RCA 21CT55 #8802897 is Dead

[Eric H]

Originally Posted by JB5pro

Am I understanding correctly that u used your apparent vast knowledge to experiment with a virtually priceless object that being the flyback?

The Mona Lisa is a "Priceless object" a Flyback is just a TV part.

Someone simply asked for help, lets keep the rude replies in check shall we?

[kx250rider]

Originally Posted by Eric H

The Mona Lisa is a "Priceless object" a Flyback is just a TV part.

Someone simply asked for help, lets keep the rude replies in check shall we?

Yes. I've been a member here for a few years, and I don't remember any case like this where other members "ganged up" on another. Not shame on Tom; but shame on the shamers.

There are at least two AKers in this thread, who are lucky Eric and the other mods are tolerant, and lucky that I'm not a moderator here.

Charles

[John Folsom]

Unfortunately, Tom's flyback suffered a catastrophic internal short in the primary winding. The heat generated actually caused the HV winding to slump. But there is still some hope. His flyback is in a box beside my workbench. It has been partly unwound, and the winding "recipe" recorded. I have not yet unwound the HV winding. This flyback is a bifilar wound type, with most of the primary and secondary windings wound with two wires in parallel. This makes it that much more difficult to attempt to rewind. The HV winding is a single strand of approx. AWG 38 wire.

I have wound 2 color flybacks so far, one for a 15" Motorola color set, and one for a CT100. The Motorola flyback works, but it has lower impedances than the original, and has a big "dip" in the top of the flyback pulse, which is causing some issues with the gated circuits. So just having the winding turns count recipe is not all there is. More experimentation will be required to attempt to determine what parameters need to change. As for the CT100 flyback, it too measures lower in inductance than the original, and if failed almost immediately upon installation in the set. Unwinding it did not reveal an obvious defect. I suspect wire handling is a critical issue.

I have taken a break from coil winding attempts for the last couple of months, it is just too darn hot out in the garage to slave over a hot winding machine. And other project have managed to get on the bench ahead of the coil winding. But in the next month or so I will get back to it, and see if I can make more forward progress.


Here is a photo of the winding machine, a George Stevens model 225-AMVP universal progressive coil winding machine, made in 1964. Some of you may have seen this at my ETF presentation on coil winding.

I will report progress as it is made.

[rca2000]

Originally Posted by miniman82

I intend to start reducing the CRT Ultor HV from its present 34KV....'

and

'I jacked up the +400v B++ supply to above +420v'


I get a certain 'cringe factor', know what I mean? Not only was the 21AXP22 never rated for that votlage, but I severely doubt the flyback liked being driven that hard. How many times do we see people get warned again and again about HOT current, recapping, variac starts and the like? Seems obvious to me that the experimentation took it's toll, that's all I'm saying. I do hope the set can be fixed, but as I said I don't think you're likely to find an NOS one.

..

I have to put my "2 cents" in here too.
I agree that the "turbocharging" is likely what killed the FBT.Going to OVER 420V on the B+?? If it was MY set...and I wanted to put silicons in I would have put some "series resistance" in line with the diodes, say, 50 ohms/10 watts or so. This would have kept the voltage from going over the limit.

And...34 KV?? Man...that is HIGH Voltage!! I have worked for a LONG time on tv's and I have only seen a FEW sets that high, such as a FEW sony prjoo sets, and a couple of 36" CRT's, that were 35KV. Most others are UNDER 34KV. And ALL sets with chassis tubes were under 28KV, to the best of my knowledge!! I would NEVER DARE to run a 21AX at 34KV--I would be afraid that it would kill it, and if not-- some REAL X-rays would no DOUBT be produced--since those tubes did NOT have x-ray protection.

Having said this--your experiment DID produce a BEAUTIFUL picture--like I could not BELIEVE!! No doubt the super--HV and boost had something to do with this.

IN short--I look at it like a turbocharged engine--and an OLD one, at that. Say--putting a 12 PSI boost on an old Chrysler 2.2L--and SURE you WILL get a LOT of power and performance out of it-- probably 250HP--for a SHORT time...but not for LONG--as the old engine(or fly and CRT) will NOT stand it.

Once you get the set working again...I would suggest series resistance with the diodes to get no more than 390 volts, and no MORE than 26KV h.v., and NO MORE than 225 MA Cathode current.

As for the "discourse" I agree some of it was a bit "heated", but as it was pointed out--CTC-2B sets are RARE--and the "keepers of the flame" do ANYTHING they can to PREVENT them--or parts like FBT"S-from ENDING UP IN FLAMES, and thus--allowed their passion for their collecting hobbies to steer the discussion. Myself, I have a CTC-5, and it is NOT working yet--as I have little time to mess with it, working and all--but it DOES have and a near--perfect, CR-70 tested, CRT--and the fly looks good--and when I DO "get into it" I will NOT "stress things at ALL.

I DO hope you are able to get your set going again though. Best wishes to you.

Jack.

[Tomcomm]

Hi John, welcome to the fray. Glad you revealed your present involvement in getting my CTC2B FBX replaced. Your proposed complete recreation of the failed windings on my original core is a truly heroic undertaking. I’m fortunate to have you participate. Thanks.

Most members of this thread are resigned to the fact that no oem CTC2b FBX will ever be located and even if were, it would probably cost as much as a recent rebuilt 15GP22! This prompted a number of imaginative replacement solutions to be proposed here. Most consisted of combining the low voltage section of my original FBX with the high voltage “donut” from a working, similar RCA or other early color TV FDX , or drive a new HV tripler module from a modern SS TV for ultor . Unfortunately, it’s the original primary and low voltage windings that have failed and are cooked beyond repair. John’s proposed FBX recreation seems like the only solution here……providing it doesn’t cost me as much as a recently rebuilt 15GP22!

Pete D………. to answer your question: In the mean time, I will use the CTC2B chassis only as a hardware test bed and waveform only monitor for my experiments with external Component video inputs. Seems that the three components: Y, Pr,and Pb, are available on three of my DVD players. Y is the luminance with sync that has no 3.58mhz chroma messing it up so it can extend the baseband to 5mhz which equals over 400 lines resolution, where all our roundys cut off at 3.2mhz or 256 lines! I think I can extend my 21CT55's original final three stages of CRT Drivers to possibly 5mhz without chroma interference. It would be great to see the resolution chart wedge with its lines displayed to 400 lines without all the chroma artifacts we see now. Do any of you see a problem?

[old_tv_nut]

Originally Posted by John Folsom

I have wound 2 color flybacks so far, one for a 15" Motorola color set, and one for a CT100. The Motorola flyback works, but it has lower impedances than the original, and has a big "dip" in the top of the flyback pulse, which is causing some issues with the gated circuits. So just having the winding turns count recipe is not all there is. More experimentation will be required to attempt to determine what parameters need to change.

I'd like to put in 2 cents worth of speculation here.
1) I have no idea why the primary inductance is less than expected if the turns count and pattern is the same, except maybe the core gap has changed in the process of disassembly/reassembly. Don't know what kind of gap material was used in these units. When I worked on flybacks in the 60's, we used hard paper gap material in the lab. Later, a material containing beads of a specific diameter would be painted on the face of a mating part for production. This was bright yellow stuff you see on some parts.
There is a danger of upping the inductance by decreasing the gap, in that you will decrease the current at which the core saturates (a bad thing) -but if the gap currently is too wide, it is worth trying.
2) The dip in the top of the flyback pulse is because there is too strong a 3rd harmonic resonance in the HV winding.
a) I don't know if these old flybacks were supposed to use 3rd harmonic tuning - it was common practice by the 60s, especially for solid state sets, because the right amount would flatten out the plate/collector pulse and reduce stress on the horizontal output device.
b) I am beating myself on the side of the head, but it's not helping me recall what to do to modify the strength of the 3rd harmonic - probably involves choice of the dielectric material, but since you generally don't have options, changing the HV winding parameters - more turns and less layers or vice versa. However, as I think about it, it seems to me those kinds of modifications would change the frequency of the tuning more than the amplitude. Right now I feel really dumb, 'cause I used to do this for a living, and the one thing I'm sure of is I'm not remembering it straight.
c) just FYI, some later designs used 5th harmonic tuning to flatten the collector pulse even more - approximating a square wave by a combination of fundamental, 3rd, and 5th.

Edit: there is always the possibility that if you get the correct primary inductance, the ratio of 3rd harmonic amplitude will turn out to be correct -- fix the first obvious thing, and it may improve two problems.