The stock power supply produces a nominal 460 volts DC at 80mA, with a 120v 50/60Hz primary supply. The voltage increases fairly linearly to 490v at 50mA. This winding and the primary are responsible for most of the heat generated.
The 6.3vAC winding is nominally rated 1.2 amps. That's a conservative rating, but I have not explored where the limit is or how it interacts with the other windings' heat generation. I cannot recommend exceeding that rating.
