Digging into the CTC-9
 

I picked up a '9 Winslow on Craigslist a few months back:

http://www.videokarma.org/showthread.php?t=246304

As found, it had a pretty bad cataract, and produced a sickly green picture that barely held vertical or horizontal sync. After about two minutes of running, I could see a little bit of smoke coming from the HV cage.

I elected to do a full recap. While 90% of the caps in this set are of the modern type (mostly maroon, but some orange drops as well), about a quarter of them tested leaky on my cap checker. I noticed on those that did not test leaky, that when I went to check their values, that the cap checker eye did not open nearly as much as it normally would for a new cap of the same value. For fun, I took some low ohm resistors (5 and 10 ohms) and put them in series with a new cap and tested it-it tested a lot like the older caps. So while this isn't definitive proof, it certainly looks like the older caps had some high ESR.

No issues with the recap. The set powered up, with no smoking. I next decided to tackle the cataract. The picture tube was a 21fj that tested brand new. Playing the tv now, I could see that it produced an excellent picture. I took it to a friend's shop, and we spent all day Saturday working on the thing. First we tried the hot wire method. Heat would not do anything to this stuff. Even stabbing my soldering gun into some of the gunk we had scraped off of the side did very little to it. This was after preheating the tube, etc. Whatever this PVA was, it wasn't going to come off that way.

The safety glass came off perfectly, as outlined on that great series of Youtube posts. Heat guns and work lights saved the day. Well, for a while. After the tube had cooled, I was wiping down the picture tube face with a paper towel before applying the double sided tape when it imploded. That is to say, I had both hands in contact with the face of tube when it seemingly vanished.

When I opened my eyes (I was wearing safety glasses, luckily) my poor friend was hunched over the hood of a car, obviously in pain. I knew I had to have been hurt, but I ran over to him and we began to assess just how badly we were injured. He had taken a large piece of glass straight into the face-it put a nice slice into his chin and under his nose. My worst cut was a piece had sailed past my head, making a neat slice across the middle of my ear, nearly going all of the way through. Needless to say, things could have been much worse. I got cut in about ten places, and holding the bulky shirt I was wearing up to the light, it looks like it has been blasted by rock salt. The sound was tremendous-even though the garage door was down, it was loud enough to bring the neighbors on all four sides of the house over to investigate. I'd wager it was on the sound level of a quarter stick of dynamite going off-it certainly had my ears ringing for the rest of the day.

So that was a bit of a scary setback-there is a LOT more to that cataract removal story-we tried every possible method to pull that thing off without going to the heatgun method, but that would be just too much to write here. After all, there is a tv that needs attention here....

Holy crap! I'm glad no one lost an eye or got killed, that glass could have easily gone into either or both of your necks. WOW! I will be seriously re-thinking using the heat gun method. I think it gets the face too hot while the rest is much cooler in comparison. That is a very bad thing, IMO. These tubes can cook in an oven at the tube re-builder but the whole thing is one even temp then, so the stress of expansion and contraction is even with the whole thing. That's my theory anyway. That's a pretty cabinet on that set BTW. I do believe it's a blonde Anniversary model, the Winslow is kinda french provincial. I have the Anniversary right here next to me in Mahogany, same exact cabinet. The blonde is gorgeous on this model I think. Good luck on getting another CRT, too bad a good one imploded.

We can restore them together as we're about at the same point. I have a lot of work to do on my cabinet though, printed finishes are tricky but I have a plan. Instead of hi-jacking your thread, I'll start my own later:) VERY glad you guys lived to tell the tale.

Ouch!

Thanks for reporting this. I'm sure it'll encourage others to exercise caution.

It's odd that it broke when it did. I assume you were only applying only very light pressure while cleaning up the residue.

John

Maybe it stress fractured and decided to let go when he applied a slight pressure to the face, who knows.

Wow, thank god you guys are OK all things considered and that nobody had serious injuries. This heat gun method seems to have its fair share of dangers and Im starting to advise against it now. I've done some 10+ cataract jobs with success with the heat gun method until I had a 23EGP22 blast into peices in front of my face about 2 years ago, which Im sure most of you remember that disaster. My theory at this point is that the CRT face gets so hot and it starts to expand laterally. The bell of the tube stays cool since its not even heat and it does not expand (like mark pointed out), but when the lens starts to expand, it puts alot of stress at the frit seal and thats probably the weakest link and it fails right there. I could be wrong, I've never conducted stress analysis on a CRT before.

CTC17 had very good luck with the hot wire method on the Zenith tube. The key is keeping enough current going through the wire so that the PVA does not act as a heat sink when you apply the wire, otherwise it stops you dead in your tracks.

As for the sound, I remember exactly what the 23EGP22 sounded like. It was like a bomb, it sent a nice shock wave into the air and it felt like someone punched me in the chest and then there was Phosphor rain for about 30 minutes afterward. It was on a saturday afternoon and my parents were upstairs watching a football game. They both basically screamed out loud wondering what the hell happened and they both ran downstairs to see if I was OK and what happened. The sound was so powerful and intense. Then little phosphor flakes and dust were everywhere and floating in the air and I couldn't believe how far the glass traveled yet amazingly, I was scratch free. I couldn't believe I was OK. The sound of the glass shards striking each other was also incredible. It all happened in microseconds and it was over just like that.

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That's terrifying. Thank your lucky stars that neither of you caught a big piece of glass in the jugular.

I just permanently lost all interest in experimenting with cataract removal. If anybody asks me whether it's a good idea, I'll begin by pointing them to this thread.

Phil Nelson

Man im glad you guys didn't get it worse than it could have been! I hope you can find another CRT! When I did my Ctc 16 a few years back I was worried about the same thing.

I am glad to hear you and your friend are (mostly) OK.

So much for the heat gun method - I wouldn't try it at this point.

It serves as a reminder that CRTs are *dangerous* lest we get too casual in handling them. That much glass going in every direction at that speed can kill.

I was surprised that my hands weren't shredded by the incident. It would appear that they shielded my face from harm. I only had two small cuts in the palm of my right hand-the one that wasn't holding the paper towel.

Judging by the spray pattern the glass made-it looks as if most of the force was directed towards one side-luckily out of our direction. The shadow mask was shredded, I was surprised, it was made of pretty thick metal, like the kind you would need metal shears for. That certainly worked in our favor as well. All that is left now is the gun assembly, and the orphaned safety glass-in case anyone needs a roundie safety glass.

I wished that hot knife method had worked. But this type of pva was not heat sensitive AT ALL. We got the wire deadly hot, and just for the heck of it, blowtorched it just below the melting point, and it still did absolutely nothing to the worklight-softened PVA.

Now, I have another 21fj that is cataract-free. I have that installed already, and I had a miserable picture on it. All but the green gun tested as bad. After letting it cook at 8 volts, the other two guns came up, and now I have a crt that tests largely good, with excellent tracking.

But now I had some arcing in the hv cage, and I could only crank up the hv to just under 20kv....

well hopefully the let is soak in water method may work...

I will get started on that this weekend.

I am wondering you could just pour some PVA on the glass and set the CRT back on it and then let it cure to replace the PVA after a cateract removal. I assume the safty glass lens is no protection at all with out the PVA.

I was thinking of wrapping some packing tape around the perimeter of the lens building a wall then pour in some PVA (white glue I presume) to form a puddle in the middle then puting the CRT in place. Of course the hard part would be to figure out how much glue to pour into the puddle so as to have complete coverage, with out too much over fill causing a huge mess. oh and the last problem would be how to keep the center of the tube from coming into contact with the lens a squeezing out ALL the pva.

perhaps a jig that would support the crt inverted over the lens with just a fraction of an inch separating them during the cure. It sure would be helpfull to know how it was done at the factory.

another option would be to band them if anyone knew how to do that properly.

Stories like this make me worry just a bit about tubes installed with out the safty glass installed.

It is my understanding that only the later round color crts introduced this method of applying the safety glass. So conceivably, a 21fj without its safety glass wouldn't be any less safe than say, a 21ax. That is why early roundies have the pane of safety glass built into the cabinet.

As for how RCA applied their PVA, I found a small injection nozzle fixture on the side of the crt where it appears the PVA went in. It is basically a glorified plastic washer.

I think if I were to ever attempt this again, I would take my crt to a large controlled oven, such as those used for powder coating, and slowly bring the crt up to temp in that, pull the crt, pop off the safety glass, and then run a cooling cycle to bring it down properly. Simply copying the heating cooling protocols from a crt rebuild operation should be a fine guideline.

yea I was not really thinking of roundies when thinking about the banding, I have several caterat rectangle one that have no safty glass in front of them.

so perhaps the factory had a fixture that held them apart and then the pva was just injected in. That does not sound to impossilbe to duplecate.

I can see holding it sideways with the injection port on the bottom and then leaving the top un sealed with tap, fill'r up and then tape off the top side.

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Yikes! It sound like we have all been effectively working back in the pre-OSHA days. I confess to having gone without safety goggles more often than not when handling CRTs. But this thread makes it clear: **it happens. Now I think I'm going to investigate making up a Kevlar suit to go along with the glasses.

+1, Also, trying to replace that PVA would most likely end up having air bubbles trapped in it. Sealing it back on the way andy says works beautiful.

Well, my next step was to mess with the HV. After getting the spare crt installed, I noticed the HV was normal, but I noticed that I couldn't advance the HV beyond 20kv. The picture looked a bit out of focus as well.

The next day was a bit more humid, and on power up, I heard some spitting coming from the cage. Opening up the cage while under power showed some nice corona all around the 6BK4 cap and lead in. The rubber on the wire was all dried out, and the cap was very crumbly.

Well, the Zenith roundie had provided a good crt, why not some HV hardware, too? I pulled the RCA's lucite HV cup, too-as it was warped. Surprisingly, the Zenith's HV cup went right in-they were a perfect match! While the RCA's 6BK4 cap was like any other tube cap, the Zenith's is a massive insulated sleeve that covers the whole top half of the tube. The wire lead is also heavily insulated. With those in, I could ramp up the HV to just under 40 KV! Not that I kept it there.

Now I have a pretty well-functioning roundie. I can now dig into convergence and color balance. Any tips on these settings? What should HV be set to? Can I damage the crt by cranking up the Drive/G2 controls too high?

One could always use something like RTV615 which will not age and does a nearly perfect match of the index of refraction of the glass. This will eliminate the reflections that you get without the PVA and prevent any fogging over time. It will also give you some added protection. But, it's very expensive which is probably why they went with PVA even though they must have known that there would be an eventual problem with microbial action and evaporation.

My understanding is the PVA layer is what makes the glass safty glass.

without it you just have more glass breaking and flying around. Perhaps I am all wrong on this but I thought that is how saftey glass was made (two layers of glass with a bonded memebrane that keeps the glass from shattering.

The HV should be set at 25Kv, and yes, you can damage the tube by turning the controls up too high. If you see retrace lines, back it off until they disappear and then just a hair more. The set ups for it should be outlined in the sams folder.

It makes a lot of sense that the multiple layers are important... but isn't the bonding substance used PVB rather than PVA?

http://en.wikipedia.org/wiki/Polyvinyl_butyral

jr

That is correct. But, when done the way we've been taking about, it is basically going back to the "picture window" type of safety glass, only curved to fit the screen instead of being further away. It's better than what's on my avatar Zenith, NO safety glass at all. I'm looking for the correct lens with the gasket. The 21FBP22 was an unbonded tube and uses the curved glass with an air gap like after a cataract surgery on a FJP but with the gasket rather than the double face tape. (preferably 3M automotive tape) I think it is safe.

I ask about developing issues with the crt because of overdriven controls because the SAMS is not very specific-calling for 23.5 kv and the schematic giving a range of 15.5-21kv.

Which controls for gun color balance would be the deadliest to overdrive? G1 (background) or G2 (screen).

My final question is that this set originally had a 21cyp22 in it. Are there any mods or considerations that need to be taken in for the 21fj that is currently installed in it?

Yes, there are a few slight mods but I can't remember off the top of my head. My set is modified already and right before I put it "right" I realized that it's because of the 21FBP that's in it now. You said the set had a FJP, the mods have probably been done already. Can you please take a picture of how the screen and grids are hooked to the chassis? That's what is modified, if it looks like mine, you should be good. A few of the wires go to new positions on the resistors there at the terminal strips. The screen controls are the ones you have to be careful with, they are the ones I was referring to about the retrace lines. I'll look at my sams when I get home about the Hv and post anything I find useful. Hope this helps..

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We're probably going to get yelled at soon for hijacking the thread, but it seems like an important topic.

I don't think it was PVB. I'm old enough to remember the side windows in cars using it and they never developed cataracts. PVB as used in automotive glass is also used in sheet form to do the bonding under heat and pressure. I think using it with CRTs would have required doing the reaction of the PVA with butyraldehyde in place, which sounds difficult.

But I don't know for certain. PVA seems to be mentioned in all of the old threads and Scotty used to use PVA and eventually switched to just attaching the safety glass with the tape, if I understand correctly.

http://www.videokarma.org/showthread...ight=cataracts

John

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No worries, it's not in use. It's in storage right now. I fianally found a flyback for it this year at the ETF convention. I'm going to restore it soon, and install safety glass :)

I'll study the schematic later tonight after the kids go to bed, it's nuts around here right now. I'll compare it to what's in the set to determine exactly what has been changed for the CRT.

According to the RCA Field Service Guide, the Hv should be 22.5Kv. That would be with brightness and contrast at minimum. I'll post a pic of my screen and grid connections as soon as the camera charges :mad:. Then you can compare it to yours.

Thanks-

I set it at 24kv, making the flyback a little warm after a couple hours of running. I have yet to adjust the flyback current. The schematic claims there is a fixture on the chassis for attaching your meter to while doing this adjustment-not sure where that is supposed to be.

I made up some crummy line art in paint and burned it to dvd-grids, horizontal lines, dots, etc. I did a bit of a convergence setup, but not surprisingly, it is a serious pain to do. I don't think I am getting any response out of the 3 slug coils on the board at all.

With the guidelines on establishing color balance, I adjusted for best picture while keeping G2 low. This has produced a magnificent picture,though there is still the occasional scene where I want to crawl back to the chassis and turn down the green a bit more. Where before the set only had a watchable picture with brightness and contrast all the way up, All of the controls are more or less in the middle position. If it weren't for fear of burning up the flyback (ie getting hv dialed in right) and having the convergence properly done, I'd say this thing was looking really good.

I have some early 1950s Hoffman B&W sets. The safety glass on these is true safety glass with the embedded plastic layer.

The only difference I see from original is the yellow/blue stripe and yellow/green stripe wires (pin 13 and 5 hooked together) move from the original position on the 2.7k ohm resistor (R71) to the 1.8k ohm (R70), they are now connected to the extreme end by the video output board where the peaking coil is. The yellow/red remains connected to R69 as per the schematic. see pics. I'm not an expert on this mod so if anyone else knows something, please chime in. I'm just going by what was done to my set, the picture tube was changed by the RCA service company so I assume it is correct. The tube was installed 4/15/68 and is still going strong.:thmbsp:


edit: I'm not sure my set is right, so I took down the pictures.

Ditto on a late 40s RCA that I checked. The safety glass on my '53 Philco does not have the embedded (PVB?) layer, but is nearly 1/4" thick and appears that it could be tempered... pretty strong hunk of glass.
How thick are the curved shields that have been removed from the bonded color CRTs ?

jr

They are not as thick as the ones on the un-bonded 21FBP22. It would be great to find one with a gasket from an un-bonded tube to put on the FJP when necessary. I have a tinted unfrosted one but it's scratched in the middle. I wish I could come across a few that are clear and unfrosted.

Here are some very useful tips from the RCA service update in 1960
 

There was a lot more to it than I thought, everything you need to know is right here. Thank you Steve D.:thmbsp::D I found this while digging in my files tonight. I'm glad I found it, I forgot it was there.
http://i262.photobucket.com/albums/i...DSC00555-1.jpg
http://i262.photobucket.com/albums/i...DSC00556-1.jpg
http://i262.photobucket.com/albums/i...DSC00557-1.jpg
http://i262.photobucket.com/albums/i...DSC00558-1.jpg
http://i262.photobucket.com/albums/i...DSC00559-1.jpg

Holy Crap. I'm glad you are both okay.

Has anyone tried soaking a CRT in a vat of a relatively cheap petroleum solvent like kerosene or Diesel? I'd imagine that kerosene would dissolve PVA.
I've thought about doing a test on some PVA removed from an old CRT. Cutting up the old PVA into small pieces and seeing how it reacted to different solvents. If anyone has saved some old PVA, I'd be glad to do it.