Sinusoidal power supply 36 V 400 hz

That's a good suggestion, Les. A 50/60Hz power transformer would work well at 400 Hz. I, too used one as a tube amplifier output transformer in my teens. You could use one with a 24V - 0 - 24V winding. Connect the output of a single amplifier running on +/- 25V to one half of the winding and take the power output from across both.