RCA 21CT55 #8802897 is Dead

[wa2ise]

Originally Posted by old_tv_nut

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.

[miniman82]

Maxim these days is 'takes a high school education to fix it, college education to break it.'

lol

[andy]

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[jeyurkon]

Originally Posted by andy

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

[andy]

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[jeyurkon]

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

[John Folsom]

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.

[ws407c]

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

[Tomcomm]

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

[ohohyodafarted]

My 21ct55 was a steal at $975. I got very very lucky on this purchase. It had a very dead 21axp22. The crt was the original and was from what we believe was probably the first production run of 21axp22's. They used a 20 pin stem left over from production of the 15gp22's, to mount the electron gun assembly. I had the crt rebuilt at a cost of $500. Later the flyback took a crap and I was lucky that my best buddy John had a spare for me. Cabinette needed to be refinished too.

But based on the rarity of this set, I would probably say it is worth more than a working ct100 with a good crt. But that is only my opinion. I think that CT55's are vastly under appreciated. Everyone wants a ct100, of which there are many more. I think there are only about 8 or so CT55's known to exist.

Steve Kissinger paid more for his. But his was in better condition.

FYI: last year I acquired a 1st generation 21" Sylvania color set. Upon close inspection I discovered that it uses the same flyback as the 21ct55. Both sets were produced at about the same time. And both sets are equally rare.

[ws407c]

Thank's Tom , Bob for your replies I currently have 2 CTC-16 , 1 CTC-16X and a CTC-12 , 2 of which have rebuilt tubes from Scotty and perform quite nicely . I wish to do some sort of black level clamp/ dc restore to one of them and am very curious as to how the CT-100/21ct55 performs as to black level responses. I hope to find a 21CT55 someday and will keep a constant look out for one in hopes to have one as my daily watcher.Thanks again guy's !

[Robert Grant]

Originally Posted by ws407c

Thank's Tom , Bob for your replies I currently have 2 CTC-16 , 1 CTC-16X and a CTC-12 , 2 of which have rebuilt tubes from Scotty and perform quite nicely . I wish to do some sort of black level clamp/ dc restore to one of them and am very curious as to how the CT-100/21ct55 performs as to black level responses. I hope to find a 21CT55 someday and will keep a constant look out for one in hopes to have one as my daily watcher.Thanks again guy's !

In the meantime, if you find your new 21CT55 leaves you with no room for one of the 16's, let me know

[miniman82]

Originally Posted by ws407c

I wish to do some sort of black level clamp/ dc restore to one of them and am very curious as to how the CT-100/21ct55 performs as to black level responses.

FYI, I did some research into black level resto on CTC based sets (I have a 9, a 7 and a 4). I ended up running into an old service document that said black level on those chassis was reset during every blanking period when the blanking tube went into effect. So in theory no resto should be needed, but perhaps the restoration effect of the blanker is not what it should be?

[John Folsom]

Ken, email sent. Long and short, I do not have any spare parts. George Stevens Co. still has some gears and cams available, but they are expensive. The gears for the machine are non-standard, so are not available from the usual gear sources.

[Tomcomm]

Just finished installing the new FBX sub-chassis circuitry into the CTC2B chassis. No dynamic conversion, chroma keyer, color killer, chroma blanker pulses from the FDX are connected. Focus out of range, linearity, screens, gray tracking not adjusted.

Power input is 115vac, B++ adjusted for 378v producing 860v boost, Ultor is adjusted at min of 28kv, max is well over 36kv! HOT cathode reads 128ma. The big ultor voltage with a tiny HOT current indicates I need a HOT that matches this new FBX, namely a 6JE6A replacing the original 6CB5? I have to order one and its socket & cap.

The premature screen shots indicate I’ve got a long ways to go on this one to approach this 21CT55's previous posted shots.