When these drivers were used in the theatre systems, a dedicated field supply was part of the equipment. It powered all the field coils in the system, which could be up to six compression drivers and woofers in total. The circuit was simple; power transformer, rectifier tube(s), choke and filter capacitor. The old field supplies usually still work fine when they can be found, but are quite scarce these days.

Generally I use a bench type variable voltage DC supply, like the ones made by Lambda, Kepco and others. One needs to be found with the correct voltage range and adequate current rating. If you would like to build an original style field supply, let me know and I'll send you a scans of the schematic diagram.