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

3 Nov 1998

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Subject: Re: CRT decay
Author:  classiccmp(a)u.washington.edu at internet
Date:    11/3/98 7:18 AM

...
  < 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.  This very same process goes back to the 1920's when thoriated
cathodes 
 were 'rejuvenated' by heating the cathode above its normal operating 
 voltage for several minutes to boil up the thorium mixture of the 
 cathode. This wasn't always successful but I have several friends who 
 can attest to getting better performance from old UX-99 triodes of the 
 early 1920's by this process.

 Marty

 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

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 Subject: Re: CRT decay
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