CRT decay - test-drb@ccmp.vtda.org

2 Nov 1998

...
  < Don't CRT filaments degrade with use? 
I've seen this on other
 < workstation monitors from Sun and HP, typically ones that were used as 
...
  It the common characteristic of all valves (tubes)
with heated cathodes
 that over time emission will decay and gain(brightness) goes away with 
 it. 
...
  < big-ticket item, the local TV repairman had
cylindrical devices called
 < "boosters" that could be inserted in the circuit between the plug on
 < the back of the CRT and the set's CRT socket to extend the life of a 
...
  It got back some emission for a while but the
overvoltage generally 
 killed the tube. 
...
  < dim picture tube.  I don't really know what
it did, but I suppose it
 < was something like a step-up transformer for the CRT filament voltage. 
...
  That was it's exact function. 
There is also a way of 'reanimate' darkened tubes. Since the
most usual cause is a deformation in the emiting layer of
the cathode, the idea is to 'rebuild' the emiting layer. This
involves over heating with up to double power (Watt). The
parameters to be used have to fit the tube. This method is
also only real usefull for b&w tubes. Depending on the kind
of tube and usage this will lead to some additional 500 to
1500 hours of usage. The process can be repeated, but not
infinite. Since there is no new coating made - just a bit
mixed up of the existing. The basic why is just that thru
normal operation the electron emiting will always be from
the same spot(s) and the coating will degenerate over the
usage.

DISCLAIMER: I am not a master of physics or chemistry nor
do I know the exact english terms - I just using the process.

Gruss
Hans

--
Ich denke, also bin ich, also gut
HRK