Thanks for the clarification regarding off-load voltage and rated voltage.
About the current draw... the schematic is for a stereo amp so I estimated around 96mA for two 6V6 and two EF86. The arrow at the node that reads 258V translates as "To other channels."
That said, maybe I'm reading the schematic wrong and the 258V reflects only that one side of the amp... but wouldn't you model the entire current draw (all tubes) on the power supply?
