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The DC CT100
I bought the CT100 dsuski had for sale. The owners are a very nice young couple in DC with a 1915 house that is drop-dead gorgeous. Kudos to them for saving the CT100! I brought my Sencore CR70 to test the CRT and LC75 to test the flyback.
The CRT: The filaments tested good for continuity. My CR70 was only able to get up to about 6V driving the filaments but they glowed nicely and did not burn out. I got no short indications. The cutoff responded very sharply but I could adjust it within the cutoff block. The emission then showed no meter movement. Increasing the cutoff at that point did show emissions. Is this an indication of a gassy CRT? I need to re-read my CR70 to see if they mention this type of indication. The flyback: I pulled the focus and HV rectifier tubes and did a ring test. It read 9 rings with the yoke still connected. I think the flyback is good. We agreed on a price with the strong possibility that the CRT was gassy and that the flyback was good. The cabinet needs work but its recoverable. The chassis does not appear to have had much work done on under it. Pictures attached. Tomorrow I will get it out of the back of my SUV and see if I can take a look at the getter. I suspect it will show air. I do not see this CT100 on Pete's list. It is #8001214 with cabinet #81. Dave Last edited by Zenith6S321; 11-23-2013 at 07:22 PM. |
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So that's who it was, congrats!
RE cutoff If it had nothing then jumped up very high on emission suddenly, it's likely gassy. That's the gas regulator action people talk about, it shows nothing till you reach the breakdown voltage of the gas in the tube then it conducts fully. I suspect you'll see ate up getters when you slide the neck stuff back, but at least you have a solid cab and chassis.
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Evolution... |
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Yep that's what the meter did. And I have just skimmed through the manual again and it is clearly a case RTFM (Read the FINE Manual)! I wish they had put that information with the rest of the normal testing operations. My bad. I think I will keep this set intact in hopes of the day someone (hopefully ETF) can rebuild them.
Dave |
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Oh well, at least it was saved from the landfill..
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Benevolent Despot |
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Quote:
Pete |
Audiokarma |
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At least the "gas regulator tube" action means its just gassy and not
fully up to air, so no internal corrosion. |
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Saw the thread title and my first thought was that it would take one hell of a big vibrator or dynamotor to run a CT-100 from DC power....
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Yeah, and a whole lot of car batteries!
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Here is a picture of two of the getters and the purple ionized gas shown in the small circle. The getters did their job and they are all used up.
This CRT probably has way too much air, but have people been able to re-flash the getters for a little more life? Or are the cathodes just too poisoned by the time the getters show wear? I'm gonna need to watch more bandersentv cabinet refinishing videos before I attempt this cabinet restoration. Under the chassis it all looks original, white peaking coils included. The HV cage also looks untouched. The tuner seems to be missing its cover though. Dave Last edited by Zenith6S321; 02-22-2015 at 06:54 PM. |
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Quote:
I have access to a small induction heater, and have tried reflashing getters on gassy tubes in the past (but never on a CRT). Heating the getter loop up is easy, but I haven't managed to get any visible deposit or any improvement in gas content. I suspect that the initial flashing evaporates substantially ALL of the barium content, and reheating the getter is pretty pointless after that. Once the getters look that bad, there is far more gas in the tube than even a full new getter would be able to handle anyway, much less whatever remnants you could hope to liberate by reflashing the old tabs. |
Audiokarma |
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It should be pointed out that even tubes with apparently good getters can be gassy enough to not work, so the appearance of the deposit on the neck is not a reliable indicator of whether the tube is still good or not. In either case once the cathode has been poisoned, there's no alternative but to cut the neck off and rebuild the tube.
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Evolution... |
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Quote:
http://www.saesgetters.com/sites/def...Features_0.pdf that says once the getter is heated to 800 deg. C there is a chemical reaction that raises the getter to 1250 deg. C and this event is visible by the quick change in color and brightness. Did you see this when you flashed the getters? They do say that using too much power will also result in not enough barium deposited. Sounds like all of this is a real art. |
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Quote:
Dave |
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There is a lot of interesting technical discussion of getters in RCA's 1962 "Electron Tube Design" manual, which is available online in a few places. Apparently, some types do only yield about 50% of the free barium on initial firing, but once the tube goes gassy, presumably the bulk material left in the getter cup starts oxidizing, as well. Getters are packaged under vacuum, and stored in an inert atmosphere before installation into the tube. Sitting for decades in a gassy tube can't do them much good, even in an unfired state. |
Audiokarma |
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