I was initially surprised by the 40-80Kh number also. The difference I think
is that in a scope the tube is not driven as often (duty factor) or as hard
(especially white background applications) as a CRT is in a raster scan
application. Therefore I would expect digital scopes using raster CRT
displays to have shorter lives than analog scopes or, say, 2400 series
digital scopes which vector write an analog scope type CRT.
In CRT raster scan applications, I would agree with 10Kh though they seem to
last a lot longer now than 10-15 years ago. Remember those old 12"
monochrome CRT monitors for PC use in the early 1980's (e.g. for HP80 series
desktop computers)? If we left those greenscreens on 24/7 on our burn-in
systems, they'd be toast in a year. After the first wave had to be replaced,
the production operators would turn them down at night before they went home,
and left them down whenever they did not have to see the display. In later
years (the systems ran 17 years I'm proud to say), we couldn't even find
replacement "NTSC sorta" analog input monitors. And how about those EGA
color displays from around 1990?--tubes went fuzzy fast with Windows
applications. We had a whole room of the things with bad tubes (and also
broken electronics). Of course it didn't help that people ran, ahem, "screen
saver" pictures on them when not in use.
If the scope CRT number is truly closer to 10Kh there would be a lot more
junk scopes around our operation, as most are left on in production, through
two shifts, 5+ days a week, in auto sweep mode (with the brightness turned up
too high to boot). To the best of my knowledge, we've never pulled a CRT in
any of the scopes, and most of those go back more than 10 years (including a
couple Tek 465Bs, Leader 100Mhz dual trace, a couple Tek 2200 series). Any
more we would junk them for whatever cause if they failed--I have two I got
that way. One (465B) I restored and the other (TAS465) I haven't found a
service manual for yet. Both have good CRTs though.
The only dim scope tube is in our trusty 571 (bought from Tucker many moons
ago) which exhibits the double peaking on the intensity control that others
have mentioned. The trace is pretty dim when cold, though improves with a
good warmup. I watch it closely to make sure nobody just leaves it running.
Quite frankly, I don't think there is anyone left besides me that can run it
anyway so it is in a way "out to pasture". I've wondered if a replacement
CRT is available for them from anybody....
Don
