Another Westinghouse H840CK15

[etype2]

Originally Posted by trinescope

Well I have results and some more problems to overcome. I can get picture and sound. I have no color sync at this point. I need to repair the broken coil plug on the hue control and see if that helps. It seems to have normal signal flow in the chroma section when checking with a scope, it just won't sync up. I can get on both sides of the lock point with the color hold control, so that is likely OK.

Next is the HV supply. I was able to repair the damaged focus pot. I made a new resistance track using thin phenolic board and pencil lead. I applied the pencil lead to the roughed up surface of the phenolic strip until I got the correct resistance value. I then installed it in the potentiometer housing. It seems to hold up even when constantly adjusting the control. I had to replace two doorknob capacitors as well. Now I get 27KV and can't regulate it down to normal. Possibly one of the high value resistors is out of tolerance.

Last on the list is the vertical convergence transformer. The reproduction parts are no longer available so I will have to rewind it myself at some point. For now I have wired around it for testing. Of course the convergence is off, but at least I can see how the rest of the set is working.

The CRT may be weak or the kind of picture I'm getting is a result of the excessive HV. It's better than a completely dud tube at least.

Did you contact John Folsom? He may have a VCT. SEE THE BOTTOM OF THIS LINK: http://www.videokarma.org/showthread...=270450&page=5

[wkand]

Originally Posted by trinescope

Well I have results and some more problems to overcome. I can get picture and sound. I have no color sync at this point. I need to repair the broken coil plug on the hue control and see if that helps. It seems to have normal signal flow in the chroma section when checking with a scope, it just won't sync up. I can get on both sides of the lock point with the color hold control, so that is likely OK.

Next is the HV supply. I was able to repair the damaged focus pot. I made a new resistance track using thin phenolic board and pencil lead. I applied the pencil lead to the roughed up surface of the phenolic strip until I got the correct resistance value. I then installed it in the potentiometer housing. It seems to hold up even when constantly adjusting the control. I had to replace two doorknob capacitors as well. Now I get 27KV and can't regulate it down to normal. Possibly one of the high value resistors is out of tolerance.

.

Eric, you have made unbelievable progress in a very short time. Take a bow!!! You have used a ton of creativity in getting things to work.

Regarding the pots you repaired. How did you get the graphite from the pencil lead to adhere to the phenolic board? You had mentioned using a certain type of glue, but I couldn't find the reference when I reread your notes.

[etype2]

Very nice improvement.

[kvflyer]

Originally Posted by etype2

Very nice improvement.

And "getting there". I will admit that as a young adult, I really looked down on the round color tube. To make it even more disgusting, I had no knowledge of the 15GP22 Kinescope! Now, I can really appreciate seeing one displaying a color image. So very cool.

I remember the hype about "Rare Earth" phosphorus and thought that this was a remarkable discovery. But red became Chinese Red, not blood red if I under stand correctly. Seems that the 15GP22 and 21AXP22 were the cat's meow colorwise?

[trinescope]

Wikipedia has a pretty good writeup about CRT phosphors. The original red wasn't very efficient to begin with, then 80% or so of the electron beam current never got past the shadow mask anyway to even light the phosphors. From what I have read, the original NTSC phosphors were used in the 15GP22, 15HP22, 19VP22, and early production 21AXP22 tubes. The later reds had a bit shorter wavelength and so appeared a bit more orange. The green phosphor was changed somewhere down the line as well, but I don't know when (probably starting with the 21CYP22). The original green is actually the same as the P1 used in old oscilloscope CRTs. Later color TV tubes first used cadmium doped phosphors, then later on the rare earth (yttrium and europium I think) phosphors.

The overall impression I get having read various articles about the subject is that the 15" color sets really were the wrong product at the time. This is when 21" B&W sets were common, and you were going to pay lots of money to get what is effectively a 12" round CRT color picture. Add to that the weird and expensive construction of the 15GP22 and that's probably why these sets were sold at fire sale prices soon after being introduced. The CBS 19" CRTs seem to be even less common than the 15" ones. It took RCA with the 21AXP22 to get color TV sales off the ground, and it still took over a decade for color TV sales to reach 50% of total.

[Electronic M]

Well the 15G development started around 1950-52 and at the time 15" was the standard screen size so it is understandable why they picked it.

The 19" color tubes only had a few months before being obsoleted by the 21" tubes.

[trinescope]

In that case the 15" tubes just ended up obsolete by the time they were ready for the market. I'm curious as to why RCA thought the best thing to do was use the separate internal faceplate in the 15GP22. It's either flat or very nearly so which introduces pincushion distortion. Maybe they thought they'd get best results getting phosphor dots on that kind of faceplate?

This set has been a real interesting experience for me. I never thought I'd run across something like this becoming available, much less with a good CRT.

[old_tv_nut]

I believe the flat internal phosphor plate was used in the 15GP22 due to technology being unavailable to create a stable curved shadow mask. The flat mask could be under tension to prevent deformation with temperature. A domed mask had to be mounted on temperature-compensating mounts that moved the mask back or forward slightly depending on temperature (and resulting contraction/expansion) in order to maintain color purity.

[jr_tech]

Yes, and in addition I believe that the phosphor dots were merely silk screened on the flat plates used in the 15GP22. The photo process to deposit the phosphor on a curved surface, using the shadow mask as a “negative” for exposure had not been perfected when these tubes were manufactured.

jr

[old_tv_nut]

"merely silk screened" doesn't quite describe it.

Zworykin and Morton describe the process in "Television" 2nd Ed. 1954. The description seems to be adapted from a 1951 paper by Barnes and Faulkner, but I believe it is the same as in the 15GP22.

Summary:
Produce the original image for etching the mask by exposing a photographic plate to a fine wire grill twice, with a rotation of 60 degrees between exposures.
Careful processing and copying reproduces a negative optical mask with round dots instead of diamond-shaped.
Expose a thin super-nickel sheet coated with photengraving enamel through the negative.
Wash away the unexposed enamel and etch the exposed metal to form the apertures with sharp feather edges.
Heat this mask and attach to the support frame while hot, so it becomes under tension.
For phosphor patterning, prepare a stencil from the mask:
[One stencil will be used for all three phosphors, with a precision displacement between applications.]
Place a Kodalith plate at the screen position with respect to the mask, and expose with a point-source carbon arc lamp placed at one gun position.
Develop the Kodalith plate.
Sueegee a protective coat of lacquer and wax onto the developed plate.
Coat with photosensitive gelatin emulsion, and expose through the plate onto the emulsion with a carbon arc lamp.
Wash away the unexposed gelatin.
Transfer the wet stencil from the plate to printing mesh and dry it.
Squeegee the phosphor suspension (phosphor powder in ethyl cellulose and amyl alcohol) onto the flat CRT glass screen.
Remove the stencil and clean it.
Allow the CRT screen to dry.
Bake the plate to remove the ethyl cellulose.
Repeat for the other two phosphors, with the stencil precisely positioned.
Bond the phosphors to the plate by misting with potassium silicate solution.
Float a nitrocellulose "blanket" onto the plate and evaporate an aluminum layer onto it.
Finally, bake to remove the nitrocellulose.

The thing to note is that the shadow mask was used as a negative, but with the intermediate stage of producing a silk screen instead of direct deposit of the phosphors.

[ppppenguin]

Originally Posted by old_tv_nut

"merely silk screened" doesn't quite describe it.

Zworykin and Morton describe the process in "Television" 2nd Ed. 1954. The description seems to be adapted from a 1951 paper by Barnes and Faulkner, but I believe it is the same as in the 15GP22.......

Mullard made a film about colour CRT production in the UK. I'm sure techniques had been refined since 1954 but the basic principles are unchaged: https://www.youtube.com/watch?v=0Qd4IX3wpZk

old_tv_nut said:
"This is the kind of thing that makes me laugh at people who ask why we can't rebuild the Saturn V rocket today to go to the moon again. It's because the tools are gone and those who developed the secret sauce for their use are too. So we have to start from scratch. Now, we may build something much better, but we still are starting from scratch. "

Not just stuff as complicated as a moon rocket. Lot of knowledge about older valve and semiconductor manufacture is also lost. And much else besides. Even if it's all well documented, the formal term for "secret sauce" is tacit knowledge, or tacit skills. The stuff that isn't in the books, often passed on by direct experience. Here at VK and other vintage forums we are helping to keep those skills alive.

https://en.wikipedia.org/wiki/Tacit_knowledge

[kvflyer]

Originally Posted by ppppenguin

Lot of knowledge about older valve and semiconductor manufacture is also lost.

As an example, who is rebuilding CRTs now that Hawkeye closed???

[Yamamaya42]

Originally Posted by kvflyer

As an example, who is rebuilding CRTs now that Hawkeye closed???

Pretty much nobody, as far as anyone knows, unless you have a heavily modified DeLorean someplace.

[trinescope]

At the risk of taking my own thread off topic, I really think the people who have been working with the rebuild equipment at ETF should practice on common B&W and color tubes first before worrying too much about pre war tubes and 15GP22s. Forget the metal cone stuff for now. Perhaps they have been, but all I hear about are attempts at rebuilding 15GP22s outside of that one monochrome tube that ended up with a 12V heater and one 21AXP22. Unfortunately their effort relies on volunteers at this point which limits the manpower available to learn and do the work and get to a point where those high value tubes can be reliably rebuilt at a reasonable price. Heck, I'd volunteer myself but I don't have the time or money to do it. I'm decades away from retirement and over a thousand miles away.

[Sandy G]

Sheesh, its a wonder they ever got any 15GPs out the door w/all THAT going on...