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  #1  
Old 02-01-2018, 12:44 AM
EdKozk2 EdKozk2 is offline
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Rca ctc-5h

A few weeks ago my son and I picked up this set in the Chicago area. Today I finally repaired a simple emission type CRT checker I've had sitting around since last year. I hooked up the checker to test the guns of the 21AXP22a CRT. It took about 2 to 3 minutes of waiting to get these readings on the scale. I also noticed there is a purple glow toward the forward CRT elements. Is this condition normal for this type of CRT that's been idle for years?
If the CRT is usable still, then I will proceed with a recap. The power transformer checks OK. Haven't checked the flyback yet. I still have two other B&W sets to recap and test.
ED
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File Type: jpg MVC-001S.JPG (36.2 KB, 123 views)
File Type: jpg MVC-006S.JPG (36.8 KB, 99 views)
File Type: jpg MVC-011S.JPG (37.3 KB, 81 views)
File Type: jpg MVC-010S.JPG (35.7 KB, 62 views)
File Type: jpg MVC-009S.JPG (35.1 KB, 63 views)

Last edited by EdKozk2; 02-02-2018 at 11:48 PM.
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Old 02-01-2018, 01:03 AM
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It the CRT passes the short and gas test I would take a chance and recap the electrolytics.
Phil
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Old 02-01-2018, 01:04 AM
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Have you tried your tester on any other CRTs? That might tell you how much weight to give the tester's opinion, especially if you test some known-good CRTs as well as a dud or two. Testers vary in quality/sophistication, like other devices.

In my experience, CRT testers don't always tell you the whole story. I have seen CRTs that look weak on a tester, but make a fine picture when used in a TV. The best tester of all is a television.

Also, if a CRT hasn't been used in a long time, it's common for it to "wake up" and show stronger emission after it has cooked for a while on a tester at normal or slightly elevated filament voltage.

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Old 02-01-2018, 01:45 AM
EdKozk2 EdKozk2 is offline
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I tried the tester on some good and not so good B&W crts. The results reflected what I knew from in set testing. I agree Phil, in set testing is the best indicator.

The crt shows no shorts, but the gas test seems quick to decline and slow to rebound? Looks like I have good reason to proceed.
Thanks Phil and Phil.
ED
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Old 02-01-2018, 01:34 PM
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Purple glow between elements of an electron gun is not a good sign. The voltages a crt tester produces are rather low compared to what the crt will be using when it is in operation.

Typically, if you see inter-element purple glo, and you use a Tesla coil to test if the tube is gassy, you will find that the entire gun area in the neck will light up with a gassy pink/purple glo.

I purchased a 15GP22 about a year ago. On my Beltron tester, I was getting very high emission readings, but there was faint inter-element glow in the gun elements. The With a B&K 465 crt tester the glow is much fainter. When I applied the high voltage from my Tesla coil, the entire neck area lit up bright pink/purple showing that the tube was gassy. You can also see a blue-violet glow between the G1 and G2 gun elements

There are 2 ways to be sure if the tube is gassy, Tesla coil or an operational chassis. I have found anything else will not be a definitive test for gas.

Three photos of gassy 15GP22. Beltron emission readings, Inter-element glow on the Beltron crt tester, and Lots of glow with the Tesla coil.

Posting good photos of the kind of glow your 21AX produces would be more helpful.

All that said, there is still a possibility your tube may be OK.
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Old 02-01-2018, 03:47 PM
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I learned in the process of testing my now confirmed good 15GP22 in my Westy that, without a working chassis, the best test of a CRT's suitability is a Tesla coil and a Sencore CR-70. If cutoff responds normally, and the Tesla coil fails to produce any substantial glow, then you likely have a winner. Given your description, I think you have a dud though.
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Old 02-01-2018, 06:24 PM
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I'd be interested to see what people are using in the tesla coil arena.

If you know your tester and it's gas test well the more heinous gassy CRTs will have a distinctive fail characteristic....
One nutty thing you could try is to take a monochrome chassis with 20KV or more of HV and connect the CRT leads from the chassis to one gun (with clip leads), then connect the HV. With the brightness at minimum it should produce a center dot on the screen, but if the tube is gassy there will be an arc inside the tube between the HV and the electron gun.
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Old 02-01-2018, 07:23 PM
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Quote:
Originally Posted by Electronic M View Post
I'd be interested to see what people are using in the tesla coil arena.
Likely something like this... widely used in science labs, by tube builders, and perhaps stock yards for decades.

https://www.amazon.com/Oudin-Coil-Te...rds=tesla+coil

https://www.amazon.com/Electro-Techn...J0RRDTNFN23F1B


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Last edited by jr_tech; 02-01-2018 at 11:04 PM. Reason: add second link
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Old 02-02-2018, 01:16 AM
EdKozk2 EdKozk2 is offline
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After seeing your center picture Bob, I tend to think the crt has seen better days. Ben I don't have tesla coil tester but I bet your correct about it being a dud.
I find it difficult to get a good picture of the purple glow in the crt gun. I'm still going to recap the chassis and try the crt just for the experience. The last photo is with my camera set for nightime exposure, for more light.
Ed
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File Type: jpg MVC-005S - lightened.jpg (135.8 KB, 72 views)
File Type: jpg MVC-011S - lightened.jpg (102.0 KB, 74 views)
File Type: jpg MVC-010S.JPG (38.1 KB, 73 views)
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Old 02-02-2018, 09:38 AM
old_coot88 old_coot88 is offline
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Quote:
Originally Posted by jr_tech View Post
Likely something like this... widely used in science labs, by tube builders, and perhaps stock yards for decades.

https://www.amazon.com/Oudin-Coil-Te...rds=tesla+coil

https://www.amazon.com/Electro-Techn...J0RRDTNFN23F1B


not affiliated
jr
We had one of those as standard equipment, called it the Cattle Prod. Used it for 'cleaning' rebuilt CRTs before installing them.

Rebuilts tended to arc due to contaminant particles. The Cattle Prod made the particles incandesce and fly around until they stuck somewhere, thus minimizing arcing after installation.

Last edited by old_coot88; 02-02-2018 at 01:27 PM. Reason: DUMB TYPO
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  #11  
Old 02-02-2018, 12:49 PM
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Quote:
Originally Posted by EdKozk2 View Post
After seeing your center picture Bob, I tend to think the crt has seen better days. Ben I don't have tesla coil tester but I bet your correct about it being a dud.
I find it difficult to get a good picture of the purple glow in the crt gun. I'm still going to recap the chassis and try the crt just for the experience. The last photo is with my camera set for nightime exposure, for more light.
Ed
Word to the wise only recap the power supply and sweep circuits. The rest should be able to last past a check of the CRT with HV applied.
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Old 02-02-2018, 06:02 PM
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init4fun init4fun is offline
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Thank You gents for explaining and showing pictures of the tesla coil . I have one in my collection that came from the contents of the Radio/TV repair shop I was lucky enough to get , and wasn't quite sure what it's use would be in TV repair work .
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Old 02-03-2018, 12:09 AM
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ohohyodafarted ohohyodafarted is offline
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You can find "tesla coils" listed as Master High Frequency on ebay. Used in the field of cosmetology and skin care. Make sure you buy a "working" unit. These units heat up and burn out when used for prolonged periods of more than 5 minutes. Dumb cosmetologists often over work these units and burn them out.

You will need to make your own metal pointed probe if you buy one of these with the glass skin care probes. But it is cheaper than paying $250 for a new one.

https://www.ebay.com/itm/Vintage-Mas...4AAOSwGJlZL6Bu
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Old 02-03-2018, 09:35 AM
WISCOJIM WISCOJIM is online now
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Quote:
Originally Posted by ohohyodafarted View Post
You will need to make your own metal pointed probe if you buy one of these with the glass skin care probes. But it is cheaper than paying $250 for a new one.
And I had been trying to sell one of these at radio meets for $55 as a quack device. Now that I know they have a good use, I'll be holding on to mine! (Thanks, Bob!)

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Old 02-03-2018, 09:38 AM
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Good to know those work for that purpose...Now I know what to look for.
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