This book provides in-depth technical analysis of valve circuit design and its rigorous application to the particular field of guitar amplifiers. It has a refreshing and very informative approach, worlds away from the technical treatises on hi-fi valve amps (excellent, but largely irrelevant to guitar amps) and the books that treat building guitar amps as a mystical art, largely lost to modern civilisations. If you want to understand how guitar amps really work, read it!
The only problem with the book is that, in the figures, the details drawn faint are so faint that it's possible to miss them altogether. Perhaps that will be put right in the next edition.