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  #46  
Old 10-28-2010, 02:22 AM
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Giulio Maiocco Giulio Maiocco is offline
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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
Attached Files
File Type: pdf Scan design pt1.pdf (683.9 KB, 71 views)
File Type: pdf Scan design pt2.pdf (974.5 KB, 36 views)
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  #47  
Old 10-28-2010, 11:32 AM
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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
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  #48  
Old 10-28-2010, 01:44 PM
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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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  #49  
Old 10-28-2010, 03:17 PM
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  #50  
Old 10-28-2010, 03:39 PM
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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?
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  #51  
Old 10-28-2010, 04:11 PM
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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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  #52  
Old 10-28-2010, 06:21 PM
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  #53  
Old 10-29-2010, 09:43 PM
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Dunno if this adds anything to the discussion, but here's RCA's patent covering early Color Flybacks.

Cheers,
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  #54  
Old 10-29-2010, 10:59 PM
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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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  #55  
Old 10-30-2010, 08:33 AM
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  #56  
Old 10-30-2010, 05:49 PM
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Quote:
Originally Posted by John Folsom View Post
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,
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  #57  
Old 10-30-2010, 07:32 PM
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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.
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  #58  
Old 10-30-2010, 08:09 PM
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Frankenflyback!
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  #59  
Old 11-04-2010, 04:50 PM
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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

Last edited by Tomcomm; 11-04-2010 at 06:03 PM.
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  #60  
Old 11-04-2010, 08:17 PM
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Quote:
Originally Posted by Tomcomm View Post
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.


Quote:
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.
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