You can set the mains input selector to the LOW position. This will increase the CRT filament voltage somewhat, and will increase the brightness at least a little. It also increases the LV regulator dissipation, but this is OK, at least in the short term.
Does the brightness "double peak" as the Intensity control is advanced? Does the spot defocus? If so, the CRT is just plain weak. Many of these were allowed to run 24/7, and wore out the tubes.
Is the CRT HV transformer black or brown potted? If brown, that is another problem, well documented.
Keep us posted on your progress, good luck!
