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#1
11-28-2011, 02:52 PM
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Testing a 21EAP4 Predicta CRT
A friend dropped off a Predicta Holiday today for me to check out.
I'm missing the #4 adapter, but was able to hook up the universal adapter. I get a filament glow with 2.35 volts and no shorts, but absolutely no emission. Any suggestions before I try to rejuvinate it ?  
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#2
11-28-2011, 03:18 PM
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under the motto of "1st do no harm" I would try it on another working set and see how it looks. I know that some CRTs may have odd pin outs (found this out about predicta CRTS a while ago), so you could triple check how the socket is wired to confirm you UA settings. I have also had decent performance even with dead reading CRT's not great but decent. Lastly are you sure its a 2.3 and not a rebuilt with a hotter filament? again a quick power up of the set with a VOM on the filament will confirm what voltage its been getting. so to sum up,
confirm pins by checking to see how the socket is wired check filament voltage try in a working set if available.
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#3
11-28-2011, 04:06 PM
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Well how about that! I put an ammeter on the filament supply and had less than 200 mA - it should be 600. I nervously turned up the filament supply until I have 600mA and found the voltage was right on 6.3. So it was either rebuilt or perhaps there's a different model 110 degree CRT designed to run on 6.3 ?
That got the emissions flowing. After about 20 minutes, I'm right at the bad/good boundary  Thanks for the excellent advice  
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#4
11-28-2011, 04:15 PM
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I just noticed this "6V" stamp on the CRT. I wonders if using this picture tube has much effect on the series strung filaments since it was designed for 2.35 ?
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#7
11-28-2011, 11:39 PM
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According to Sams, there's a thermistor in series with the tubes with a cold resistance of 400 and 11 hot.
I haven't opened up the set yet, but will soon.
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