#1
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Dead picture tube? 17GP4
Pretty sure it's dead Jim, but just wanna run this past you.
17GP4. As I understand it, it's the much rarer version of the 17CP4, the only difference is that the 17GP4 uses high voltage internal focus, whereas the 17CP4 uses external focus magnet. And yes, this is the crt with the metal bell fused to glass. (That one threw me for a loop when I first saw it!) Anyway, the tv set is old as dirt so I'm not going to turn it on to test the picture tube. Probably wouldn't work anyway. Initially, I had tested this crt with my Hickok 533a, via adapter. It read 'bad,' but just barely at the line 'Diodes OK'. The pamphlet thingy for the adapter says some crts will be good over that mark, on certain testers. It also says some crts will test 'bad' and be good. TLDR: testing crts on the Hickok is just guess work! So I bought a proper crt tester. A slightly off brand, the Lectrotech CRT-100. Now I don't have a manual for this, but I do have the settings to use for this particular tube. Anyway, I initially tested the crt and got roughly the same reading, round about 2.5, right on the border between good and bad. So I tired the rejuvenate button. Long story short, it made it worse. Or maybe it didn't, I don't know. At any rate, it reads nothing at all now. But! It's not actually open, it is still there. If I super heat the filament it will give a faint reading, just above 1, but then it'll drop to 0 as it cools off. I did recheck with the Hickok to make sure my tester didn't just take a dump, and sure enough, the Hickok gave me the same nothing reading, and also would read a little bit on a higher filament voltage. Now just today I decided to try one more time. I set it to rejuvenate. And I noticed when I push the button - only when I push the button - I hear what I'd imagine is electricity arcing inside the tube, it's a very faint and irregular crackling. But it's in the bell, nowhere near the gun. At least, nowhere near the actual cathode, can't see anything happening there. Is that normal? Also, I'm fairly sure the tube hasn't leaked. Neither tester indicates it, and the tube's physical condition looks pretty good. The set itself (I found outside in the garbage) looked like it had been indoors its whole life until it got chucked. Anyway, how screwed am I? Pics or didn't happen: https://dl.dropboxusercontent.com/u/...esting_crt.jpg https://dl.dropboxusercontent.com/u/...ting_crt_2.jpg |
#2
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Mistakes have been made....Most CRTs that test in the high end of bad will produce a good picture (some may need a brightener). Don't EVER rejuve a CRT with a pre-late 60's tester!(unless it is stone dead and newer units have failed)...The early ones are too aggressive and ruin more tubes than they save (there are many old threads on rejuves here warning of this).
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#3
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Quote:
Normally a CRT just on the line will look OK especially in a darkened room where you dont have to run the brite & contrast high. Often at the shop a set would look like shit but when at home looked fine. We had all fluorescent lighting that was to brite & washed out the pictures........ 73 Zeno LFOD ! |
#4
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Both of those testers are garbage. Get a good Beltron or Sencore CR-70 or CR-7000. I use both, the Sencore when I need to thoroughly test a tube, the Beltron for a quick check (I leave it in my car) or for a gentle rejuv cycle.
Assuming you have trashed what may have been left of the 17GP4's cathode (which is very likely) you'll need to find another. The Early Television Museum lists one for sale from their inventory of NOS and good CRTs: http://www.earlytelevision.org/crts_for_sale_b-w.html In any case, you simply cannot rely on a CRT tester. Commit this to memory: the best CRT tester is a working set. I've gotten good pictures out of tubes with supposedly low emission, bad cutoff, imbalanced guns (in a tricolor kinescope), etc. The 17GP4 isn't too terribly rare, so little harm was done. Before you smoke something harder to find though, PLEASE replace that Hickok and the Lectrotech..... |
#5
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FML.
Well hey, the Hickok has never let me down when it comes to regular tubes. Granted I don't get to use it very often, but so far, so good. I won't be testing crts with it anymore though... And I'll be wary of that cheap pos Lectrotech. I've already (a while ago) inquired about that tube with the museum, they haven't replied yet. |
Audiokarma |
#6
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Quote:
Lectrotech test equipment was reasonally priced test to compete dollarwise to B&K. My first color generator was a Lectrotech, which seemed to work well! $40.00 less than the B&K model. That was 50 years ago. |
#7
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The Hickok is fine for standard receiving tubes, I use a 600A exclusively. I've just never had good luck with the CRT adapter for my Hickok. The Sencore is much more useful.
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#8
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Quote:
It can be replaced with a 17CP4, but it needs a magnetic focalizer. Anything other than a 17GP4, remove the 1V2. |
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