Just uploaded a new version of the Radiotron 4 PDF to the Google Docs section of the GroupDIY Gmail account.
This version is fully unlocked and has no printing/copying/extraction/commenting/etc. restrictions.
But more importantly, I ran OCR on the full document so that you can search, select, and copy text.
I also uploaded a few other old tube books with full OCR. Inside the Vacuum Tube - John F. Rider 1945
Principles of Electron Tubes - Herbet J. Reich 1941
Electron Tube Design - RCA 1962