[GarySP]

Welcome to the Phorum, Nate! The difference between an electrodynamic speaker and a permanent magnet speaker is easy. As the name indicates, a permanent magnet speaker uses a magnet core to drive the voice coil. With an electrodynamic speaker, an iron core is used, then wrapped with a field coil. When the radio is turned on, the coil magnetizes the iron core. Others here can give you more exacting information regarding the two types of speakers. The quality of magnets in that era was sketchy at best and not known for holding their magnetism. The electrodynamic speaker solved that issue with the electromagnet core. As magnets progressed PM speakers were used and electrodynamic speakers were phased out as the PM speaker was less expensive and simpler to produce. Hope this helped.
Take care and BE HEALTHY! Gary