PROTOTYPE COLOR CRTs

[John Folsom]

I would like to expand a bit on the information provided on prototype color CRTs by way of some examples.

I have several prototype 15GP22s, but unfortunately most of them are John Doe CRTs. That is, hey have no identifying marks, as the paper labels with the RCA "C" number prototype designation has long since fallen off. But each is clearly and individual, and may mark an incremental progression in the development of the trr-color CRT. In addition to the obvious physical changes, many changes were made to the internal structure of the RCA developmental CRTs as time went on, as well as changes to the formulation of the phosphors. But most of the details of these "invisible" changes have become obscured with the passage of the years.

Figure 1.JPG shows two metal funnel CRTs side by side. Each has 6 nuts, 3 above and 3 below, holding the internal phosphor dot plate to the CRT structure. You can see the nuts on the right CRT, but the face of the left CRT is a bit obscured. That CRT has a lot of crud on the inside of the glass, probably indicating a catastrophic leak sometime in the past and /or storage in a very bad environment. Figures 2.JPG and 3.JPG show close up views of the left and right CRT nuts, respectively. Note that the left CRT nut is just a plain hex nut, while the right nut is a decorative domed hex nut. Figure 4.JPG shows side views of the two CRTs, which are otherwise identical, with 14 pin bases, like the ones used on a 7JP4. I suspect one of these CRTs is identical to the one being auctioned on eBay, though it is difficult to tell for sure from the auction photos. Both of these prototypes may have bee C73293s, or each may have had its own "C" number.

My Sparton 16" Color TV has a 6 nut metal funnel CRT, much like the ones above, with the decorative nuts. But it has the 20-pin base used on production 15GP22s. The CRT is designated C 73547, and is shown in Figure 5.JPG. The CRT is mounted in the set, and you can see the bottom 3 nuts peeking out above the escutcheon. Figure 6.JPG shows the decorative nut in detail, and Figure 7.JPG shows the 20-pin base, which has no markings. I assume this CRT postdates the 14-pin versions.

My CBS 16" prototype Color TV also has a metal funnel CRT with a 20-pin base. But now the phosphor plate is attached with only 3 decorative nuts, equally spaced. This CRT and base are unmarked. Figure 8.JPG shows the CRT face, and Figure 9.JPG shows the CRT in its mounting cradle.

Next, is a glass funnel CRT, very similar to the familiar 15GP22. This tube is also assembled with 3 bolts (note In this configuration, the bolt heads are exposed, not the nuts). Figure 10.JPG shows the face of the CRT and 11.JPG shows the plain hex head bolt.

And there is one more variant of 15GP22, the C 73599, which is identical to a 15GP22, with all the bolts (or nuts) covered by a decorative mask. The base is not marked, and it has a paper label with the "C" number.

The CBS-Hytron 15HP22 tri-color CRT, with the phosphor dots on the faceplate, was produced in 1953-54. It was a direct substitute for the 15GP22, and was much cheaper to assemble due to the great simplification of the internal structure. Figure 13.JPG shows a 15HP22 beside a 15GP22 for comparison. Figure 12.JPG shows the 15HP22 in its mounting cradle. This CRT was used in the CBS model RX90 15" color TV, which was never marketed to the public. To my knowledge, 15HP22s were not used in any other manufacturer's sets. This CRT and the chassis for the RX90 were test vehicles for development of CBS's first commercial color TV, the model 2l05, which used the commercial 19VP22 CRT from CBS-Hytron. The 19VP22 was used by several manufactures, including Westinghouse and Motorola. But now we are in the land of commercial color CRTs, so I will stop here.

If you know of any other variants of prototype color CRTs, I would like to hear of it.

[John Folsom]

More Photos....

[John Folsom]

The last of the Photos

[Sandy G]

Damn !! Wow !! And again, WOW!!! Have you ever checked 'em to see if they worked? What a neat bunch of stuff to put into a time capsule-Do Not Open til 2525 or something. That would completely mystify 'em...-Sandy G.

[andy]

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[Eric H]

You can see the white getters on both tubes in #4
Why did most of these go to air? were they just not built as well because they were prototypes, or maybe they were stored badly at sometime? I know metal/glass tubes seem to be more prone to leak but I've got 50+ year old 16AP4's that are still good.

[John Folsom]

Eric,

Likewise, I have seen a lot of 1940s vintage metal funnel B&W CRTs which are still good. But on the other hand, all the stories one hears say that the metal funnel B&W CRTs had a reputation of being prone to leaking. And I expect the metal funnel color CRT prototypes leaked for all the same reasons. Sad, as I have 2 TVs whcih I would like to restore, if only they had good CRTs.