Westinghouse K840CK15 Restoration

[etype2]

Originally Posted by trinescope

I looked at the screen on my set with a jeweler's loupe and noticed quite a few of the phosphor dots, especially the red ones, have irregular "holes" in them, probably from the manufacturing process. Sometimes it seems the whole 15GP22 production run was almost more like a prototype run instead.

RCA had 15GP22’s in pre-production as early as June, 1953 which they shared with other manufactures. The date codes on my 15GP22 indicate it was manufactured the 13th week of 1954. There was some indication that Westinghouse was manufacturing their own 15GP22’s. Any truth to this? Or were they just assembling the tubes on the line? I know that Westinghouse was working on a single gun color CRT about the same time, so they had the capability.

[trinescope]

Originally Posted by etype2

RCA had 15GP22’s in pre-production as early as June, 1953 which they shared with other manufactures. The date codes on my 15GP22 indicate it was manufactured the 13th week of 1954. There was some indication that Westinghouse was manufacturing their own 15GP22’s. Any truth to this? Or were they just assembling the tubes on the line? I know that Westinghouse was working on a single gun color CRT about the same time, so they had the capability.

Not sure who made these tubes besides RCA. Mine is also 4 13 date code.

Here is the best I could do with a phone camera to get a picture of the phosphor dots; the holes I mentioned show up mostly on the blue and red here.

[old_tv_nut]

Originally Posted by trinescope

Here is the best I could do with a phone camera to get a picture of the phosphor dots; the holes I mentioned show up mostly on the blue and red here.

Wow - never would have suspected something like this.

[etype2]

Originally Posted by trinescope

Not sure who made these tubes besides RCA. Mine is also 4 13 date code.

Here is the best I could do with a phone camera to get a picture of the phosphor dots; the holes I mentioned show up mostly on the blue and red here.

I see the same thing on mine, but only when the dots are dimly lit.

[old_tv_nut]

Originally Posted by etype2

I see the same thing on mine, but only when the dots are dimly lit.

Really curious phenomenon there!

[colorfixer]

Originally Posted by trinescope

Not sure who made these tubes besides RCA. Mine is also 4 13 date code.

Here is the best I could do with a phone camera to get a picture of the phosphor dots; the holes I mentioned show up mostly on the blue and red here.

Notice that the red dots are slightly larger than the green and blue? Remember that the red phosphor at the time was less efficient than those used for green and blue. It's known that the red gun was run harder to compensate for this, perhaps they also made the dots slightly larger to help as well?

[old_tv_nut]

Originally Posted by colorfixer

Notice that the red dots are slightly larger than the green and blue? Remember that the red phosphor at the time was less efficient than those used for green and blue. It's known that the red gun was run harder to compensate for this, perhaps they also made the dots slightly larger to help as well?

In these tubes, like all the early tubes, the size of the excited area was limited by the size of the holes in shadow mask ("positive guard band"). What you suggest could not be done until black matrix, negative guard band tubes were developed, in which the mask holes are larger than the visible area of the phosphor dots; and then it was not done, as far as I know.