With appropriate respect for the points made by the various reviewers of this book who gave it an average or below rating, I believe the complaints of those individuals are addressed if one views this volume as the companion to Mr. Jones' "Valve Amplifiers" volume, ISBN 0-7506-5694-8
Together, these two works provide a solid grounding in much of the necessary information necessary to grow one's ability to grasp what is happening inside a valve amplifier. In particular, his empirical work on valve performance and design features which aid or degrade such performance, and his firm grasp of what does and does not affect the tone of the amplifier, are both areas which the more traditional texts simply do not address. It seems to me that when one possesses a firm command of that knowledge one may then move forward, both with classic designs and (one would hope) new and original ideas in valve application.
Of course, if valve amplifier beginners wish to begin with monkey-see, monkey-do designs, there is a wealth of free information on the internet to that end. Such practice is valuable experience...but this is not what Morgan Jones' two volumes are primarily designed to do.
I post this review mostly to remind folks that it is the Morgan Joneses of the world who are both bold enough to publish, and who have the necessary technical acumen, and who have actually done the work of supporting research to validate their published material. Without folks like Jones, the modern valve amplifier landscape devolves into tube rolling, snobbery and myth...a death sentence to the valve art, IMO.
I never cease to be amazed at the number of folks who will spend over five hundred dollars for an NOS GZ34 rectifier because it has the Mullard label on it. More often than not, those same folks cannot articulate even the most basic principles behind good power supply design and its effect on amplifier performance. Yet, those same individuals balk and spending forty dollars on a book which could easily clear that issue up for them, to the immense benefit of the performance of their designs.
In conclusion, I find both of Jones' volumes mentioned herein to be valuable assets, even as I recognize they do not claim to be the end all and be all of valve amplifier design and construction. I applaud him for his work in this area. Rather than being overly critical or myopic about flaws in Jones's book, it might be more beneficial to skip this month's tube rolling expenditure for yet another pair of 12AU7 black plate NOS whatever. Instead, spend that money and help support Morgan Jones and others like him who are still publishing valve related material of sufficient robustness as to reasonably warrant ownership.
As an aside, I would agree with Frank Elliot's point that the Mullard publication, along with Rider's "Inside the Vacuum Tube" are critical pieces to the equation as well, and I would commend them to the valve enthusiast. Good luck finding the Rider volume - the current price is hovering around a hundred bucks, and they are in very short supply. The Mullard publication is, however, available for a very reasonable price on Amazon.