[Maarten]

First thing I thought of as well. Prtty sure it just means 'mains'.

Something else: I don't think EAA91 and EB91 were the same valve, they had a slightly different envelope, but I don't know whether that's significant (industrial range, copy of US valve, etc).

Another thing is the industrial range. I think the French used different colours of chalc for printing on the valve, depending in which range it was.

Also, Philips might have had an alternate (factory internal) definition for industrial range, in which most 7 pin valves (including special quality and CV derivatives of the xxx91 etc. series) are just ordinary receiving valves and the industrial range only consists of special valves (thyratrons, transmitting valves, etc.). This is suggested by the documentation on the different factory coding systems (the 2 lines of small characters at the bottom).