Have you got room for a chunky rectifier? say a 25A bridge, and if enough spare volts if only drawing 1.5A then its well inside a LM338 reg or you could get fancy and use a big pass transistor. But for the brass washers a 5A reg costs I'd use those and keep the current at 3A or less per device.
this all assumes spare volts on the winding and enough current to allow for loss through the regulator.
If you,ve got 18-19V to play with and can supply the total current for them, I imagine 12 x EL34
? then wire em in series as pairs at 12.6V.
DC heaters so your single runs won't create a fluctuating field and away you go.
I'm personally a bit against series chauffage of valves as one heater goes pop and nowt lights up and then you have to find the duffer.
One of my trusty Sovteks developed an intermittent contact on a heater pin, probably due to being pulled out and plugged back in too many times during testing on very tight sockets. It could have been tricky if wired in series.
The Idea seems tempting but overall I think it opens more cans of wriggly things than it seals.
OK keep up the good work I'm off out. My gear is getting salted away and boxed up for a few months until the building work and dust subsides.
I have a couple of refinements to add to my much simpler EL34 project when I get it back out but in the main it's pretty darn good. If a bit wimpy at 30W compared to your beasties.
If it drives a pair of ESL57 or 63 with no dramas and it should, then I will be a happy camper.