[6GH8cowboy]

This is a DC regulated fillament supply.
In this case the fillament regulator transistor was bad (under load). I am of the opinion that this is a most over engineered fillament supply. Both voltage and current! There is absolutly no reason for it. Once the CRT is pluged up and lit, the load is constant. What ever the final setting is to manualy bring the fillament voltage back to spec. that's where it stays. No fancy regulation nesessary. AC mains wont change that drastic while your testing in even the worst part of the world.
This had to be some kind of marketing thing.

Oh yea, the instructions say to set the switches first. That's because misconfiguration can present itself as a short on the fillament line if misconfigured.

Set the switches first, check the settings again... turn it on.