Digging into the CTC-9

[DaveWM]

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.

[andy]

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[Dave S]

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.

[zenithfan1]

Originally Posted by andy

Considering how it ages, I'm not sure why anyone would want to add new PVA. I just use some foam mounting tape in the corners as spacers (usually 2 layers thick), then seal the edge with silicone. After it's dry, I go around the edge with packing tape for a little extra strength. The safety glass will still do its job without the PVA, there will just be slightly more glare with an air gap.

+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.

[leadlike]

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?

[jeyurkon]

Originally Posted by andy

Considering how it ages, I'm not sure why anyone would want to add new PVA. I just use some foam mounting tape in the corners as spacers (usually 2 layers thick), then seal the edge with silicone. After it's dry, I go around the edge with packing tape for a little extra strength. The safety glass will still do its job without the PVA, there will just be slightly more glare with an air gap.

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.

[DaveWM]

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.

[zenithfan1]

Originally Posted by leadlike

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?

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.

[jr_tech]

Originally Posted by DaveWM

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.

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

[zenithfan1]

Originally Posted by DaveWM

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.

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.

[leadlike]

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?

[zenithfan1]

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..

[andy]

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[jeyurkon]

Originally Posted by jr_tech

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

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

[andy]

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