[Radioroslyn]

So here the deal. W/o the speaker connected the power supply no load (all this HV w/nowhere to go) #56 keeps charging up and charging and charging till it get to it maximum voltage rating @ 450v. It's still charging up and up. After that happens it shorts from being exposed to too much voltage. This in turn put a terrific load on the rectifier tube (80 tube) and it shorts. With the 80 shorted it takes out the HV winding on the power transformer.

To find out what is going on w/your set unplug from the ac line, remove all tubes, and lamps. Used the schematic to make sure that the resistances on the transformer windings match the schematic and what there are supposed to be connected to. You may have something miss wired from rewiring the transformer.
If all that checks OK then replace all of the tubes and lamps EXCEPT for the 80 leave it out. Power it up and measure the ac voltage across the two small pins (2 and 3) of the 80 socket. If all is well should see about 600-700vac.

If that checks OK then replace #56 put the 80 tube into it's socket and connect your dc voltmeter + to the + side of #56 and the - to the chassis. Should see about 250vdc.

GL
One angry 80 tube !!!!!! Pic stolen from the net.