Over 1Gb of vacuum tube books for free!
Here is a great collection of over 30 books on vacuum tubes, amplifiers and related electronics, all free just for the download time. It is over 1Gb of tube amp data! A great collection.
These books are old (uh, vintage) and the copyrights have expired and were not renewed, so I feel okay about linking to them especially since the page owner has contact info posted in case any of them are in violation.