Apologies for the delay, it took a while to find my two 866A's... I powered them up using a bench PSU and got similar results for both valves. Both pulled nearly 6A when first switched on, then settled to 4.6A @ 2.5v bang on after 5 minutes, so your reading of 4.4A isn't too far off. It might tax your tfmr a bit at first but see how you go.
Andy.
Andy.