[Arran]

So what is wrong with the speaker again? I think that the 650 Ohms denotes the field coil, though it may be inductance rather then DC resistance, if it reads 742 Ohms it's probably fine. I can't think of anything else that would be giving you a 742 Ohm reading, the output transformer primary is usually lower then that, the secondary will be lower, as will the voice coil, and the hum bucker winding. The hum bucker is in series with the secondary of the output transformer, but in opposite phase. The field coil looks like it's connected to the two fat pins on the speaker plug, the output transformer secondary is connected across the two small pins, with the center tap connected to one of the fat pins. I think that the speaker was probably manufactured by Rola, though it could be a Lansing speaker.
Regards
Arran