Hi everybody!

I'm sorry to hear about this mishap with the flyback transformer, I think it's one of the worst "oh no!" moments.

I don't know the color flybacks, but I rewound some B&W ones without problems, and from what I saw, they are less critical than one may be led to believe. I even rewound a couple that were wave-wound in a more conventional "layer" winding, these still work flawlessly. In my Bush TV22 I rewound both the primary (bad enamel on the magnet wire crumbling away, so I decided to fix it) and the EHT winding (this one was wave wound and covered in tar, but the acid in the tar corroded the copper). As a result the TV works very good, I'm 600-700 volts short on the EHT, unfortunately I ran out of wire while rewinding. Using a test pattern, I cannot detect image distortion or ringing, so I'm really happy with the results!

A question for John Folsom, if I may ask: what kind of substance do you use to keep together the winding when you pi-wind? Now I have a wave winding machine too and experimented with some shellac, it works, but it's quite slow to set.

Thanks

Giulio Maiocco

P.S.: Sorry about my so-so English...

Giulio, thanks for posting this information. Your work looks good - I know handling the fine wire is very difficult. Also, your English seems fine to me.

I wonder if you have an oscilloscope and high-voltage probe, and can check the shape of the flyback pulse?

I'm curious (again)and was looking at the schematic of a TS-905 Motorola regulator. These are shunt regulated high voltage supplies that, in the case of the Motorola, sample boost and that gives the 6BK4 grid bias thru dropping resistors. It seems to me a balancing act between the CRT beam current and the Shunt regulator tube to keep high voltage near constant voltage. Since high voltage was 34 KV, It makes me wonder if the higher than normal RCA HOT current came mainly from too much B+. Having no regulation would lessen the load on the high voltage as the shunt regulator would be biased to cut-off. I read the drive was OK to the tube (waveform voltage) but was the negative voltage on the HOT normal or too low. Higher RF voltage on the output would be expected but this would tend to break down the high voltage winding. The primary failed from what I read but these generally have around 6 to 8 KV RF on them so breakdown is usually rare.
Since the picture was wonderfully linear, I don't think the flyback had any shorted turns until failure.
When running before the failure, was the flyback running hot? I don't have a schematic on the CT2 series but the shunt regulators seem to be similar in the older sets.
Any opinions?

Hi again

To old_tv_nut: I'm happy you liked my work rewinding this FBT, just to let you know how boring it is, it counts 2045 turns of 31awg wire on the primary, and close to 3000 turns, 2960 to be exact, of 36awg wire on the the EHT winding, all done by hand, so not an easy task.

Yes, I do have 2 oscilloscopes, a Tek 545B and a Solartron CD1400, but at the moment I don't have the needed high voltage probe, I should indeed buy one if I can find one at a good price. As soon as I succeed at locating this probe at a fair price, I'll check the flyback waveshape, no problem!

Cheers

Giulio

DAveWM, my method is to unwind a flyback and count the turns and measure the wire gauge. And yes, I will be at FAWG.

Giulio, That is beautiful work you have done. I don't know if a layer winding approach could be used for color TV flyback transformers. At some point, I may give that technique a try, but I have many avenues yet to explore with my universal winding machine.

while the coil is winding, the ziz-zag structure is all that is needed to hold the coil together. The tall, thin high voltage secondary winding is also self supporting and stable, but I apply a topcoat of silicone RTV rubber to protect the coil and give it additional mechanical stability.

John Yurkon, I am not sure about the third harmonic tuning. I suspect you are correct, but I have no verification of this. I have a book published by Phillips which goes into great theoretical detail into the design and modeling of the windings on a flyback. And while this is helpful in as general knowledge, it does not really help me to know how to modify my recipe to achieve a particular result. I expect some trial and error is ahead of me.

Good morning

sorry to hijack this thread, if any moderator feels this is too much, please remove or move my reply!

@ John Folsom: I'm far from an expert, but I think that layer winding should not be a problem, maybe some changes are required in the circuit in order to obtain as specified performances.

Also, thank you about the info on the pi winding, and now I think I know what I'm doing wrong, the wire needs slight more tension, as until now the "layers" gives a spongy feel when touched and the width of the winding creeps up.

BTW, please have a look at the 2 files I attached, I think this is interesting

Cheers

Giulio Maiocco

I'd have to go look over the schematic to refresh my memory on what all besides the horizontal sweep and HV is unique to that chassis. But one idea might be to break down the flyback section into separate devices; perhaps a flyback from a newer color set to give the sweep, and a simple solid state high voltage supply for the 2nd anode? It should be much easier to solve this problem for this set, than for a CT-100 with the weird deflection angle and integral convergence HV feed, etc.

Charles

Giulio, thanks for those great articles. I will have to go to school with them.

I agree with Charles, it should be possible to substitute in a flyback from a later vintage set, say a CTC10 or so. It would tack some exprimenting, but I think it could bedone.

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Andy, I know at some point, flyback designs used the layer winding approach. But all the flybacks I have seen up through the 1950 and early 60s were universal wound. When did they switch over? Did this coincide with the use of transistors?

Flyback Info
 

You can measure the dimensions of a flyback with a time domain reflectometer (TDR), a precision digital ohmmeter, an LCR meter, and a micrometer.
The inductance of a newly rewound flyback will probably be different than the original.
You should change the inductance of your new flyback by adjusting the core gap rather than adding or deleting turns to the coil.
Remember, the inductance is inversely proportional to the gap.

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Dunno if this adds anything to the discussion, but here's RCA's patent covering early Color Flybacks.

Cheers,

Findm-Keepm, not sure if I can use this idea to modify the recipe in the flybacks I am attempting to wind, but thanks for the interesting patent.

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Sanyo gives the step-by-step in their patent, albeit for a Solid State sweep circuit. Good info on the materials too.


I could spend weeks looking at patents - lots of cool info.

Cheers,

IIRC, all the flybacks I worked on at Motorola in the late 60s had layer-wound donuts (probably bi-filar) with Nomex paper, and potted in a fire-retardant-containing polyester compound, with a silicone outer "tire". The compound was a balancing act, since more fire retardant was better for flame resistance, but increased the lossiness of the stray capacitance, and therefore changed the tuning and caused more heating in the coil.

At Zenith, they developed a combination of silicone oils that duplicated the electrical characteristics of the potting compound, and therefore there could be a quick turn-around of trial designs, since they didn't have to be sent through the potting process; and furthermore, windings could be changed as desired without throwing away a bunch of cut-and-try prototypes. The engineer's bench looked like a horror movie, except that a flyback would be in the big jar instead of a human brain.

Frankenflyback!

Last Chance for Tom's 21CT55
 

Well now that the heat of this thread has subsided and a lot of good FBX info conveyed, I wanted to repeat portions of my initial post that described where I was coming from with my chassis-only 21CT55. Why I feel no guilt regarding my methodology in pursuit of realizing this ancient set’s picture-quality potential.

.................I decided in October 2007 to reactivate the beast after 40 years in attic storage and use it as a test bed to determine and demonstrate in photos, the picture quality this 55 year old RCA CTC2B chassis was capable of producing. As such, it was not constrained to replicate the original circuitry in every detail or even operate to the '55 RCA spec. I jacked up the +400v B++ supply to above +420v with silicon diodes and got a horz boost of almost 1KV. I intend to start reducing the CRT Ultor HV from its present 34KV to the 28KV range while doing a full convergence at each reduction level to determine if I loose ANY picture quality.

Note: All screenshots in the Photobucket below were taken at the reduced ultor of 27kv and a B++ of 420v. No abuse here. It has run at these settings from the screenshots of Nov 16, 2008 until the FBX blowup of March 21, 2010. At no time did the FBX coils get above 135 deg or the B++ fuse current above 260ma. I’ve never opened the HOT cathode to measure its current so I don’t know its value. The CRT is a 21FBP22A, the most advanced and possibly most rugged of the latest RCA roundys

Yes, I brutalized this valuable historical item but there are at least five other 21CT55 restorations on this forum alone. I believe I've succeeded in my goal of demonstrating the 21CT55's ability of displaying exceptional picture quality…………………….


That said, I realize the only reasonable chance of resurrecting this CTC2B chassis is thru the knowledge and skill of Vk member John Folsom who remains optimistic that he will produce a replica of RCA’s second color FBX, possibly this year. I am so grateful that he consented to give it a try. Truly this effort rivals the rebuilding of the 15GP22……as far as I’m concerned. Thanks John for your interest and dedication ………Tom

See, this is where you loose me.

Let me just preface this by saying that I don't personally care what you do to your set; it's yours, and you're free to do with it as you please. But you can't say the things you just said, while in the same breath claiming 'no abuse here'. Doesn't make any sense. As I said before, I've never encountered a schematic text that instructed techs to do anything with reading current from a fuse holder. If you want to know HOT current, you read it from the HOT cathode. Since you didn't, I can promise you that it was most certainly higher than it ought to have been. Despite your assurances that the coil never got hot (again, no 'specs' as to what is deemed 'safe' as far as temperature is concerned), it's my conclusion that running the set the way you did is what caused the failure.

I won't speculate on how 'rugged' one tube is over another. I can only tell you that the RCA manual I have in front of me has the 21AXP22 CRT operating at a 25kv ultor, maximum designed voltage being 27.5kv (see http://frank.pocnet.net/sheets/137/2/21AXP22.pdf). The 21FBP22 is designed to operate at 20-25kv, and has the same maximum ultor rating. Any time you exceed a manufacture's recommended ratings, you are asking for trouble. That's all I'm going to say about that.


And I hope he succeeds. I can only hope that you learn from this experience, and check HOT cathode current correctly next time. These old parts were never designed to be pushed beyond their original limits, which many will agree were probably being pushed by the factory when operated within design tolerances.

Again, no bad blood. I just hope that you look for improvements in other areas in the future, because pushing the HV high again will likely lead to the same result. Best of luck.

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.

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.

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

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.

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....

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

lol

I wish that they cared about that when they made that 72 Ford Pinto I had back around 1980. Constantly breaking down. :thumbsdn:

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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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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.

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

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

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

I paid
 

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.

Thank's Tom , Bob for your replies :thmbsp: 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 ;)

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?

CTC-4 and later had only partial DC restore in the luma. All chassis had DC restore in the chroma, which is necesary to prevent the color tracking drifting in the opposite direction of the most prominent color in a scene.

In the CT-100, DC restore was done on the individual R,G, and B drives, so both luminance and chroma were DC restored.