[Charlie]

That's correct. Your set does not have a power transformer, and your filaments in the tubes are wired in series. Take a look at where your A/C line comes into the set. One side of the line goes to the switch, and the other side of the line goes to a chassis ground. This is why you want to use an isolation transformer.

Also, something else I was noticing looking at the Sams... the speaker in your set uses an electro-magnet, not a permanent magnet. Because of this, you'll need to make sure that all speaker connections are made while powering up this set. If the speaker isn't plugged in, you won't get any B+ voltages.