[Mondial]

Have you checked the resistance of the speaker's field coil winding? Applying 100 VDC while testing it will not make it work if the field winding is open. With an open coil you may still hear very low audio from residual magnetism in the iron core.

What signal source are you using to check the speaker for sound? If you are hearing anything at all through the output transformer, then chances are the voice coil and transformer are probably ok.

The additional mica cap across the 75 plate to ground is not really necessary for operation, but you might want to reinstall it. It might have been added as an RF bypass, or to modify the tone characteristics of the radio by rolling off the high audio frequencies. It appears that this cap ( 250 pF ) was added in later production and is shown on this schematic:

http://www.nostalgiaair.org/PagesByModel...013877.pdf