This site shows you different
construction types of ECC81, ECC82, ECC83, E88CC – EF86 - EL34, EL84 - GZ34 and other
audio tubes made by Valvo, Telefunken, Siemens, Amperex, Mullard, Philips (regarding their code as xf2 and their getter ...) a.s.o. Also
information about German Tube Hifi from the 60s as Klangfilm, Sennheiser, Telefunken
Nordmende and many more.