[Arran]

That 39-770 looks like it's one of the Tropic Models with a tuning indicator light, if that's what the hole in the escutcheon is for bellow the dial glass. It's strange that those were the only Philco models that came with that feature, they were very common on some Rogers and Rogers built sets between 1934-36, less complicated then a shadow meter and arguably more responsive then a Magic Eye. The way they work is that the light goes dim when you tune the set to a station, at least that's how it works on my Rogers Ten-60. Philco must have had a different department engineer their Tropic models as they seem to be almost completely different from their domestic U.S models for some reason.