I have an old (original) copy of this manual. It is of considerable value
when any question or point of curiosity about a tube comes up.
As with any other reference book, it has notable omissions
and inconveniences that can occasionally frustrate,
but overall it is good enough for most purposes.
For me, the least usable feature of this publication is the substitution guide.
Better ones are easy to find (H.W. Sams, for example).
If you work with tubes, you should have this book
on or near your bench at all times.