Quote:
Originally Posted by rca2000
But my 29JC20 does NOT have a good tube, the red gun is weak--and will not come up. I wonder why--maybe my set got a lot more use--or the tube was defective from the beginning. It will work--but is obviously deficient on the reds.
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Hmmm, it
is interesting that the red is the one that is shot since, if I'm not mistaken, that should be an 21FBP22 picture tube in that set, isn't it, which would have had one of the newer sulphide-based red phosphors? (Although I suppose anything can go wrong with any tube!
)
Once again, I find myself referring to Peter A. Keller's excellent book, "The Cathode Ray Tube: Technology, History and Applications" (1991), pp. 180-1:
Quote:
The 21CYP22 spawned several improved versions. During the late 1950s and early 1960s the emphasis was on increasing the brightness of the color pictures. The screen efficiency of the 21CYP22 was only about 4 percent of that of a similar size monochrome picture tube due to the shadow mask losses and the low efficiency of the red and blue phosphors, which accounted for two-thirds of the screen area. The red phosphor, zinc phosphate: manganese, was particularly troublesome. Not only was its efficiency poor but the color was more orange than red. The 21FBP22 was introduced in 1961 utilizing an all-sulphide phosphor screen patented by Austin Hardy of RCA.* A 50 percent gain in brightness was achieved. Furthermore, all three electron guns operated at about the same beam current to produce white. Previously, short life of the red gun cathode was a serious problem since it had to be driven harder than the green and blue cathodes for proper color balance. It was very common to encounter early color tubes with only two out of three guns working properly with the red gun almost always being the "sick" one. Improved brazed cathode assemblies also increased stability of color balance and contributed to longer life. An otherwise similar tube, the 21FJP22 by RCA (1961), was the first color tube to use a tempered-glass implosion shield laminated to the faceplate. Separate glass implosion windows were prone to dust accumulation between the tube and window because of the high-voltage charging of the faceplate glass and frequent disassembly and cleaning were required. Multiple reflections of ambient light also was a problem from the separate glass surfaces.
One of the most important developments during the early color years was the so-called rare-earth phosphor screen in 1964. Actually only the red phosphor was a rare-earth material, usually based on yttrium with europium activator. The 21FBP22-A used a yttrium vanadate phosphor originally developed by Sylvania and although it did not produce a quantum leap in screen brightness, it did serve to focus phosphor research on the possibilities of rare-earth emitters which would soon become a permanent solution to the brightness problem.**
* Larach, S. and Hardy, A.E. "Cathode-Ray-Tube Phosphors: Principles and Applications," Proc IEEE, Vol 61, No. 7, pp. 915-926, July 1973.
** Hardy, A.E. "Major Developments in Phosphors and Screen Application Techniques for Cathode-Ray Tubes," RCA Engin, Vol. 25, No. 2, pp. 12-18, August/September 1979.
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This book is very interesting and a great resource, well worth the money for any interested enthusiast.
Copies may still be available directly from Mr. Keller at <kellerp4(at)frontier(dot)com> and according to:
http://videokarma.org/showthread.php?t=254771, he may even be (or have been) a member of VK.