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There were only a handful of actual tube manufacturers back in the day. Many brand names on antique tubes are just a stamp on the tubes mentioned above. If you find any tube with a major US manufacturer stamped on it (Like Zenith Philco GE RCA) it's probably made by Sylvania RCA Tung-Sol [New production made in Russia IIRC] National Union, Cunningham, or maybe a couple of others. I primarily deal with radio tubes (as mentioned) but have found the new-production foreign tubes to have a substantially shorter life over old 'Merican made tubes.