You are bringing this old scope to life, and you correctly start by evaluating its power supplies.
What is very useful to have for this step, is a variac (a variable autotransformer) that allows you to increase the AC supply voltage practically from zero
This is a good precaution when not knowing what can be wrong, and what could burn out.
Your scope has a linear regulator, meaning that after the input transformer and rectifiers, the unregulated supplies will rise proportionally with the AC you apply with the variac.
If you are not in a hurry, you can then rise the AC in steps, like 25%, 50%, 75% or finer coming close to the 110 VAC, over a period of a day or so, to give an opportunity for the electrolytic capacitors to regenerate.
While you come up to the nominal voltage 110 VAC, you can watch the voltage on the +50V, which is the "master" reference for the other supplies. You can check that at some point it stabilizes, regulates, and verify that it is 50 V
If it does not reach 50 V, then you may have a failure in it, and this will be reflected in all the other supplies. The failure can be in the supply itself, or in its load (the rest of the instrument)
I don't know how much you can disconnect the power supplies from the rest of the instrument, and if you can, this helps to limit the extent of the failure to the supplies themselves, and not to some short elsewhere.