That filament was always supposed to be DC powered but 12VDC operation would have been a better idea in hindsight or even running them at 25V.
My plan for this one is to run it off a BH power supply with it and the power transformer in a separate chassis. The amp chassis will also have to have mains running to it as the filament windings for the CCS tubes need to be as close as possible to the tubes. So that will be 4 transformers for this one and all in the largest Galaxy cases. Half the size of the ESX for a far more complicated amp... should be fun....