I think you pose some pretty good evidence that these are engineering samples. I'd definitely buy that. Thanks so much for sharing, this was fascinating!
Id agree thats its possibly a engineering sample, but it could possibly be a radio test bed for there tubes they made to see how it reacts when in operation. We can all assume the possiblites are high coukd of been a radio that one of there engineers threw togther to see if he could sell it off for sone extra cash which still be the sane thing an engineering example.
You probably already know them, but a couple of years ago I have been in contacts with a company called triad magnetics. They make all kinds of transformers, also to specification, including output transformers for audio. That may be a remnant of the earlier radio company. If you like, I can send you the information.
