It is always great to have online resources for technology books:
For books containing primarily tube data, like Sylvania, GE, and RCA tube manuals, see the tube data page.
Arranged by subject category, then alphabetically by title. Note that there is much overlap in the subjects (e.g., many “radio” books have a thorough treatment of vacuum tubes, and most general textbooks cover radio and vacuum tubes in some detail). Use (ctrl-f) in your browser to find a particular book or author…
On most books you click on the name of the title to download an introduction (the first few pages, usually the title through table of contents) This way you can see if you’re interested before downloading many megabytes of data.
General Electrical Engineering Books and Textbooks (pre-1964)
Audio (hi-fi, amplifiers, speakers…)
Radio (transmitters, receivers, design, repair…)
Vacuum Tube theory & circuit design
Test & Measurement (equipment, instructions…)
Passive components (transformers, capacitors…)
Other (transistors, tape recorders, odd stuff…)
I am interesting in learning more on Vacuum Tube theory and have found some of these online resources invaluable!