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Old 10-24-2010, 02:18 PM
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Tomcomm Tomcomm is offline
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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

Last edited by Tomcomm; 10-26-2015 at 01:43 PM.
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Old 10-24-2010, 04:08 PM
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miniman82 miniman82 is offline
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'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...
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Old 10-24-2010, 04:42 PM
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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
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Old 10-24-2010, 05:43 PM
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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
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Old 10-24-2010, 09:09 PM
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miniman82, are you talking about HOT cathode current or current at the HV fuse?
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Old 10-24-2010, 09:54 PM
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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.
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Old 10-25-2010, 12:39 AM
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Yeah, but the way I read it, I think that is what he was measuring. I could be wrong.
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Old 10-25-2010, 02:22 PM
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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??

Last edited by Tomcomm; 10-25-2010 at 02:44 PM.
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Old 10-25-2010, 02:36 PM
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kx250rider kx250rider is offline
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Quote:
Originally Posted by Tomcomm View Post
The first replier to my thread seems to considers 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
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Old 10-25-2010, 06:26 PM
JB5pro JB5pro is offline
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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.
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Old 10-25-2010, 07:30 PM
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Pete Deksnis Pete Deksnis is offline
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Quote:
Originally Posted by Tomcomm View Post
My only “experiment” with the CTC2B’s power supply was the replacement of the big selenium rectifiers with small silicon power diodes. ... How many members performed this same “experiment” on their sets??
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
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Old 10-25-2010, 07:41 PM
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Tomcomm Tomcomm is offline
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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.
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Old 10-25-2010, 08:02 PM
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Eric H Eric H is offline
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Quote:
Originally Posted by JB5pro View Post
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?
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Old 10-25-2010, 08:53 PM
ctc17 ctc17 is offline
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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.
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Old 10-25-2010, 09:32 PM
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Quote:
Originally Posted by Tomcomm View Post
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.
I don't care either way, but I think the criticism stems from when you were running the HV way over spec for a long time. These old flybacks need to be treated very carefully, and run as conservatively as possible to help extend their lives. Failure rates increase exponentially with increased temperature, or when running above the correct voltage. I usually like to make sure the B+ is at, or a little below spec. They may have been able to take 10-20% over normal when they were new, but after 55 years, you don't want to push things. I've found that that last 10% can make a huge difference in temperature.
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