The 5998 has to be run with the proper bias to get the most out of it. So it's cathode resistor has to be 1/2 the value of the resistor that would be
used for a 6AS7. Then the transformer and rectifier has to be able to handle over 250ma. That leaves only a few rectifiers that can handle the current
The 3DG4 the old original 5AU4 or the 5U8C. No 5U4 type can handle this current not even the 596 or 5U4GB at 270ma. Add the 16 ma for the 6SN7
and it is 266ma that would be drawing over the 270ma to recharge the filter capacitors.
Silent One I will take a PIX but I have to dust it off first.