[Arran]

The only reason I can think of for installing the wire would resistors in series with the two legs of the high voltage winding is that the B+ may have been too high, either for the 6X5s to handle or for the rest of the set. I found out the specs online for a Thordarson 24R06U, here they are:
H.V Winding 375-0-375 150 ma D.C
Rectifier winding 5 V at 3A
Filament winding 6.3 V at 4.7 amps
So it looks like you can dump the 6X5s and replace them with a single 5U4/5X4 which is what Commander "Cheapskate" MacDonald should have used in this set in the first place. As I said before many time I have no problems with a 6X5 is they are used properly, like in a 5 or 6 tube table radio, but not in a 10-12 tube console.
Regards
Arran

Correction, you may want to try a 5V4, it can handle more B+ current then a 5Y3/5Y4 but the filament only draws 2 amps instead of 3 amps.