Okay, from the new angle it looks like it is okay, it looks to be the 10K resistor.
One shortcut that is generally true (but not always) is symetry of the output tubes when they are in a "Push-Pull" configuration such as yours. So checking voltages, resistive components, and wiring, if you measure from the same points between channels. This is also "somewhat true enough" for the 2 tubes in a push pull circuit. The differences occur primarily when doing resistance checks due to how the transformers are wound.
Now back to your situation with the power supply resistor. As already mentioned, pull the output tubes, and see if the resistor heats up. If so: there is a wire dress issue- something is touching the chassis that should not, or a stray blob of solder is shorting something out you may also have one or possibly two shorted output transformers. If it does not heat up, you may still have a shorted Output transformer just deeper into the windings. If it does heat up, Diconnect each output transformer in turn. The one that is disconneted when the reisistor does not get super hot is the bad one.
Other things to be mindful of initially: The hum balance control shold be centered. Also check to make sure the resistor shown to the right of each output transformer in the schematic is not shorted and that they are correct values and that the outputs taps that are not used are isolated and not shorting to anything else.
Doing voltage tests use only one hand and know where you have the other hand so you are not inadvertantly grounding youself - if you accidently make contact with a wire. When you do- you know it, as you can feel your heart respond. If the meter is not autoranging, set it for 1000 volts. If the resistor does not heat up, check for voltage on both sides of the resistor and make a note of it. Then check for voltages at each winding of each output transformer, Also- make sure there is a load on the outputs whenever the finals are installed. Preferably a speaker on each channel and on the correct impedance tap. This is important because that load determines current flow through the plates. It will effectively alter the turns ratio which in turn influence the atual plate load- if not high enough, the plates draw too much current. The voltages on the schematic will likely be low compared to what you see. As long as there is syemtry between channels, there should be no real concern at this time.
With tubes removed you should see anywhere from 300 through 370 volts measuring from the plate to chassis. It may seem high, but the output tubes place a load resistance of their own into the circuit, and in a good circuit, the voltage drops due to that load.
