[Arran]

Chris:
B.T.H was the British subsidiary of the General Electric Company (in U.S and Canada not to be confused with G.E.C) so that would in part explain why they were manufacturing tubes for Ediswan, and why Ediswan was marketing them under the "Mazda" trade name. General Electric also developed both metal, and octal based tubes, which were introduced by RCA for 1936, so there is a tie in there as well. It's sort of an oddity of history that in Europe, and Britain, spray shield tubes were almost the norm, but metal tubes were the exception, I believe that Germany and the USSR were they only one that manufactured them on scale, the latter licensed from the U.S. Maybe Italy did as well, not certain, though they did use American type tubes in many of their sets, apparently Magneti Marelli got a license from American Bosch to produce Bosch sets in the late 1920s.
One company that used North American tube types almost exclusively was Kolster-Brandes, a K-B is one of the handful of British built sets I own, they were owned by Standard Telephone and Cables, which was a division of International Telephone and Telegraph. This makes it easy to find replacement tubes, as opposed to an HMV or a Cossor, where they used tubes/valves with their own system of numbering, sometimes with different pin outs. I also have a Bush DAC90A, and it uses rimlock tubes of the Phillips/Mullard pattern, not impossible to find thanks to Phillips being a major manufacturer in many countries, but unlike for the K.B I don't have boxes of spares like 6SK7s or 6V6s.
Regards
Arran