Hi Les – instead of replacing the field coil from an electrodynamic speaker with a resistor, I have had good results using a solid-state field coil replacement. Here is a link to the circuit and original construction article published by the Antique Wireless Association:
http://www.antiquewireless.org/uploads/1/6/1/2/16129770/37-a_solid-state_filter_choke_or_field_coil_replacement.pdf
As stated in the article, the circuit provides 60 Hz ripple suppression in excess of 60 dB, far in excess of the original field coil acting as a choke.
Gary
