[Chas]

The PM speaker will require a power resistor to substitute for the field coil. The OEM speaker is also equipped with a hum bucking coil, to use a PM an additional 20% in capacity should be added to the "filter output condenser". Same OEM field coil speaker also has the output transformer for the'42's. Even with a PM speaker the output transformer is required.

You may find the info here helpful to determine the correct output transformer...

http://www.radioremembered.org/outimp.htm

Might also want to check the Push/Pull input transformer that feeds the '42's. That, could have an open winding too.

GL

Chas