BTW,it was discovered by TEK CRT manufacturing that CRT life is directly
related to filament voltage. As little as 0.1V too high, and CRT life
suffers. A lot of 2213/2215 CRTs were replaced under warranty for this
reason, and the HV xfmr had a half turn removed from it's filament winding.
This is interesting and consistent with what I know about electron
beam emitters used in electron beam microscopes and lithography. (See
below.)
since most TEK CRT filaments get their supply from the HV
oscillator(excluding the old 500 series..),regulation and proper HV voltage
setting is essential.
Sounds like an excellent point to keep in mind.
Thanks,
Jon
P.S. Emitters are coated to promote thermionic emission, then a
Wehnelt to enhance the field effect and shape the emission, and so on.
But the aging of such emitter systems is HIGHLY dependent on the
temperature at the emitter itself. This, in turn, depends on large
part with the current used. Variations in lifetime of emitter systems
I worked with were from 1-2 months to as long as 20-24 months. Same
units in every respect except for the procedures used. Many of these
systems used expensive current control systems to set the emitter
heating current, but that really wasn't enough. The systems that ran
longer were ones where regular protocols were used with disappearing
filament optical devices to observe the _temperature_ at the tip, not
the current, and where that was done regularly. The very best were
those where the disappearing filament devices were calibrated on a
regular basis using NIST calibrated tungsten filament standards driven
by expensive current controls and getting new calibration standards
every 100 hours of calibration use (or less.) Those consistently got
the longest lives out of their 'heads.'
In these cases, getting the absolute MOST out of the emitters was
important, though. For example, lithography happens faster (which
means more production value) if the electron beam is more intense. So
clients want to operate at the absolute ragged edge. That's different
than an oscilloscope requirement.