RCA 21CT55 #8802897 is Dead

[andy]

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[Findm-Keepm]

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

Cheers,

[John Folsom]

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.

[Findm-Keepm]

Originally Posted by John Folsom

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.

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,

[andy]

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[old_tv_nut]

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.

[John Folsom]

Frankenflyback!

[Tomcomm]

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

[miniman82]

Originally Posted by Tomcomm

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 roundies

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.

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.

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.

[RobtWB]

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.

[John Folsom]

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.

[wa2ise]

Originally Posted by John Folsom

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.

[kx250rider]

Originally Posted by wa2ise

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

[old_tv_nut]

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.

[Findm-Keepm]

Originally Posted by old_tv_nut

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....