The way that Bandersen describing is one way to do this, the adjustable power resistor is another.
Using a resistor such as,
https://www.digikey.com/en/products/...WA210/11644319
Very cheap at under $7, and 1k won't put any real load on the filament transformer at all.
To be wired up like so,
http://suzaku.live-evil.org/CRT-POWER.jpg
And starting with the resistor slider set to the lowest extreme, (0 volts) just slowly raise it up until you get the 0.55 volts you need on the heater for the tube.
This is how I'd do it anyway.
