[Arran]

I think it would come under either American Bosch or United American Bosch. American Bosch made sets for the American Westinghouse company around that time as well. For some reason there was a tie in between Northern Electric and American Bosch, that made sets with almost identical chassis so I'm guessing that Northern Electric must have been making American Bosch sets under license. Grimes-Phonola/Dominion Electrohome used to do this with other U.S companies.
As for the Essex marque, Hudson owned Essex, and also owned the Terraplane marque, which apparently started under the Essex marque until Essex went away in 1933, so maybe the car radio was for a Terraplane but why mention the Essex name inside?
Regards
Arran