[RodB]

No need to unsolder the wires of the transformer primary. There should be a 0.002 mfd cap connected to pin 2 of each 41 output tube but that shouldn't interfere with the resistance measurement. If you want to verify that the primary is open you can remove the two 41 output tubes and measure between pin 2 of each socket. If you measure around 350 ohms then it's good, if you measure an open circuit then the primary is open. If it's open, you may get lucky and find one of the transformer primary leads has separated from the transformer winding wire. To check this you have to remove the transformer, open the transformer metal shell and carefully cut the paper covering layers till the primary wires are exposed.

You should try to find out why the primary is open. It's usually one of two things. Either the grid bias of the output tubes is wrong causing them to conduct too much current or the transformer winding failed from old age/corrosion. The grid bias on each 41 tube at pin 4 should be around -25 volts. If this is OK then it's a good chance the transformer winding is defective. One other cause may be the B+ is too high. I'm assuming you monitored B+ when you first powered up the radio.