RCA 21CT55 B8802897 is Alive!

[Tomcomm]

Seems I need to reiterate a few items that continue to provoke Member comment.
#1 Why do I insist on running the new FBX and the old CRT at “extreme” ultor voltages? Well RCA and GE 21FBP22 spec sheets specify max operation at 27.5KV. This level is undoubtedly driven by fussy Government X-ray mandate. The specs also notes: “Brilliance and definition decrease with decreasing ultor voltage.” Enough said?
Since brilliance and definition increase is what I’m after why shouldn’t I run at 30Kv (109%max) on a new “modern” FBX that requires only 200ma HOT current, at a winding temp of only 112degF! This new FBX is like a brick compared to the fragile original CTC2B FBX that ran 28KV at 264ma HOT.
#2 miniman has stated that I could ”find improvements in picture quality by providing a better signal to the CRT, like gutting the decoder entirely and going with something more modern”. Apparently he has missed the point of my entire effort to demonstrate the superior picture quality of the original full BW I/Q demodulation and low level matrixing of the CTC2B chassis. Was he serious or just being facetious ?
#3 My CTC2B is not in a cabinet in the living room or bedroom used as a daily watcher. It will always reside in the garage lab and most often not operating when I’m not there. If I’m “experimenting” with it, it will be fully instrumented as I described. Besides I have two spare, exactly the same FBXs in new RCA OEM boxes in a safe place in case of a highly unlikely FBX meltdown.
#4 My grey screen 21FBP22 may not be a 21FBP22 after all. Has any member ever seen a light grey screened FB, most are olive green? Bought mine from a rebuilder for $45 who said it was an FB but it doesn’t have any markings on neck or bulb. Doesn’t all CRT rebuilds have an obvious glass weld on its neck, mine doesn’t? On close screen inspection with mag-glass there are 3dot clusters of identical light grey with single darker grey or black dots between the 3dot clusters. Could my CRT be a replacement 21GUP22 or a 21GVP22? Electronic M posted a full screen color bar off his Silvertone that looked identical to one pic I took off mine, it looked great! He stated someone at ETF said it was a 21GUP22. How about it Tom, does your 21GUP22 have a light grey non-energized screen? Please reply...Tom

[John Folsom]

Does you tube have a bonded safety glass?

[Tomcomm]

John, not bonded. My CRT had a screen safety glass held in place with a foam rubber ring.

[John Folsom]

If it is not clear, then it is a grey filter glass, which may explain your phosphor color. I have a 21FBP22 which has had its safety glass removed, and the screen is a slightly greenish tint.

I don't know how to identify you CRT type by looking at the face, but someone else may.

[miniman82]

FJP=bonded
FBP=non-bonded

Either one with the safety glass removed will look identical, the tint of the screen will let you know which phosphors are in it. Green=sulphide, paper white=rare earth. That's the way I understand it. The RCA sheet I am reading says the 21FBP22 is an all sulphide tube, but I had a rebuilt one that said right on the side of the box 'rare earth' with a grey screen... So perhaps the FBP's came in both flavors, or it could be that a rare earth tube that was bonded in effect becomes an FBP once the lens is removed.

Originally Posted by tomcomm

#1 Why do I insist on running the new FBX and the old CRT at “extreme” ultor voltages? Well RCA and GE 21FBP22 spec sheets specify max operation at 27.5KV. This level is undoubtedly driven by fussy Government X-ray mandate. The specs also notes: “Brilliance and definition decrease with decreasing ultor voltage.” Enough said?
Since brilliance and definition increase is what I’m after why shouldn’t I run at 30Kv (109%max) on a new “modern” FBX that requires only 200ma HOT current, at a winding temp of only 112degF! This new FBX is like a brick compared to the fragile original CTC2B FBX that ran 28KV at 264ma HOT.

RE: x-rays

The spec sheet carries a specific warning for shielding, even when operated at it's max ultor voltage of 'only' 27.5kv. Going over that limit implies additional risk of increased production of x-rays, so you're taking your chances. The other very good reason not to push too much voltage is not to protect the chassis, but to protect the tube itself. When the HV is increased, so does risk of internal arc within the tube. If you don't much care about the chassis or tube (or your testicles), I don't suppose it matters. Also the 6BK4C shunt regulator sheet rates 'absolute max' plate voltage at 27kv, for the same reasons as the CRT.

RE: brilliance

This is what the spec sheet says:

"Brilliance and definition decrease with decreasing ultor voltage. In general, the ultor voltage should not be less than 20,000 volts."

(the part you left out is in bold, because context matters)

Since the tube is specified to be run between 20-27.5kv, I interpret this to mean that when run at voltages lower than 20kv brightness will decrease. RCA themselves only applied 19.5kv to the early picture tubes with the CTC-5 chassis, so there's some wiggle room on the low end when you are hoping to preserve some level of performance. Where your logic runs amok is assuming that it's all good to use the same wiggle room rule at the upper end, when the reality is that maximum ratings should never be exceeded for safety reasons. I am also a mechanic, I can tell you that the same logic will not fly in engines. "it's good at 10 lbs of boost, there is no problem running 15 lbs through it." I promise you this is not the case, many people have melted expensive parts with that kind of thinking. With high voltage and vintage electronics in close proximity to your body, the chances of walking away from a 'wreck' are not as good as with a car that has air bags. Hope my analogy makes sense, it's about safety more than anything else. I fear for your safety, guess that makes me the 'attack dog' as you put it in your other thread. So be it, at least I said something. I have washed my hands of this.

[AUdubon5425]

My goodness. The man has been experimenting with this set for almost fifty years. Experimenting. It hasn't burst into flames so far - do we really need all this bickering back and forth?

[Electronic M]

Originally Posted by Tomcomm

#4 My grey screen 21FBP22 may not be a 21FBP22 after all. Has any member ever seen a light grey screened FB, most are olive green? Bought mine from a rebuilder for $45 who said it was an FB but it doesn’t have any markings on neck or bulb. Doesn’t all CRT rebuilds have an obvious glass weld on its neck, mine doesn’t? On close screen inspection with mag-glass there are 3dot clusters of identical light grey with single darker grey or black dots between the 3dot clusters. Could my CRT be a replacement 21GUP22 or a 21GVP22? Electronic M posted a full screen color bar off his Silvertone that looked identical to one pic I took off mine, it looked great! He stated someone at ETF said it was a 21GUP22. How about it Tom, does your 21GUP22 have a light grey non-energized screen? Please reply...Tom

It is ironic that somebody would bring the set up only a few hours before it had a major breakdown.....
First off it's screen is not a light gray, but rather a dark gray that matches the mask. It almost looks like a modern dark face CRT with the safety glass on (it has been too long since I have removed the glass to remember the color, and I didn't snap a picture).

It is the (I believe) factory original CRT and is a type 21GUP22.

I believe that this is the color bar pic you mentioned.

I believe that it may have been Mark who said to me at the 2010 ETF meet when I got it that he thought it may be a black matrix type. Which is quite possible. I did some cateracting this summer and was able to compare a genuine black matrix rectangular delta-gun CRT to a regular type of the same size, so if I take the tube out of the Silvertone during trouble shooting (I have to readjust the mountings anyway so why not take it a step farther) I'll get a shot of the phosphor and try to determine if it is a black matrix type.
My set is a clone of an RCA CTC-15 or CTC-16 and lacks the benifit of an IQ demod scheme. I suspect that the alignment is lousy on mine. The colorimetry heretofore has been outstanding (ignoring that the screen adjustment balance tends to vary over the course of warmup and extended viewing), but the picture detail both color and mono can't hold a candle to my 71' Zenith Chromacolor hybrid (when the Zenith's focus and color circuits feel like warming up and doing their jobs that is).

[Tomcomm]

Tom, sorry my innocent inquire broke your Silvertone! I must be more careful in my future posts. Thanks again for your interest in my inquiry and your great screen shot postings. Anyway, I now believe my 21FBP22 can't possibly be a 21GUP22 since I bought it in '64 and its " nonactive screen color" is definitely "paper-white" indicating rare-earth as miniman posted. Its most likely a "rare-earth" 21FBP22A as I always suspected and stated in my posts. So is that good or bad from a Picture Quality standpoint? Are the saturated reds of the rare-earth 21FBP22s more like the 15GP22s and 21AXP22s then the more numerous olive-green screen sulfide 21FBP22s? The last time I saw a 21AXP22 was my Dad's CTC4 when I replaced it with my present 21FBP22A 48 years ago. In fact, I haven't seen another roundy of any kind besides mine ever since. All I know is my 21FBP22A reds are obviously more "RED" then my 13in Sony Pro monitor which has SMPTE-C phosphor and my 27in Sony comb-filtered monitor. Both Sonys are orangeish-red in comparison. I was told the SMPTE-C reds make the reproduction of flesh-tones more natural? I would like to see a rare-earth, paper-white screen 21FBP22 included in any serious comparisons with other 21in roundy including Tom's 21GUP22 and the original 15GP22s.

[old_tv_nut]

Originally Posted by Tomcomm

Its most likely a "rare-earth" 21FBP22A as I always suspected and stated in my posts. So is that good or bad from a Picture Quality standpoint? Are the saturated reds of the rare-earth 21FBP22s more like the 15GP22s and 21AXP22s then the more numerous olive-green screen sulfide 21FBP22s? All I know is my 21FBP22A reds are obviously more "RED" then my 13in Sony Pro monitor which has SMPTE-C phosphor and my 27in Sony comb-filtered monitor. Both Sonys are orangeish-red in comparison. I was told the SMPTE-C reds make the reproduction of flesh-tones more natural?

All rare-earth reds are less orange than the zinc cadmium/sulfide red, especially as the sulfide red shifts even more orange at high beam current. Rare earth reds can vary somewhat among them, but not as orange as the sulfide. The big difference in all tubes after the 21AXP22 is the sulfide green, which is much more yellow than P1; and to some extent the sulfide blue, which is a deeper blue (less cyan) than the 15GP22. Other differences you see in your Sony and other sets can be due to the color matrixing, which was adjusted to get reasonably natural flesh tones. Depending on how much matrix redesign was done, you could also get a sort of auto tint action that reduced the variation in flesh tones to some degree.

You may recall that in some cases when an earlier CRT was replaced with one with more efficient red, there was a change made to the cathode drive to reduce the red Y drive. But the R-Y gain was not reduced. The reason is that the new tube also had a yellower sulfide green. This was like adding some red into every green color, so the high R-Y amplitude tended to compensate by turning off red harder on greenish colors. This corrected the range of hues from red to orange to yellow to green, but also lit up reds too brightly. This compromise was subsequently built into all consumer NTSC sets to some degree, and a SMPTE-agreed amount was built into professional monitors, but with a matrix on/off switch.

Some of the impression of "redder" reds with the older tube comes from the contrast with the P1 green but also is due to the not-overly bright reds (even if they are slightly orange) and/or due to not having a matrix that was fudged to reduce flesh tone variations.

By the way, if you want an example of "how red" NTSC reds should be, note that red traffic signals are outside the NTSC gamut, but incandescent car taillights are not. Most rare-earth tubes are actually close to NTSC red - it's the greens that are way off.

[Electronic M]

I believe that my setting the Silvertone on the carpet (thus causing the bottom vents to be blocked) because I needed to remove the set it was sitting on to make room for the CTC4 was the reason it quit. I'll have to pull the back to find the scientiffic cause of the failure.

I can't compare the 21GUP side by side to the white face 21FBP until I get the CTC4 (which is using a white face 21FBP) working right, but I can give a qualitative, across-the-Midwest comparison of the 15GP (in the CT-100 at the ETF) and the 21GUP in my set.....The 15GP has deeper greens and better saturated colors overall than any other set I've seen in operation (except maybe Nicks 21-CT-55), but my 21GUP comes closer than any other CRT I own ( and have used in a properly adjusted set) to the stunning colorimetry of the 15GP.

[Tomcomm]

Wayne. I understand the original RCA CTC2 chassis was a true I-Y/Q-Y axis chroma 90 degree quadrature demodulator system to precisely recover the two chroma components in quadrature sent by the transmitter.. However the CTC2B chassis is a R-Y/Q-Y chroma non-90 degree axis quadrature demodulator system. Seems "The General" ordered RCA engineers to adopt this "buggered" quadrature demodulation system on the CTC2B to avoid paying a license fee to I believe Philco. The R-Y axis is 90 degrees from the reference burst and 33 degrees from the proper I-Y axis, any inherent R-Y demodulator component errors could be "mostly" removed by resistor changes in the chassis's low level matrix system. My Sept 11,2007 21CT55 reactivation project notebook indicates I considered the modification of the CTC2B's irrational R-Y/Q-Y matrix to the CTC2's proper I-Y/Q-Y configuration a no-brainer, accomplished with the addition of 2 resistors as shown in Oct 13,2007. This was the first of many "experimental" modifications I would make to this chassis. I had already exchanged the original 21AXP22 for the much brighter 21FBP22A rare earth in 1965 and made no suggested chassis changes to compensate for differences in CRT brightness. The picture quality of the present 21CT55 is quite acceptable but could possibly be better with a rigorous colometry alignment in the near future.....Tom

[old_tv_nut]

Originally Posted by Electronic M

...I can't compare the 21GUP side by side to the white face 21FBP until I get the CTC4 (which is using a white face 21FBP) working right...

Actually, it should be possible to determine with the sets not operating. With a strong magnifier, you should be able to see if the phosphor dots are separated by black matrix material.

[Electronic M]

That quote of mine had NOTHING to do with checking for black matrix. I was talking about operational colorimetry.

It is difficult to get a good look at the phosphor dots of the 21GUP with the safety glass on...So I was planning to pull the tube and remove the safety glass and look at it up close with it not running (my eyes are young, and considering I've seen a delta gun black matrix CRT up close before I should be able to tell if it is one by naked eye).

[old_tv_nut]

Tom C., sorry I misread that you intended not to look for the black matrix in the non-operating condition.

If a tube is black-matrix, it definitely will not have NTSC green. The chroma electrical matrix (or equivalently, the demodulator gains and angles) can provide some correction and can give very pleasing color, but cannot make the green phosphor less yellow or improve the cyan saturation to the same level as a 15GP22. Also, the corrections that fix the hue range between red and green always result in making the reds brighter and the cyans darker than a tube with NTSC phosphors, as a result of the tube gamma characteristic.

[Tomcomm]

This is a 900X600 JPG composite containing 54 100x60 JPG 21CT55 screen-shots. No particular significance implied, since each was originally shot at 1024X768 JPG. Picture Quality screen capture has always been the main object of this RCA CTC2B monitor-only project. More full size screen shots will follow.