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  #61  
Old 11-04-2010, 10:42 PM
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Tom used a word in describing his set - that word was ancient.
That is what this set is/was - ancient.
Regardless of any elevated voltages or current I am convinnced that old age claimed this flyback - 56+ years, billions/trillions of electrons flowing through 38 awg wire - it was bound to happen.
Early television engineers never designed/dreamed of ANY set lasting for decades - even the ludicrously over-built Zenith sets of the late 60's and early 70's were/are disposable items.
Same goes for countless items...cars...wristwatches...refridgerators...NOT HING is designed to last ad infinitum.

Last edited by RobtWB; 11-04-2010 at 10:51 PM.
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  #62  
Old 11-04-2010, 11:10 PM
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RobtWB is exactly right. Even in the day, under warranty, flyback failures were NOT an uncommon thing. It is impossible to know if Toms operation of his 21CT55 chassis at 420VDC B+ and 27KV HV hastened the demise of his flyback. But EVERY time I turn on one of my "" ancient " TVs, I fear for my flyback transformer. I certainly would NOT recommend operating a vintage color TV at the outside design maximum limits as Tom did, but these old flybacks WILL fail, even at nominal operating conditions. Just the way it is.
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  #63  
Old 11-05-2010, 12:07 AM
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Originally Posted by John Folsom View Post
RobtWB is exactly right. Even in the day, under warranty, flyback failures were NOT an uncommon thing.
Tell me about it, RCA had a big problem with flybacks in the CTC101 set from around 1980. I had such a set, and yes the flyback blew up after a few years. I miss that set, it had a nice picture, with the comb filter.
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  #64  
Old 11-05-2010, 12:23 PM
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Originally Posted by wa2ise View Post
Tell me about it, RCA had a big problem with flybacks in the CTC101 set from around 1980. I had such a set, and yes the flyback blew up after a few years. I miss that set, it had a nice picture, with the comb filter.
They had a recall & upgrade kit on that chassis. I put in dozens of those in the early 80s. The "IHVT KIT". Great performing chassis!

Charles
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  #65  
Old 11-05-2010, 02:10 PM
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How things are (properly) designed depends on the application.
TV sets - should last a long time under moderate (home) conditions, but not cost more than people can afford. Repair or replacement is assumed rather than regular preventive maintenance.
Phone co. central office - designed to last 25 years almost certainly - assumed to be supporting an ongoing revenue stream with minimum maintenance (actually, design for minimum lifetime cost) and minimum failures. Put more money into the parts with expectation of getting it back in ongoing revenue.
High-tech mil gear - designed to extreme limits in some cases to be able to get extreme performance - needs to be ready when needed, but this may be achieved by constant maintenance in addition to basic reliability if necessary - spare no expense (compared to other categories, anyway)
Automotive electronics - toughest combination of performance, life, low maintenance, and controlled cost - auto manufacturers do NOT want any significant warranty returns of a $30,000 product for failure of a small part, and it has to meet these requirements in repeated environmental extremes.
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  #66  
Old 11-05-2010, 07:14 PM
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Quote:
Originally Posted by old_tv_nut View Post
How things are (properly) designed depends on the application.
High-tech mil gear - designed to extreme limits in some cases to be able to get extreme performance - needs to be ready when needed, but this may be achieved by constant maintenance in addition to basic reliability if necessary - spare no expense (compared to other categories, anyway)
How true! This maxim was repeated in my 22 years of Avionics Maintenance:

"Designed to last a lifetime, or until a Aviator misuses it, whichever comes first"

Guess which happened first....
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  #67  
Old 11-05-2010, 08:00 PM
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Maxim these days is 'takes a high school education to fix it, college education to break it.'

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  #68  
Old 11-05-2010, 08:15 PM
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Originally Posted by old_tv_nut View Post
Automotive electronics - toughest combination of performance, life, low maintenance, and controlled cost - auto manufacturers do NOT want any significant warranty returns of a $30,000 product for failure of a small part, and it has to meet these requirements in repeated environmental extremes.
I wish that they cared about that when they made that 72 Ford Pinto I had back around 1980. Constantly breaking down.
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  #69  
Old 11-06-2010, 10:04 AM
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Last edited by andy; 12-07-2021 at 01:32 PM.
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  #70  
Old 11-06-2010, 01:31 PM
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Quote:
Originally Posted by andy View Post
I ran into a situation repairing a computer power supply that might be relevant. The power supply had the usual load of bad caps, plus an overheated inductor. It was a simple toroidal inductor with 9 turns of heavy gauge wire, so I rewound it with the same gauge wire. Within minutes of testing the power supply, the coil had gone up in smoke and got hot enough to unsolder itself, so I replaced it with a new coil and all was well.

In trying to figure out what happened, I discovered that the ferrite core had become highly conductive (as in less than 1 ohm across). This basically turned the coil into a little inductive heater. I'm not sure whether the ferrite becoming conductive caused the original failure, or if the original failure (caused by bad caps) caused the core to break down from heat. Either way, it seems like the same thing could happen to a TV flyback core, and would make rewinding impossible. It's definitely something to check.
Toroids used in SWMPs are usually made by winding a strip of a silicon steel alloy. You would measure a low resistance from one side to the other, but since the ends of the strips are open it would not act as a closed loop or turn. Yours may have shorted between one of the layers of the strip and would behave as you described.

I don't know what the core is for the RCA John Folsom is rewinding, but if it's ferrite, MO=Fe2O3 or the ilk, the ferrite has a high electrical resistivity and shouldn't suffer that type of failure.

John
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  #71  
Old 11-06-2010, 09:42 PM
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Last edited by andy; 12-07-2021 at 01:32 PM.
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  #72  
Old 11-06-2010, 10:50 PM
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I don't think the ferrite cores on these vintage flybacks suffer from any changes in electrical resistance with heat. I believe they were fired like a ceramic, though maybe not at that extreme of temperature. Their only weakness, literally, is their brittleness.
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  #73  
Old 11-06-2010, 10:53 PM
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Powdered iron I can believe. It would be pretty strange for ferrite to change that much. Not that strange things don't happen.

However, I was surprised to see the large range of conductivity for various ferrites spanning six orders of magnitude. This table gives the properties and normal uses for ferrites and powdered iron.

http://www.ferroxcube.com/prod/assets/sfmatgra_frnt.pdf

John
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  #74  
Old 11-18-2010, 05:14 AM
ws407c ws407c is offline
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RCA 21CT55 #8802897 is Dead

Hi Tom , If you were to sell your 21ct55 how much would you ask for it ? I am looking for one of these sets in any condition and am looking to get an idea how much I might have to spend if one comes across my path. Thank's , Dave
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  #75  
Old 11-18-2010, 12:31 PM
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What are 21CT55s Selling For?

Dave..........I assume you know the condition of mine from reading this thread? There is no cabinet so its value is strictly as a laboratory test bed for various "experimentation". Presently I"m using the CTC2B chassis to determine what's involved in making it accept Component 400 line video in addition to its present standard 270 line Composite video. This is the only roundy I have. I have no intention to ever sell it. I would suggest you inquire of VK members Steve Kissihger or Bob Galanter or John Folsom what they paid for theirs or what they think a 21CT55 should go for. Lotsa luck...........Tom
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