kivy31, thanks for posting. Nice nostalgic piece. Can you post a better pix, that's not as fuzzy? And is there any writing at all, anywhere on there?
There is no shortage of 2-box units from the '40s and '50s that show up at flea markets, CL, ebay, etc.... There were a lot of them sold in those years. That was before the advent of the more typical configuration of standard loop detectors, which weren't seen as much, till the mid or late 1950's.
As far as the "value", as I say, there's no shortage of them that show up. But perhaps if yours is truly from the '30s (as opposed to the '40s or '50s), you might find some interest. But the truth is, there's not a lot of vintage detector collectors out there. And those that do collect, have usually long since found their sample pieces. What is more interesting to vintage collectors, is the standard coil types that were capable of finding coin-sized targets from the '50s, as those were oddities for their time, and a variety of efforts came and went during that time.