I have a Tek 2213 in great condition, but the trace is very dim. It
is an old scope from a tv station, they may have just left it on all
day, otherwise it doesn't seem to have any use on it at all. I know
this is a common problem in older scopes, but I've never actually
understood the reason. The phosphors on the crt still glow well, i.e.
if you press beam find and concentrate the trace it's fine. Is this
just a high voltage problem, or is it just the end of the CRT's life?
Filament in the CRT going bad? HV section failing? I know this
happens quite often, but I never understood why. Could someone give
me some expert advice, help educate the younger generation? I
apologize for the simplicity of this question, I just wanted to get to
the bottom of this directly instead of going off of what I've "heard".

Thanks for reading,
Steve