Obtaining detailed valve data used to be extremely difficult, and the author considered himself to be very fortunate in having a large collection of printed Mullard valve data sheets. Fortunately, there are now many excellent sources of scanned valve data sheets, and full manufacturers’ data sheets can now be found at various sites, but the definitive site has to be: http://tubedata.org.
Frank’s site is a service to the world, and the author would be lost without it.
Sadly, website addresses change rapidly (in terms of book lifetimes), but many valve vendors provide updated links to useful sites. Keep searching.
European Pro-Electron Valve Codes
The Pro-Electron system of valve codes gives significant information about a valve. ...