[Station X]

Bill.

There's something strange going on here. The valves in this set have their heaters wired in series. This means that any break in the heater chain should cause all the valves to go out.

The fact you're measuring the SAME AC voltage on both pins of each valve indicates that the heaters are drawing no current, yet they're lighting up. That's impossible.

Let's try another approach. Switch off the set and set your meter to AC volts. Clip either lead of your meter to one of the brown wires leading from the mains transformer to the heater chain. Now switch on the set and probe the other brown wire on the mains transformer. You should see a high voltage.

Now follow the heater chain which starts at the brown wire your meter lead is clipped to. It will go to pin 1 or 8 of a valve, then leave on the other pin and go to the next valve pin 1 or 8 and so on until it returns to the mains transformer.

Probe each valve pin as you come to it and post the readings (12 in all) here.