I've been researching filament supplies for a 811A. Most people say it has to be DC. A few have said you can use AC if you use a balancing pot and maybe try Steve Bench's circuit. But everyone likes Rod Coleman's. I like AC because it's easier, and makes less heat. DC has to have a bigger filament transformer, lots of big caps and will make something like 10 watts of heat. Rod Coleman's circuit needs a bigger transformer (more current and voltage), a circuit board, a bid UGLY heat sink and will make like 24 watts of heat.
A 845 will make a lot of heat itself, but it's the good kind of heat (above the chassis).