This is correct. I have an FG504 and such a TM504 that I had to correct the phasing on. The FG504 in trying to reach a +-050VDC rail stacks a 32VDC and a 25VAC on top of each other for both positive and negative rails, and if the 25VAC windings are out of phase it never gets there, so the regulator is below its dropout voltage and you get major hum.
EJP
