[Ron Ramirez]

That speaker isn't original. The original was electrodynamic, which means it had a large coil of wire in back which acts as an electromagnet. This is called a field coil. It also serves as a filter choke in the power supply.

You can convert a radio which originally had an electrodynamic speaker to a PM type, but then you have to install a power resistor or a choke to replace the field coil. A resistor is usually used, but then you have to increase the size of the electrolytic capacitors a bit to take care of the hum.