Back in the days, folks used to slightly increase the filament voltage, from 6.3V to 7V or more. Sometimes you could even recover the CRT and it would work with the nominal filament voltage.
This is a really unique piece of hardware and of course you might want to try this technique only if you have no choice.
This is a really unique piece of hardware and of course you might want to try this technique only if you have no choice.