Picture tubes and the brightening thereof

[compucat]

There are many methods that get results, none of them truly permanent. Before I got a rejuvenator (which only works on '50s and '60 tubes, it's an old one), I would connect the filament to a 12V power supply for maybe 20 minutes or so to bring the cathode back to life. It usually worked. Sometimes just using the set daily would be enough to bring a tired tube to normal brightness. Most times though, a dim tube means the cathode emissive material is just used up, time for a rebuild or replacement.