The Dutch Phillips company owned several tube makers including Amperex, Mullard, Siemens and Valvo. Tubes were frequently made by one manufacturer and labelled for another.
Tubes were etched, usually near the bottom of the glass, with a code that designated where and when the tube was made. Google Phillips Tube Codes and you can find a pdf file with information about all the various tube codes.
Tubes were etched, usually near the bottom of the glass, with a code that designated where and when the tube was made. Google Phillips Tube Codes and you can find a pdf file with information about all the various tube codes.