RCA 21CT55 #8802897 is Dead
 

I originally posted the following message on May 30, 08 when my 21CT55 seemed to be performing at its best. It gave me the opportunity to rationalize why I did not restore it to original, since I destroyed the cabinet in making it into a table model to save space in my garage workshop in 1964........................


.................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.

Since I'm running the 21CT55 as a composite monitor, I disabled all the tuner, RK/IF and audio portions and opened all unnecessary tube 6.3v heater strings to allow the power transformer to run much cooler. I left all inactive tubes in their sockets and documented all changes for immediate reactivation. 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.

http://s677.photobucket.com/albums/v...2021CT55%20TV/

I do intend to refinish the surviving front panel of the original cabinet using the approach described by Bob G in his impressive restoration. I might even attempt to construct a pseudo pencil-box control panel,

On March 21, 2010 at 3:30pm my 21CT55 ate its flyback transformer in a cloud of acrid smelling white smoke coming out of the HV cage! I was out of the room for about 10 minutes so I didn't see it loose its picture and couldn't shut it down, so it just cooked. I was so shocked, I just killed the power without looking at the HOT and damper to see if their plates were red hot. I opened the cage and the FBX was still smoking. The HV doughnut was dropped down and dripping hot insulation stuff, a truly sickening sight. The B++ fuse had not blown because it was 1 amp! It should have been .5 amp since the running current was only 265ma. I checked my fuse box marked .5 A and the 4 remaining fuses were all 1 amp, bummer!

I lifted the doughnut back to where it should be, supported it with pieces of foam plastic and let it cool off for about 30 minutes. I put a current meter in series with a .5amp fuse and applied power. Remarkably, the boost voltage and B++ started to slowly climb and the picture came on as the current settled at 265ma, boost reached 780v, ultor was 27kv, all normal! Naturally, I was delighted. After about 5min,the screen went black, the current climbed to 480ma and the boost dropped to the B++ of 420v. The HOT plate started to glow so I shut it down. The FBX was warm. I pulled the damper, the yoke and all the HOT and rectifier plate caps and power up'd. The HOT grid had a normal 150vpp drive input, that was not the problem. All FBX windings measured nominal resistances, maybe they developed shorts? Anyway, I needed a CTC2B FBX, apparently a non obtainable item. So was this the end of my 21CT55?

Do any members have an operational CTC2B flyback transformer or know where I can acquire one? If so please send me a PM with details ......soon. Thanks, Tom

'ONLY' 265ma???

If any of my sets ever got that high, I'd pull the plug right away. Hell, I'm not happy with the 210 my 7 is at right now. You played with fire, and got burned. I don't think anyone will be willing to toss another unobtanium part your way, not with the kind of experimentation you've been doing. Just my opinion...

:tears: Sincerely saddened to learn of your misfortune. Hope you can find a flyback to repair that amazing set. I've enjoyed the many pictures you've posted of that set and the Sony monitor. The comparisons were jaw-dropping to me.
All the best!
Kevin

bummer - from the photographs you have posted that set produced an absolutely amazing picture
just a thought - since the set is heavily modified already, are there any flyback transformers for other sets that are close in specifications to the original? i know the ctc-2 and 2b chassis' are somewhat unique in their design - but i would think there should be something close in the early RCA line - hell there may be something in the 60's or 70's tube driven or SS sets from other manufacturers that are close in specifications - certainly no real need to keep it original -

BTW - i know where there sits a roundie that i have been thinking about snatching and doing just what you have done to the 25ct55 - improving it exponentially - with a few modifications - i know the purists will get up in arms - but hells bells it is just an old television - it certainly isn't like painting a moustache on the Mona Lisa

miniman82, are you talking about HOT cathode current or current at the HV fuse?

HOT cathode, I'm not aware of any current specification in any manual that tells you to read the HV fuse... It's not in my RCA manual, anyway.

Yeah, but the way I read it, I think that is what he was measuring. I could be wrong.

Current clarification
 

The first replier to my thread seems to consider himself the VK Safety Nanny and member attack Pit Bull. Has he considered getting professional help with his obvious anger management problem? Just my opinion..............

That said, my normal +425v current of 265ma is always measured across the HV cage fuse clips. RCA requires a 300ma fuse so the flyback is well protected. I usually use a 500ma fuse since I couldn’t find a 300ma item but accidentally used a 1amp fuse when the flyback cooked so it didn’t blow. This wouldn’t make any difference since the flyback shorted and was doomed.

My only “experiment” with the CTC2B’s power supply was the replacement of the big selenium rectifiers with small silicon power diodes. This simple and logical change raised the B++ from 392v to 425v or 8.4%, well within RCA’s safety margin. How many members performed this same “experiment” on their sets??

Sorry to hear the news. I don't know the #2 postor, and I wouldn't have said that myself. In my viewpoint, this hobby would be zero fun without any challenges, and this is no different from a situation where someone might restore a '38 Cadillac, and take it out for a Sunday drive and have a kid run a red light or something. It happens.

There are several AKers with 21CT55s, and hopefully someone will speak up with a good FBT. If not, I'd suggest doing some comparison research to see if you could use a different Fly in that set. After all, the basics are the same for the horizontal frequency and deflection angles, etc., among most all 21" color sets. With a little qualIfied engineering, I bet a later model FBT could be used, since your set is a working demonstrator and not a virgin timepiece.

Charles

Am I understanding correctly that u used your apparent vast knowledge to experiment with a virtually priceless object that being the flyback? If so... shame on you!
If you took that flyback to it's limits you ought to be forced to restore it by chemically softening the coil so you can unwind it in order to determine exact length and specs for the new windings you will replace by hand. After you spend countless hours doing that maybe you will learn your lesson to respect things properly. All the knowledge needed to get the most out of those TV's has been uncovered by many great men here at Videokarma.

Sorry to hear about your fly problem Tom. Does that mean your quest to engineer an S-video input to a CTC2B is on hold? ;-)

As to your question, yes, I replaced selenium with silicon in my operational CTC2 chassis, w/o a compensating resistance added, since in NJ where I lived at the time the line rarely went over 115 and was usually much lower (115 is the AC input spec for the CTC2). That chassis is now/still at ETF driving the rebuilt 15GP22 demo there, and since the line at ETF was nicely above 115, I added a 50-ft. extension to the power cord, which conveniently drops the line to around 115.

Pete

You've Gots to be Kiding!
 

But in the event you're not................I'll ramble on. My sacred FBT died of old age. It developed a short in the primary winding very near the core. I could see a tiny blue arc and a whiff of white smoke on the side of the winding near the core when I tried to restart the TV.

I did not cause this tragic failure, I wasn't even in the same room and the HV cage was locked. This FBT was toast, all dried out and brittle. It was non-repairable in my estimation. It had to be replaced.

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?

I know this is a long shot, but, how about rewinding? Has anyone ever successfully rewound a fly or had it done by a transformer company?

I have read about vert out transformers being rewound and I know they are much less complex, much like a power transformer.

---

Some of you need to take a deep breath and chill out. It's just a damn piece of equipment. Tomcomm's set may have ran at that current for 50+ years with no problem. But folks, it is a 55 year old transformer, and sorry, but sh*t is bound to happen. No one engineered these parts to operate a half century into the future. Furthermore, it's his set and his money and the idea of denying him the right to buy a replacement part (or do penance for that matter) is childish and ludicrous.

Correct me if i am wrong is your CTC2B the same as the CTC2 in the CT 100 that uses a 6CD6? if so according to the RCA receiving tube maual RC-21 "the average cathode current............... 200 max ma" . Whats up with 3R264?

The CTC-2B uses a 6CB5 which is spec'd for a design center maximum cathode current of 220 ma. Having said that, count me among those who aren't particularly sympathetic...or surprised.

The idea that anyone here could deny anyone else on this forum anything is what's ludicrous, taking someone's OPINION for fact is also childish...


That said, it is my OPINION that this thing burned up because of the 'mods' that were done to it. Maybe it's just me, but when I read things like:

'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.

Some of you collectors are certainly a strange breed...

The burden is on us,the keepers, the possessors. We must be good stewards of the rare and dimminishing.For every one good thing we do to preserve something there is at least five things we can do to destroy it.
No amount of chastisement from others could ever reach the level punishment that i would inflict on myself for hurting precious treasures.

You know, what the guy needs is constructive criticism and advice such as the replies from andy and kx250rider. Suggesting he doesn't "deserve" another flyback is asinine. Period.

Three days ago I watched someone drive a pick axe into the side of an NOS Sylvania color combo with a dead CRT. Guess I should have thrown myself between them. :sigh: Hate to tell you, but not long after we draw our last breath most of our "precious treasures" will probably be scrapped for copper.

Not until they pry them from my cold dead fingers and of those who will continue after.

Hi,

some years ago, I visited Marcel van Grinsven in s'Hertogenbosch. He had manually rewound the primary coil of a burned flyback for a 90° Delta shadowmask color tv set. The rewound flyback looks lousy, but it worked! I saw the set working with this flyback.

Meanwhile, he could replace the rewound flyback with a spare one.

I learned that rewinding a primary coil seems not as difficult as it looks like. The reclacing of the EHT coil with a coil from an other flyback model is much easier since the technical values are more similar. I have even replaced a Sojvet EHT coil for a coplor flyback with a ten-years older German EHT coil of a quite different color tv set.

Kind regards,
Eckhard

This is the last thing I will say on this, since I already clarified what I wrote:

I NEVER SAID ANYONE DID OR DID NOT 'DESERVE' (your words) ANYTHING. Stop putting words in my mouth, or meaning to my posts that does not exist. If you want to get butthurt about something I've posted, send me a PM. I don't sugar coat reality, I call it like I see it. My first post was my initial reaction to reading OP's post. My second reaction is: I'm not surprised it blew up. You're free (as I am) to give whatever advice you wish, if you have some issue with me personally contact me, and if that doesn't work, a mod.



I kill terrorists for a living, what's your release?

I would like to second this idea - if the primary winding is separable from the secondary. The primary winding depends mainly on its inductance for proper operation, since the distributed capacitance is not that large, plus, it is essentially in parallel with the yoke inductance. The secondary (HV) winding is tuned by its distributed capacitance, which means you need the same materials as well as the same winding configuration to get the original result in rewinding the secondary. Using an existing good secondary coil in case that has failed also makes sense, since you will get both the designed inductance and distributed capacitance.

I wish the OP good luck, but also want to say that I personally never would raise the B+ , HO current or HV to improve the picture. HO and HV stages are just designed too close to nominal to do that IMO.

This may be a dumb question but I'm curious.
Have you tried removing the high voltage winding (physically) and running the set without the winding to see if the current rises after a few minutes? On most failed flybacks I have encountered, the secondary breaks down and burns up. This could leave the primary and the pulse windings intact (could I say).
If this is the case, trying just the high voltage winding from another flyback may be the cure.
I "hot rodded" a Magnavox solid state years ago with great results. It died from a shorted (AC hot to chassis) FM tuner which I temporarily connected into the system (stereo and TV all together) and fried the TV and preamplifier.
My two cents.....
I am sorry to hear of the flybacks demise.

I've had success with bad flybacks by doing the following. Remove the high voltage winding, leaving only the primary windings. Fire up the set. If everything appears to work (other than no HV, of course), get a solid state HV tripler of the type used in later color sets. Connect it to the Hor. Output plate and the chassis to produce the HV.

Might not work on your set, but it is an easy and cheap fix if it does, until you can find a replacement flyback (or talk John Folsom into winding one for you!)

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

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.

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.

Possible FBX Solution
 

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?

Holy Cow! What a nice looking coil winding machine. From the photo that looks like a precision engineered piece - something seldom seen in todays disposable marketplace.
I knew an old EE who was also a ham radio operator par excellence - a master radio craftsman - he would wind his own transformers and coils - by hand! I'll bet he would have really enjoyed that winder in his shack.

I think we have to face the fact that at some point every component will fail, will there be any Flybacks that will work when they are 100 years old? It seems doubtful even under ideal conditions.

Ultimately collectors/restorers are going to have to learn to rebuild, repair and even fabricate unobtainable parts.

Some sets are worth the cost of doing so now, others may be in the future.

Interesting to note this coil winder came out of RCA's Lancaster PA CRT plant when it closed some years back. I is quite a fabulous piece of engineering. But even having the machine is only part of the solution. The original flybacks used magnet wire with special servings (coatings), sometimes made of silk, cotton,celanese, nylon or other materials. It is very hard to find any of these wire types these days. I have been able to acquire some "gripeze" magnet wire. This is enamel coated magnet wire with a special very fine abrasive coating, designed to make the wire have a higher coefficient of friction, so the wires will hold together better on the coil as it winds.
Gripeze magnet wire is still made by the Bridgeport Insulated Wire Co. Surplus Sales of Nebraska has some celanese served magnet wire.

If anyone knows of any other sources for any of these other wire types, I would like to know about it. Thanks.

These guys carry bond wire. http://www.wiretron.com/magnet.html

Litz wire probably isn't appropriate, but it comes covered.

Dissolving rosin in alcohol and brushing it on as you wind is supposed to work also.

John

Does that coil winder machine do that zig-zag diamond shaped pattern with the wire when winding the coil? /\/\/\/\/\/\/\ Supposedly that pattern makes for lower stray capacitance. And is nearly impossible to do by hand.

Yep, the universal coil winding machine does the ziz-zag pattern ,and it IS impossible to do by hand. Here is a photo of the gears , cams, and other items used to set up the machine for a particular winding pattern. The gears range from 19 to 120 teeth, and the heart-shaped cams range from .082" to 1.5" (coil width) . The gears and cams used for a setup is dictated by the coil form diameter, the winding width, and the wire gauge.

John, how do you know how many turns between tap, and gauges of wire to use? do you need to take one apart or are there specs to be found.

btw, you going to fawg this weekend?

All I have to add is:

I hope the set will be running again. The picture you provided of it was beautiful.

I love old electronics. I want to keep it all going for as long as I can.

Someone here said that the minute we expire, someone will let it all go for the price of copper. Maybe. In the meantime, its still mine and I am the caretaker.

Best of luck rewinding the flyback, Mr Folsom. That's one beautiful coil winder!

Bruce

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.