[morzh]

I dont get it. When you say it draws 8A, it is on the filaments side right? You measured current in series with filament winding? In order to draw that much you cannot have shorted turn. Shorted would 1) make the xfmr draw power on its own with no load, 2) would bring all voltages down, including its own winding so your tubes would draw very little if anything. Not the whooping 8A.
Shorted turn acts like a shunt, drawing current fir itself and starving the load, not adding to it.

See if your tubes have phil short to other electrodes.... I dont know but something doesn't jive here.