Tube: only one half lights up (faintly)
It's quite possible that if you get the other half of the tube lighting, everything will fall into line.
There is some shielded twisted pair wire leaving the 6.3V pads on the power supply board. This goes to pins 9 and 4/5 on the 12BH7 socket. If the connection to 4/5 is only connected to one of those pins, then you'll have one half of the tube not lighting, and one half of the regulator not functioning.
