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  #16  
Old 07-31-2014, 12:38 PM
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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.

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  #17  
Old 07-31-2014, 01:56 PM
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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...
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  #18  
Old 08-01-2014, 12:40 AM
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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.
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  #19  
Old 08-01-2014, 12:50 AM
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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.
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  #20  
Old 08-02-2014, 01:34 AM
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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.
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  #21  
Old 08-05-2014, 07:17 AM
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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.
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  #22  
Old 01-16-2016, 01:39 AM
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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:



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:





(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?
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  #23  
Old 01-16-2016, 06:09 AM
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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.
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  #24  
Old 01-16-2016, 11:46 AM
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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 !

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  #25  
Old 01-16-2016, 12:25 PM
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Only source is other chassis, no one made 'aftermarket' ones.
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  #26  
Old 01-16-2016, 02:02 PM
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Adjust the horizontal linearity for minimum H Out Tube cathode current....If that is miss-adjusted you could be cooking the flyback.
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  #27  
Old 01-16-2016, 02:28 PM
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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.
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  #28  
Old 01-16-2016, 02:29 PM
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Quote:
Originally Posted by Electronic M View Post
Adjust the horizontal linearity for minimum H Out Tube cathode current....If that is miss-adjusted you could be cooking the flyback.
..as well as the H. output tube.
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  #29  
Old 01-16-2016, 04:10 PM
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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.
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  #30  
Old 01-16-2016, 06:36 PM
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I think my CTC-4 thread has pics of the hang tag in it, if not I can email them to anyone in need.
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