CRT's almost always fail due to low emission. On a
B&W symptoms are dark pix, negative pix, streaking of
bright areas, slow warm up & overly bright whites with no detail or any
combination of.....
Best test is darken the room, turn down the bright & contrast.
If it looks a lot better its the CRT 99%.
All fixes are risky ( except a new CRT )
Rejuvenation, only use a MODERN CRT checker for this made
after the early 70's.
Brighteners only work on some sets.
Most sets have a low ohm resistor in series with the filament.
It can be jumped out to give a little more E but again risky.
As far as waking it up goes regular use will usually improve things
but its a process that goes on just like people getting old &
slowing down......
73 Zeno
