Update.
Oliver Archut suggested that I resolder the pins on the tube. This has worked so far. At least enough to use it. By this I mean that it’s still kinda microphonic, but only if I knock the mic. It doesn’t ring like it used to. Sound does not trigger the ringing any more. I only have this amount of experience with this one U47, so I don’t know if they in fact all are microphonic when knocked a little bit…? I am thinking that it could be it still has a “bad” filament, but that the soldering somehow changed the way the filament behaves? Maybe the heat from soldering altered it? Anyway, it’s usable now, and because of the fear of killing it, I still have not tried to really knock it.
By the way, this tube now lives in a copy that I built. The copy has an original K47 and an Oliver Archut BV8 with NOS lamination built in the Archut 47Kit. It has got “that” sound. The original 47 has now got the Andreas Grosser VF14EF, which is in my opinion a great substitute. The original VF14 does sound slightly more “exiting”, but so far I’ve decided to just keep the VF14EF in the 47. I’ve only really missed the “exiting” sound of the original when I’ve recorded soft singing vocals, but for that I can now use the one I built. As soon as you sing or play a little louder, there’s not really much difference between the two.
While it may sound strange to some, I don’t know if I’ll ever put the original tube back because now the 47 is a reliable and great sounding tool, “just as it was” with the original and besides, I don’t have to worry about a VF14 failure. Maybe a “new” original tube one day, I don't know, but for now I’m really happy with the way it is.