1962/3 Zenith 27KC20Q

[Penthode]

Well, I have pulled the chassis to give it a clean. As I had expected, the plastic on the early convergence clover leaf is shot. The later Zeniths with the bright Red, Green, Blue enclosures seem to stand the test of time but not the earlier open plastic loops. Does anyone have or know where one could get a replacement?

I see that the later Zenith Roundie sets all have the same convergence coil resistances so this would do as a last resort.
Also, the control knobs have crumbled. The plastic seems to crumble on these early Zenith color sets. I'll post some photos. Otherwise the set appears to be in good shape.

I did however find a lot of sticky gunk on the wires. It doesn't necessarily look or smell like a nicotine set. It looks more as if it is cooking grease. (I wonder if the set was in or near a kitchen?) The consistency is thick and it isn't soluble in water: it seems to dissolve with paint thinner. I'll post some photos of this. Any thoughts?

[drussell]

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.

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:

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.

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.

[kvflyer]

Originally Posted by Penthode

Well, I have pulled the chassis to give it a clean. As I had expected, the plastic on the

...

I did however find a lot of sticky gunk on the wires. It doesn't necessarily look or smell like a nicotine set. It looks more as if it is cooking grease. (I wonder if the set was in or near a kitchen?) The consistency is thick and it isn't soluble in water: it seems to dissolve with paint thinner. I'll post some photos of this. Any thoughts?

Most if not all of the plastic wires so this vintage electronics exhibit that. I know that my CTC-9 wires are like that. I believe it isn't kitchen grease; rather the plasticizer (sp) in the wire. I found that alcohol will easily remove it.

[Tubejunke]

Originally Posted by rca2000

From what I have been able to gather--that chassis is MORE rare than the earlier 29JC20 chassis today--because it was only made for a short time--before the 26KC20 replaced it totally.

I never knew that there were so many different chassis available within a fairly short time frame. Perhaps it is the Space Command option that makes the extra numbers. Mine is a 25LC30 with no remote option. Is this early, late, better or worse? Supposedly it's a 1964 5111...

[Penthode]

This weekend, I pulled the chassis from the Zenith to give it a good cleaning. My earlier assumption that it was a smoker's set was wrong. There was little trace of nicotine.

The gunk on the wires and in the bottom of the cabinet seemed to emit from the plastic wire insulation. But the plastic u-channel ring around the safety glass seemed to be the worst offender.

I washed all the plastic with alcohol to get rid of the sticky, oily gunk. The wires are still very slightly tacky but at least it is clean.

The top of the metal cabinet has some rust where I believe the previous owner kept potted plants. I was thinking of clearing off the surface to bare metal and then reapplying a wood grain. There are many practical demonstrations on You Tube and I thought I may give this a try.

http://www.youtube.com/watch?v=u_fRpJUyBDg

Here are some more photos.