[Arran]

It looks sort of like a balanced armature permanent magnet type, those were quite common in farm battery radios in that era since G.E had not yet come out with alnico 5 at the time to allow for a PM dynamic. Take a look at the volume control, it's mechanical, it looks like it uses that slide thing to put tension on that reed. International Radio was in large part responsible for developing what is now known as the AC/DC set, and they were pioneers in the use of plastic cabinets, at least in North America.
Regards
Arran