a time. By far the most technical book I've ever delved into - I have to brush up on my algebra and re-learn all the calculus I've forgotten since college, (plus some continuing education courses on differential equations). But I can't recommend this enough for anyone who wants to grok vacuum tube circuits. I don't think I'll ever 'finish' it in my lifetime, but I will always be going back through it to refine my understanding and open up new caverns inside my brain.
This edition is smaller and less comprehensive than the 4th edition. In some ways this is actually better: this (3rd) edition focuses on triodes rather than pentodes for power amplification, and its smaller amount of material means it is easier to get a handle on than the behemoth 4th edition.
You could say that this edition represents the state of the art before WWII and the 4th edition, after.
This book will forever be on my "currently reading" shelf - it's over a thousand pages of electronics reference material and is known as the bible of vacuum-tube audio information.