@mulveling has confirmed my read that the heater would not be hooked up. (needs both pins to have a circuit). So KT150 would not light up and would not produce any current.
At this point I don't think we need someone with tube knowlegde, we need someone with a primaluna schematic to figure this out.
We all agree you should not have done any damage. We don't understand why you got music.
One other thing to check, follow your cables and make sure the preamp is actually in the signal path. I assume it is as you must be using it for volume control if nothing else, but you could be using your DAC or Roon.
Jerry