RCA 21CT55 B8802897 is Alive!

[roundscreen]

Originally Posted by Tomcomm

ED............When I first got the 21CT55 activated over a year ago, I had no way of setting the Ultor HV without a HV probe on my VTVM. I assumed the RCA engineers designed the HV portion of the CTC2B chassis to limit the HV control range to max spec for the 21AXP22 crt, somewhat above the 25KV recommended in the service manuals.Typical of my approach to design, I went for the max and left it there. Since I converted to the 21FBP22 in "64, rated at 27.5K to increase brightness, I saw no reason not to continue operating at max HV. The focus was in range and I got good convergence. Hey, it made great pictures didn't it?

Only last week when I hobbled-up a 100 to 1 HV probe and carefully calibrated it was I horrified to read 34KV Ultor or 6.5KV above RCA max spec! I immediately reduced the HV to 25KV and the screen looked terrible. I got it refocused but the convergence was way off. I then set HV to 28KV and the picture was somewhat better but convergence was still bad. Rather than getting into re convergence I simply returned HV to 34KV and posted this thread to get some expert advice. Maybe my junky HV probe is way off, but until I get a reading from a known commercial HV voltmeter I'm not going to go off screaming and mess up something that's working exceptionally well for over a year...Tom

Hi Tom
Your set does have a exceptional picture and I am sorry if I sounded insulting.
It is just so dangerous running a vintage tv set with the hi voltage set to high. Why mess around with x rays if you don't have to.
Also I take it that you have not had any problems with the crt arcing inside the neck?
When you find a probe and get the time, Set the hv to 25 kv with a black screen and re converge the crt. Vintage tv repair/collectors are hard to find.
Ed

[KentTeffeteller]

We now have a middle of the run example of the 21CT55. Was under RCA Service Company Contract till the end of the real RCA. Still in excellent operating order. Use it once or twice a week with a Zenith DTV converter box, makes very nice pictures. Not quite to your level but very nice. Very fine CRT, a new rebuilt Colorama from 1967. Was an East Tennessee set from new, a White Lily Flour Executive here in Knoxville, TN bought it new and it was his main set until he died in 1999. His daughter gave it to us afterwards knowing we would keep it maintained and occasionally used. Console cabinet also is nice unrestored original. Sold new at Proffitt's Department Stores new in Knoxville. Area department store founded in Maryville, TN (I remember them back in the day and my mom and grandmother knew D.W. Proffitt, it's founder).

[andy]

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[Tomcomm]

Kent T and Dave A joined the short list of professed 21CT55 "caretakers" which include John T, Steve K, Bob G, Tom S and Steve M, the one at the Early TV Museum? All have already or are about to completely restore these rare RCA second production models to original condition, operating to original RCA specification. The obvious exception is Tom S since I have no intentions of restoring mine to original. I have no cabinet or 21AXP22 CRT, only the front panel, the CTC2B chassis and two 21FBP22 CRTs.

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 2CT2B 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 Ultar 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 ruining 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...0TV/?start=all[/

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. Tom

[Dave A]

I guess I should jump in here with my 21CT55. It is on Steve's list but not identified as mine. Steve, permission granted.

And pix will follow. Serial #BB8801607.

I picked it up about 6 years ago at Rochester from a guy that walked up to me and asked if I wanted to buy an old color tv. Sure I said. I took a trip to his house and there it was...running. Sold for $300. I got it home and was amazed at the picture. It was soaking in color, good registration, and good convergence. The CRT is strong and original. He said it came from the home of the local RCA distributor.

But something was wrong. The color was not quite right. Turn out that either the I or Q was missing. I forget which. The pic was very orangeish. And the recap was needed.

It sat for a while in line for work. From there it took a loooong road trip to Chuck A, John Folsom and some Pony Express help from Cliff Benham. Caps, chokes, etc. done. No room here at the house for a real shop. When I gave it to Chuck, I pulled the magnet, purity ring, and yoke so he could use the yoke. I marked all of the positions on the tube neck with a Sharpie. On re-assembly, it came back as close as anyone could wish for.

On the return it had to go to storage with the cabinet as my work for the World Champion Phillies got in the way.

I retrieved it about a month ago and put it in the living room for assembly. When I did get it back in place, it worked! But it is in need of adjustment from all the changes. I can get a pic but the horizontal is slightly off and not stable. The red seems low and I have to go after that. HV is rock stable and no blooming in sight. A new problem jumped up a few days ago. On power up, the pic is good for a bit and then drops to a smear of video.

Nothing is easy about this but it lives next to my CT100 (currently at Pete Dexnis for work and comparison for his efforts) and my Philco TV123 that needs two doorknob caps. A lot of history in my living room. And a lot of furniture to walk around.

I thought I had some pix from the arrival but I cannot find them in this computer. I will try to edit this post to show the current condition such as it is.

Another survivor,

Dave A

[bgadow]

Dave, you are blessed...I am particularly envious of the Philco. I'd rather have one than a CT100, believe it or not.

[Dave A]

Bryan,

The TV-123 saga is the best story of the bunch. Of the six listed on Steve's site, I have had possesion of three of them. There are one or two others suspected to exist but no one can confirm them.

My first came from a retired Philco engineer who sold me a CT100 ten years ago. It was rough and I kept the chassis, CRT and sold the cabinet...the one that ended up missing at the refinishers as I remember from previous posts. He also had a 123 on his sun porch which was a greenhouse for his orchids. Whatta veneer wreck. I pulled the chassis and still have it for parts. The cabinet was beyond saving with the dampness on the porch. I took it out of charity and did not know what I had. Set #1.

Another local RCA engineer was selling his and I got it about 5 years ago. He had worked for Philco early on and got it there. He had a spare chassis also that is not included in Steve's count. The chassis' were different in that one had a beefed up rectifier on a add-on chassis. This set went to another AK collector. Set #2.

I sent that one on and it was replaced by the 123 that Chuck A documented a while back on AK. It had been a prize on a national game show and was/is in great condition. Chuck did the recap and it now awaits two small doorknobs. The big one failed and that was replaced. Now one of the others is gone and I need to get both to do it right. Any doorknob collectors out there?

It is a cantankerous beast and very hard to set gains/backgrounds to get a good pic. Set #3.

The odd thing about my 21CT55 is my mindset about it when it came back. I just threw it together and powered up and it worked. It was no different to me than a CTC7 in my mind. Just another 21" color set when you look at it from the front. I had to step back and remind myself that this is a jeeped-up CT100 and should need tender loving care to do anything at all. It lit up and now I have some work to finish. I would be curious to see how this second generation fits in with Pete's efforts on V1.0. No pressure Pete!

Stay tuned and if you are near SE PA, stop in for the tour.

[John Folsom]

I want to thank Dave A for allowing me to be the new custodian of his excess Philco 123. It is a bit scruffy, but it came with a spare chassis, so I am very much looking forward to restoring it.... one of these days.

[Pete Deksnis]

Originally Posted by Dave A

A new problem jumped up a few days ago. On power up, the pic is good for a bit and then drops to a smear of video.

Dave A

Hey John Folsom: sounds just like a certain CT-100 in France, oui?

[Pete Deksnis]

Originally Posted by John Folsom

...I am very much looking forward to restoring it.... one of these days.

What is it with these rare Philco's? None of them glow properly. I've been sitting on a set of restoration caps since September 2005...

Don't know how Tom's thread got on the TV-123, but they are different in that there's not much RCA influence when you check the schematic. Also, the shallow chassis is a pain to work on; just ask Chuck. Nice nonetheless to have one. BTW, as the caretakers know, TV-123 is the chassis designation; 22D5102 is the model number of the most prolific unit, a VHF-UHF mahogany model.

[Tomcomm]

My reactivated 21CT55 has been operational for over 18 months with no problems except.......it takes about 30 minutes for the screen to reach acceptable size and convergence after cold morning power start up. It takes an additional 60 minutes to reach near perfect vertical linearity and final convergence suitable for critical picture capture.

I use the Digital Video Essentials' crosshatch with circles pattern to evaluate this problem with black felt pen dots on the CRT screen after the sets been running about three hours. The dots give a very good indication of circle size and linearity. A few pen lines indicate where convergence is less then perfect. Results have been consistent the last three mornings so what components has a 90 minute thermal time constant? I've already replaced the tubes and at least five capacitors in the vertical osc/amp circuitry and always keep the B++ buss set for 410v with my AC input Powerstat. Boost stays at +880v and the ultor runs about 30KV.

Hey, I'm not overly concerned and can live with the long warm up. It's not a
restored show item, just a hobby toy. Any comment or suggested fix is welcomed......Tom

[zenithfan1]

Might want to check for wandering resistors. I've had a few sets that had vertical problems similar to yours, I've also had some that creep in as the set warms up. Use some freeze spray on suspect resistors and caps after the 90 min. warm-up, watch for a fast change in the picture where your dots are. Good luck with her, you have a great set!

[ohohyodafarted]

Hey Tom,

I am having similar issues on my 55'. Warm up is slow. By that I mean from a cold dead start, convergence is WAY out, by about 1/2". As the voltages stabilize, convergence comes in very nicely. It takes a good 15 minutes from cold. Shut it down for a minute and you are back to way out again, but will come back into coinvergence faster if the set has been previously warmed up.

My linearity is very good, and HV regulates nicely at the 25KV spec. I too am running on a variac, at around 110vac, which gives me a spot on 400vdc B+ If I run off of 120 line voltage I get 437 vdc B+ and my flyback runs 20 degrees hotter. I already toasted the origanal, so I am being most carefull to not destroy this one. Running at 400vdc the flyback operates at about 125 degrees F after several hours of run time and also with the dog house panels removed. After I have the thing running to my satisfaction, I will reinstall the dog house panels and install a muffin fan to keep the dog house internals cool.

I would be interested in knowing what your flyback temp is after you run for several hours, just for comparison sake. I use a DMM with a thermister probe to take temp readings. I of course do it with the set turned off and the door knobs discharged. I place the probe on the surface of the primary windings and hold it there till the temp reading stabilizes. I like 125 degrees F. It seems to me to be a safe operating temp.

Been trying to run down an intermitant flashing brightness issue, but haven't had much time to trouble shoot lately. I am pretty sure if I stick at it long enough I will locate the gremlins. that is, if I live long enough :-)

I like Mark's suggestion to try freeze spray on resistors to see if I can cause the convergence to drift out. Maybe I can find a resistor that is overheating and changing value as the set warms up. Being as convergence is done with the set warmed up, it would be logical that when the set cools down it would be out of convergence if a resistor is changing value as it heat up. I just ordered up 3 cans of freeze spray. I found it online for only 4.99/can at http://www.southernhillscomputer.com/index.html some places wanted $10 per can. The stuff is R134a refrigerant. I am epa licensed to do refrigeration repair and buy this stuff in 30 pound drums normally for repairing air conditioning systems, but 30 pound drums are a bit to large for squirting resistors with :-)

Bob

[kx250rider]

Have you replaced the selenium rectifiers and checked all the filter caps? Although I haven't personally had trouble with those huge seleniums in the CT-100/21CT55, I know they're capable of trouble like you're having. Fairly simple power supply. However, it might be a benefit to have that ultra-slow warmup... I think most failures of other parts happen on startup surge; when the B+ is highest (in solid state rectified sets like this), and the tube filaments are still cold and the power supply is running hog-wild unloaded. Come to think of it, maybe let it be, as long as it isn't a slow-forming filter cap which may be pulling a ton of current. An AC ammeter would check that too.

Charles

[ohohyodafarted]

Yep, power supply is all reworked. Seleniums are just ther for show now. Every can in the set has been re-stuffed with bran new axial lead caps.

I have monitored voltages during the warm up, but I do not find any significant variation during the period that it takes the convergence to stabilize.

Steve Kissinger saw it and said the he dosent have this symptom on his recapped 55' . I could live with it but it is a symptom I don't like when I wish to turn the set on for a few minutes to demo it to someone. It would be nice for convergence to come up right away so the picture would be watchable in a reasonable amount of time.

I even re-hooked up the old seleniums just to see what would happen. I got a very substandard 372vdc when opperating at 120vac line. The set runs much better on the silicon diodes, so I am convinced that the old seleniums cause sub par performance.

Bob