[Ron Ramirez]

Yes, it is correct. Without that dot where you drew your red circle, the 75 tube would be receiving plate voltage, but the plates of the other tubes would all read 0 volts. And there would be 0 volts on the screen grid of the 42 output tube as well.

That is a junction point for the B+ line of the set, which distributes high voltage to all four tubes in the set (I am not counting the rectifier, obviously). If you study the schematic carefully, you will see this clearly.