[Arran]

 I have a better idea, forget about the 25L6 and it's goofy tapped winding, and replace it with a 50L6, then connect the rest of the tube heaters, and it, in series with a dropping resistor or capacitor. Then you can order up a more generic power transformer with a 6.3 volt winding, for the 6X5, and a 160-0-160 volt high voltage winding. I don't know why the power transformer went bad in this radio but the 6X5 was likely not to blame, at 160 volts per plate it wasn't being overvolted enough to arc over, and since the set uses AC/DC tubes it wasn't being overloaded current wise, so it was probably a shorted filter cap to blame. 
Regards
Arran