RCA CTC4B "Gainsborough" picked up in San Francisco
 

After receiving a much-appreciated tip from another collector, I was able to bring home this 21CT664U set last night. It is missing the back, and the CRT is broken :tears: but the cabinet is in excellent condition, except for a drink stain and a couple of thin scratches on the top. The chassis is also nice and clean other than normal dust accumulation. The CRT "was" a 21AXP22A with the code 6048 on its connector, so I am guessing it was replaced after maybe five years of use. So, now I need to start a hunt for a good one.


http://70.36.238.5/ctc4b/IMG_2070small.jpg

http://70.36.238.5/ctc4b/IMG_2071small.jpg

http://70.36.238.5/ctc4b/IMG_2067small.jpg

http://70.36.238.5/ctc4b/IMG_2065small.jpg

Hey Chris, glad you got that! I got a tip on that yesterday, but I just couldn't see driving almost two hours to take a risk on something that was already out on the curb for free with no contact info. Noticed the ad was taken down fast... I had my fingers crossed it wasn't a tanker.... or worse, that person who makes the cat condos with the little dangling catnip mouse.

Way to go!

Nice find! Rare model.

-Steve D.

vary nice , too bad about the crt .

That cabinet looks to be in excellent condition. Nice save!

Beautiful set!

If you look in through the neck with a flashlight, you may find the gun assembly embedded into the shadow mask. Looks like it may have been launched forward when the neck snapped.

Ooh, nice! If you run across a stash of good 21AXP22s, let me know :)

Meanwhile, it looks like my adapted 21FJP22 will work, although I still haven't done any of the color setup, and have various other loose ends to tie up in my CTC-4 restoration.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Probably did that while moving it to the curb.

Yah, it sucks to think it may have survived sitting all these years, and then got
broken just recently..... But anyway it is a nice looking set, keep yer fingers
crossed a picture tube will come from somewhere to you...... Good Luck...

Nice set

I hate that when you can see the after-effect of the gun assembly going thru the shadow mask.

Congratulations on a wonderful find!! Hope you can find a good 21AX, but if not, you can drop a 21CY, or a 21FB into the mask and set that up. Need to be sure that the anode connection doesn't arc to the yoke flange, otherwise, a relatively easy install.
Good Luck!!
Kevin

Thank you all for the nice comments, and for the suggestions about all-glass CRT substitution. The cabinet is in such nice condition, I kept looking at the back edges and elsewhere to see if it had been refinished-but it has not!

Regarding CRT substitution, the CTC4's yoke mount is interesting-it appears to be just about held in air by three metal rods that go to cabinet anchor points above and below the CRT near its front. That seems to me to potentially allow a glass CRT to be attached somehow to the front of the cabinet without needing to clamp the yoke onto the new CRT, which would be a big challenge otherwise. In fact, I also have a CTC-5 that may need a glass CRT as well, and I am going to look at similar mounting options for that set's yoke and CRT.

Glass tube conversion with pics

http://www.videokarma.org/showthread.php?t=253870

This article describes how I converted my CTC-4 to use a glass CRT:

http://antiqueradio.org/RCACTC-4ColorTelevision.htm

It's not very difficult.

The article isn't finished (nor is the restoration), so I haven't hooked it up to the rest of my website.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Phil's comprehensive article on converting glass to metal CRT's is probably the way to go. Just for reference I thought I'd post a photo of my CTC-5 Wingate with the RCA metal to glass CRT conversion kit. When I purchased the Wingate many years ago it already had the conversion kit installed. The previous owner had converted the original 21AX to a 21GUP22. I personally have never seen one of these RCA factory conversion kits offered on Ebay or any other source. The kit has a large diameter metal ring with welded attachments at 11-1 o'clock & 5-7 o'clock positions that screw into the existing CTC-5 mask to hold the tube in place as seen in the photos.

-Steve D.

There is no good way to attach the CRT to the face plate of the set, and keep it easily revertable to original. Use Phill's method, and don't re-install the plastic shield...Also I have been able to get away with sandwiching plastic between the metal yoke mount and the HV button to prevent arcing instead of cutting the yoke ring...

Mstaton-

Thank you for posting that topic link, including your pictures. I know I had read it before, but I forgot it. That will be a big help.

Phil-
Thanks for posting the link to your CTC-4 page. I will read it as well.

Steve-

Thanks for posting your Wingate pictures with the RCA conversion kit, it is nice to see the "official" way it was done.

Tom-

I appreciate your notes and comments, I will look at Phil's notes too.

Some time ago, I picked up a used 21FJP22 along with its mounting hardware from a late-model RCA set (CTC-16 or 20) that my be part of what I can use, if I am lucky.

Phil, I read your description of installing an all-glass CRT in your CTC-4. You almost make it sound easy! I appreciate the detail that you put into your restoration description.

Part of the high cost of these early color sets were all the mounting and safety precautions needed. Once they went to glass tubes they were able to simplify to a degree the whole process. Still they found a way to get the job done.

I recently decided to proceed with the restoration of this CTC-4. It needed a bunch of tubes, the usual complete replacement of wax/paper and electrolytic capacitors, and a few resistors (oddly, all low-value ones that had drifted higher; none of the high-value ones tested bad). I connected it to my Sylvania test jig with a Variac and ammeter, and it had a raster on first power-up, woo hoo!

Initially, I got no signal through it, but with a few tests using a Sencore VA62, I found it had a bad video detector diode. That diode was already a replacement; since Phil Nelson also had a bad one in his CTC-4, I wonder if these sets are hard on those diodes. With the diode replaced, I get a pretty good signal through the RF input:

http://70.36.238.5/ctc4b/IMG_2990small.jpg

I started testing the UHF tuner using the VA62's output, which can be set to any channel up to 83, and found variations in performance among several 6AF4 UHF oscillator tubes. With a new RCA tube in place, UHF works well all the way to the top of the band, amazing to me for a consumer product sold in the mid-1950s.

Now for the bad news: I decided to go through the horizontal alignment procedure from the Sams Photofact folder, which includes adjusting the horizontal waveshaping and horizontal hold/frequency coils, followed by the HV and linearity adjustments. Well, I did the waveform adjustments and everything seemed fine, then as I got ready to connect my high-voltage meter, I saw a big, bright arc inside the HV box, almost like a fire had started in there! I pulled the plug quickly, and after a minute or two to let my heart calm down, I looked at the flyback and felt it; it was pretty warm, and most of the rubber "tire" coating had sagged down, exposing the top where the arc went to the top of the HV box:

http://70.36.238.5/ctc4b/IMG_3021small.jpg

http://70.36.238.5/ctc4b/IMG_3026small.jpg

(The sagging is to the left in the first picture, which was taken with the chassis flat; normally, it is vertical.) You can see where the wax has drooped low enough to completely expose part of the coil on the lower-left part of the "tire" in that picture.

Before I saw the wax damage, I powered up the chassis after everything cooled down, and as soon as the HV came up, the arcing started again, so I pulled the plug quickly of course.

Apparently, the "waveform adjustment" procedure, which has steps such as "turn the coil until the slug is all the way out, then bring it back" (putting the horizontal frequency way off for a few moments), caused the flyback to get warm enough to start melting the wax, and I did not think to watch it or otherwise be concerned, until the arcing happened. Aside from hating myself for messing up a part that was fine for 50+ years, my next step will be to remove the wax and inspect the arc spot for damage, to see if I can just apply a bit of corona dope there, then cover the whole tire with sensor-safe RTV silicone and hope for the best. If I remember right, the picture was still on the screen even when the arcing first happened, so I hope that means the flyback may still be OK once re-insulated. I tested its resistance from the H output tube cap to the HV rectifier tube cap, and got 490+ ohms (versus 510 ohms on the Sams schematic), so it is not open but could that be a sign of some shorted turns?

The remainder of the horizontal adjustment procedure is to set the high voltage, and adjust the horizontal linearity for minimum current to the yoke. So, there is no step to check the H output cathode current, but should I measure it anyway, and possibly re-adjust the waveshaping coil while monitoring that current (as well as my oscilloscope), if in fact the chassis seems to work again OK once finish the flyback repair?

This is why I always use the utmost of caution when working around the horizontal section of these sets, if you fry the flyback it's impossible to find another one. That means you'll probably end up using a completely different flyback if the one you have can't be repaired.

It's not coated in rubber BTW, it's wax. I just repaired a flyback from another set by replacing the wax, see my thread on the Gilfillan prototype. Use extreme caution around the tiny wires of the HV winding, too much heat can melt them. I used a soldering iron to carefully melt the old wax off, then used a silicone mold to cast the new section from a negative of what was still there of the old section. Electronics safe RTV works too, I was trying to go for originality because my flyback has a rectifier string around the outside of the tire. You could also put a piece of phenolic over the metal section of the cage it arced to, that would help keep any stray HV to a minimum.

Good luck, it's not an easy job.

I would find it strange for the fb to be destroyed from a short use with one of the
shape coil not properly adjusted. I would put more stock into either there is
something wrong with the part, as your resistance readings possibly indicate, or,
too much current through it.... Was Horiz Output Tube cathode current within spec..?
Also, if the resistance was off, I would imagine cathode current would also be off....

If you can pull off a fix for the arcing, I would check cathode current, and the grid
voltage, too far positive and it's going to gobble up too much current. And look
at the shape of it signal, no dc leaking in either....

So is that flyback completely unavailable....?

Good Luck !

.

Only source is other chassis, no one made 'aftermarket' ones.

Adjust the horizontal linearity for minimum H Out Tube cathode current....If that is miss-adjusted you could be cooking the flyback.

My CTC7 had the same problem, it had a hole burned through the rubber insulation where it arced to the metal cage, luckily I found it before it was fired up.

I was able to remove the covering, clean the burnt area and recoat it with some low acid RTV and it works fine. As long as it hasn't burned through the wires it should work on yours.
A dab of High Dielectric Epoxy paint on the area before coating it might not hurt either, I didn't do that but mine wasn't burned much at all other than the cover.

..as well as the H. output tube.

Great Find!!!!!!!! Sad about the necked CRT. But fear not, one will turn up at some point. I guess I am something of a purist. My feeling is that the most important reason for having a CTC4 is to have the 21AXP22 crt in a functioning set. That original crt is in large part, what makes the set rather historic. The 21CT55 was the only earlier set to use the 21AX. The first mass use of the 21AX occurs in the CTC4 series. (some clones of limited production numbers were sold by other manufacturers in very small quantities).

The original CTC4 flybacks are prone to failure. ManyMany were replaced with an improved version. The original flyback is part #110409 (drawing #1106237-1). The improved replacement flyback is 101959-A and also involves a number of circuit changes to the chassis which RCA made to accommodate the new flyback design. According to the drawing # stamped on your flyback (1106237-2) you have a replacement flyback in your set. There should also be a paper hang tag inside your set explaining that you have a replacement version flyback and that the chassis has circuit changes to accommodate that replacement flyback.

When you start to work on the chassis you are going to find a number of circuit changes which will not match the original RCA schematic. Those changes are on a paper hang tag that should be attached to your set (provided some numb skull didn't pull the tag off and discard it.) (there are instructions on the tag that tell the service tech to attach the tag to the inside of the set after installation of the replacement flyback)

I believe someone here on VK (possibly Nick?) posted a photo of the hang tag at some time in the past which has all the circuit changes that have been made to your chassis.

You have a Wonderful old color set there, and it is quite an uncommon model. According to my RCA service bulletin, the Gainsborough came in Walnut or Maple finish. Which is yours? Hard to tell in the photos. Looks like Walnut to me.

My Cheltenham is in natural Birch finish But over the years the color has mellowed and it looks more like Pine now. I just completed the re-finishing of my CTC4 Cheltenham cabinet, and I am about to start the re-cap of the chassis.

I think my CTC-4 thread has pics of the hang tag in it, if not I can email them to anyone in need.

Thank you all for the helpful information and comments.

Nick, I may put a piece of phenolic on the top surface of the HV box if/when I get this set going OK again; does "fish paper" accomplish the same thing, if I find some of that instead?

Username1, Tom, and Old Coot, I will go ahead and put a current meter on the H output cathode when I am ready to fire this set up again; also, I will run the Variac low to start, and observe the results of adjustments I make. The adjustment procedure for a CTC-4 does not specifically address the cathode current, but I will do so anyway.

Eric, my thought was to use some corona dope on any suspicious windings in the arc area once I have the wax carefully removed (and before I coat it with the silicone). Do you think it is a viable alternative to epoxy paint?

Bob, this set has a CTC-4B chassis, and seems to match the "late production" schematic diagram in the RCA 1955-1966 Field Service Guide. I thought I saw an RCA note that said all Gainsboroughs were "late production" models and were built with the changes in place; there is a list of them in the Guide that I will look at and compare with my set. There is no hang tag or any other service information in the cabinet or chassis. This is a maple-cabinet set, I think; it is a much lighter color than any walnut wood I have seen. Indeed, I would love to put a 21AXP22 back into it one day. The broken CRT was a 21AXP22A with the date code 6048, and from various tube date codes, this set was likely in regular use to perhaps 1966 or so.

We're talking 24kv+, I don't think paper is gonna cut it. You need something thick with high dielectric strength like phenolic, nylon, plastic, ect. FWIW, once you fix the obviously high horizontal current situation I doubt you'll have the issue crop up again. It happened because the insulating wax melted away, allowing the HV to find the path of least resistance.

I was gonna say the same thing re. fishpaper. It's useful in lower-voltage applications, but I sure wouldn't use it here.

I used some of this 90KV-rated cambric tape when transplanting a glass CRT into my CTC-4. I still have much of the 20-yard roll left. Send me a PM and I'll mail you some to insulate that spot where the arcing occurred.

http://antiqueradio.org/art/RCACTC-4...latingTape.jpg

I would reserve judgment on the flyback until you can remove the wax and carefully inspect the winding.

Apart from this little incident, if you're getting a good picture from RF input, that sounds like great progress.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Chris,

Just goes to show you learn something new every day. I had always wondered about the 3 different CTC4 chassis. I did some investigating and in one of my RCA service bulletins I found a chart defining the 3 different chassis. The 21ct660u and 661u in the two low end Seville and Haviland models, used the early production CTC4 chassis. The 21ct662u Director, used the CTC4A. The 21ct663u Cheltenham and 21ct664u Gainsborough used the CTC4B.

There are a fair number of circuit differences, mostly in the color circuits, between the CTC4 and CTC4a. I don't have a CTC4B RCA schematic so I am not sure where the circuit differences lie in the CTC4B version.

Unfortunately I got my Cheltenham without a chassis. It was just a gutted cabinet. I have a CTC4 and CTC4a chassis to work with but I do not have a "B" version. And what is worse, the CTC4A I have has been canabilized so I am not certain which direction I will proceed. I am leaning toward rebuilding the "A" chassis but that will entail finding a pile of spare parts that are missing. Clearly the CTC4 early version is not correct for a Cheltenham.

Nick and Old Coot, thank youfor the comments regarding fish paper. I just had no idea of its properties.

Phil, thank you for the tape offer. I will get in contact with you once I evaluate the flyback. As Nick said, reasonably it should not come up again; it would be more of a "just in case" plan but still maybe worthwhile. And, I will likely want to use some of that kind of tape for the CRT HV connector as well, once I am ready to install the chassis into the cabinet.

Bob, I wish you luck with that Cheltenham restoration (maybe, reconstruction is more like it), I know you are a person who can definitely succeed with the project. If I can help with identifying details of the CTC-4B chassis, I will be happy to do so. At the least, I could take and forward lots of high-resolution pictures from various places and angles. My chassis had very little work done other than tubes over its likely ten years in use; I only identified a couple of obviously-replaced capacitors plus the video detector.

Today, I had both a funeral and a banquet to attend, so I only have had time to get online a bit, but tomorrow I hope to evaluate the flyback and post an update.

Here is the location of the arcing, after cleaning most of the wax from the flyback HV coil.

http://70.36.238.5/ctc4b/IMG_3036cropped.jpg

The view in this picture is about 5/8 inch wide, with the darkened area being just over 1/4 inch long. My main concern would be whether the dark parts are now carbon or something else that I should attempt to remove, before applying some corona dope (or other substance such as HV-rated epoxy as Eric mentioned?), followed by the silicone.

Also, I doubt that I could remove "all" of the wax on the coil, especially after seeing discussions of vacuum-impregnating flyback coils. I would be concerned that the materials or methods to do so could be risky themselves. Is some remaining wax likely to doom the silicone coating integrity as a whole? I appreciate any suggestions here.

Great Picture ! If it were me, I would use a tooth brush, try and clean all that burnt
looking stuff off. Try and determine if there is a lot of damage to the insulation of
each wire.... You may need to treat that, varnish ?

I read the piece on the hot wax and the vacuum pump, really good ! It was mostly to
promote boiling off of moisture. Lower the atmospheric pressure and water boils
off at a lower temperature.... Just as they use a 12 Lb cap on your car radiator, it
increases the boiling point of the coolant.

You have to be sure after you coat it with whatever your going to do, it has no air
pockets, it can over time promote oxidation and corrode and open up a wire....

But it looks to me the wire is in good shape ! clean it coat it,
patch that tire, and back on the road !

:)

.

Thanks. I am carefully using a pin point to remove what I can. Even with a magnifying-lens lamp, I cannot get as good a view as the camera can, but I will try more pictures after some cleaning work.

I'd probably try to clean that spot a bit better. There is no need to Vacuum impregnate the fly with wax, and I think putting silicon on the fly is overkill. What I'd do is heat the portion of the wax tire that fell away (probably with a hair dryer) till it became soft enough to smoosh back on to the fly, do that and mold it back into the shape it should be in. If that proved impossible I'd try making a mold or form around the fly to pour molten wax in to cast a new wax tire.

The wax can always be remade if it fails, but silicone is going to be hard to remove if bad.