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#1
03-31-2009, 10:44 PM
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crt testing
I have a chance to get an early color set with the round crt. I tried testing the crt but it is acting unusual. all the guns check really good at first. If I leave the tester hooked up keeping the filaments lit and wait about 10 minutes and redo all the tests the emissions are lower than before. My tester is a b+ k 465. the scale goes to 1,000. At first all the guns check at about 900. Later they all run about 600. That is still in the good range but is this telling me the tube is questionable or my tester is dying? there are no shorts and it still passes the "life test". This is the only crt I have checked that does this. Thanks, Doug
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#2
03-31-2009, 11:36 PM
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It sounds like they all test the same in any event. That's good because you want them to be in balance. 600uA is still pretty decent. As tempting as it is to hypothesize why it's doing this, I'll refrain.
But, I would check for shorts again after you observe the lower emission. Also, recheck the filament voltage setting to see if it's drifted. Also, while you're checking the emission observe the gun area and see if you see a blue glow that might indicate that it's gassy. How's the G1 cutoff? With such a high initial emission I'd expect it to be well within range. I don't think I've been very helpful, but you made me curious. Maybe you should repost in the color tv forum. John Last edited by jeyurkon; 03-31-2009 at 11:40 PM.
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#3
04-01-2009, 12:03 AM
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My guess is it's the tester fading after being left on so long.
I doubt it was meant to be left on for 10 minutes straight plus it's old enough it could need some servicing itself. I have a 465 but I like the 466 better.
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#4
04-01-2009, 02:06 AM
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I have a 465 also and there's not much in there to fade or fail. There are two electrolytics in the power supply and two in the restore function that should be replaced or tested.
If this behavior still doesn't occur for other CRTs then I'm not as sure that the tester could be failing, unless you see the filament adjust drifting. John
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#5
04-01-2009, 09:37 AM
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Why not measure the filament voltage with a meter as the CRT is being tested? It is possible the filament transformer in the tester is heating up and dropping the voltage.
__________________
John Folsom
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#7
04-01-2009, 06:41 PM
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If you start from cold, do the readings return to 900?
If not, then my guess is the tube was rejuvenated.
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#8
04-01-2009, 07:39 PM
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Well, I think I will be ok. I recapped the tester and now the guns check as follows. Blue holds at 920, green at 940 and red at 870. They now just sit there and do not change. I wonder now if the problem was caps starting to get weak and the extra transformer load of running three filaments at the same time on my tester.Now I will have to retest my b&w crts and see if they change from what I remember. Thanks for the tips, Doug
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#11
04-01-2009, 10:56 PM
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Quote:
The electrolytics were probably increasing in leakage as they warmed up dropping the HV used for the emission test. Congratulations on figuring it out and repairing your tester. Did you get the set? John
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#12
04-02-2009, 10:35 PM
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I had to. I have wanted a tube color set for long time. I would probably push an old lady down a flight of stairs for a set like this.I do like new technology, don't get me wrong, alot of people feel that the tube stuff is junk or outlived its usefullness. I on the other hand am drawn too it. I have placed a tubed b&w set on a stand in front of a perfectly good big screen set and watched it.
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