> Sounds like something is faulty in there and it needs fixing rather than a big conversion job.
It looks a little like a 1940s US radio inside. And after 60 years, these all need new power filter caps. And of course it will hum with the covers off: time to figure out what shorts when the cover is on.
While having the AC supply in the mike body sounds like a dumb idea, this was not a cheap mike and I'm sure it didn't hum (much) when working right.
The electronics are likely fixable, and probably simple.
The capsule could be like-new, or useless.
If you think the "looks" are worth $850+, go ahead and get it. At worst, you drill-out a rotten capsule and put in a $2 Panasonic capsule, hide a 9V battery inside that ample case, and run an XLR out. Since nobody you know has another mike like this, they won't know that it is bogus under the skin. (Oh... you might need to leave the power cord on, wired to a 7W light bulb in the case, so it "gets warm" like a tube mike should.)