If you could post the information about the cabinet refinishing that was done by one of the previous owners that would be great.

I'm really glad this went to someone local to it and didn't have to travel across the country again!

Thank you all for the nice comments. The CRT test showed no emission in the test apparently, but I do not have enough details to know how exact or complete the procedure was. It was with clip leads onto a few of the CRT pins (as you would expect; I doubt there are any CRT testers with a socket for the 15GP22), and I do plan to do further testing. I have a B&K 467 CRT tester but I do not have the "universal adapter"-but this is an excuse to get the parts and make one!

I am waiting to get details of the cabinet refinishing. It is indeed a lighter color than the un-refinished areas on the edges, but it looks very nice overall.

Here are a few more pictures:

http://70.36.238.5/ct100/IMG_0347small.jpg

Inside of front panel insert.


http://70.36.238.5/ct100/IMG_0348small.jpg

Front controls, with extra potentiometers to replace original concentric ones (in right-side area).


http://70.36.238.5/ct100/IMG_0353small.jpg

Zenith(!) temporary back cover.

Hey, the cover keeps the cats out! Or other nosy critters.

Is that a Westinghouse electric range on the right?

keep us posted please at least a several times on your progress for restoration. Pics always keeps it interesting. A few months ago someone else did awesome thread and showed great working pics off a jig to show their progress of producing a functional set. It was a 15" set from another maker. Detailed posts really keeps interests in these rare sets alive. Many of us wont have chance to own one, great when collector shares experience of finding such a set.

:yes:

The stove is a gas O'Keefe & Merritt model 9100-1. It came with the house when I bought it in 1989. Recently, I did a complete cleaning job on the stove and probably got it the cleanest it has been since it was new. Those old stoves, like many other items from the past, were really built well.

More pictures:

http://70.36.238.5/ct100/IMG_0352small.jpg

The high-voltage cage. The empty tube socket in the left-center is for the 1X2B focus rectifier; there may be a solid-state diode underneath and not visible. I plan to restore this whole area back to the original circuitry to the extent I can.


http://70.36.238.5/ct100/IMG_0350small.jpg

The replacement volume/power knob. It looks pretty close to the originals I have seen.


http://70.36.238.5/ct100/IMG_0346small.jpg

The control box and knobs. The knobs are not the originals, but I may have correct ones in a box of knobs I bought years ago. (I know I have at least two, because I just saw them on a wood-cabinet 10" GE that I got without knobs and used ones from the box).

Wow, the HV might arc a little less if you just cleaned off all that soot!
Getting that Silicone off everything might be a challenge.

The Fly's on these don't put out all that much do they, most of it comes from a Tripler circuit doesn't it?

nice pics, interesting, had a early projector that had a HV tripler circuit. IS THIS the first commercially used trpler for a TV??

There's a patent link some guys invented in around late 60s for HV tripler ss box? IF
let us know of HV setup. this is the case, I'm surprised tripler design wasn't used more-- given all the flyback meltdown issues.

:yes:

Philco 48-2500 projection set has a tripler, and I think a number of other early B&W sets do.

Tripler??? Am I missing something here... mine has a 3A3 HV rectifier. a 1X2B Focus rectifier and a 6AU4GT damper... I don't see a tripler circuit. :scratch2:
jr

My mistake, I thought they used that setup.

21-CT-55 has a doubler, I think. A single 3A2 for focus, and another 2 for anode supply.

I built a universal adapter for my B&K 467 CRT tester and hooked it up tonight. I have heater-to-red-cathode leakage, so I need to isolate the heater connections. All three heaters light up, and the blue, at least, does show some emission. I did not want to turn the heater voltage up to 6.3v until I get an isolation transformer on there, though.

Do any of you know if I could use an isolation-only booster for a B&W CRT for a test? I do have a couple of them here.

I tried connecting a B&W brightener in "parallel-isolation" mode after verifying its output voltage seemed OK (connecting the brightener between the tester's heater pins and the CRT), but had no success. I will get a true source of isolated 6.3v for further tests.

With a 6V, 2A power supply hooked up, the filaments lit up OK. The B&K showed low emission (but not zero) on red and green, and blue was in the low end of the Good scale. I tried the power supply on 7.5V (its next step) for a few seconds, and all three guns read higher (as you would expect), then back down to 6V. Now the blue gun is reading solidly in the Good range, almost half-scale, and staying there. I think it may be time to order some Vacseal!

Also on my list is to see if I could use my Sylvania CK3000 test jig with the CTC-2 chassis. I have already made the adapter for the CTC-4 and CTC-5, but this one is certainly different, with its electrostatic convergence at least.

Chris,

Sounds like your crt is asleep. IF it was my set, I would get the chassis up and running so I could power it under real world conditions, to see if the crt is any good. If it turns out that the tube is under vacuum and you do NOT have the dreaded purple glow, then I would use the Beltron to wake up and CLEAN the dirty cathodes to bring back the emission.

Or... if you have a hand held tesla coil, you could also see if the tube is gassy by applying the coil to the neck of the tube. No purple would indicate a tube under solid vacuum, and then I would proceed to the Beltron cleaning to wake it up.

Bob-

Thank you for the notes. I do not have a Tesla coil, but I will proceed with the chassis restoration. (The set was apparently restored and working about 20 years ago, but I have not yet pulled it out to see the extent and type of work that was done, other than the HV picture above.) My CRT tester is a B&K 467, and it does have a clean/balance function as well as full-on rejuvenate (which would be a last resort, I am sure). I used the same model of tester many times in my work at airports to get good life out of tired tubes, but they were black-and-white CRTs.

I will post further as I make more progress.

If you didn't see a purple glow during the emissions test, then it's probably not gassy. If there was no emission then it could be gassy and not glow, but since you got good emission on the blue gun without it glowing then I think you're o.k.

John

before rejuving or cleaning with beltron or any other machine i would run it , after running for a while they may all come up and then there will be no need to rejuve or clean or whatever

mike

Like Bob says, won't get true test of (purple) gas indication until all voltages present or a tesla coil is employed.

The blue glow is from the gas being ionized. If you have emission you've got electrons moving and the couple of hundred volts used when testing a CRT accelerates them well above the few eV ionization potential of the gas.

If there were no emission, then yes the only true test would be the Tesla coil.

What's the purpose of the 2,700 ohm resistor in series with the Red cathode of the 15GP22?

Hope I'm not drifting too far off topic.

If I'm not mistaken, that's because of the early type phosphor's inability to produce equal amounts of light among the 3 colors. The resistor compensates so as the chassis can put out an equal amount bias, while the TV watcher "sees" equal amounts of light.

Charles

Roundies have cathode resistors too, there are 3 on some so the guns produce equal amounts of saturation. Example: on sets which use the 21CYP22, the red is driven at full potential, where the others are reduced somewhat.

Charles is correct.
From the RCA Color Television Home Study Course, Lesson Six

That's very interesting - I never noticed it before. Apparently besides the higher drive for red, they needed to make the current/voltage characteristic of the red gun more linear. Perhaps the much greater red drive made it more strongly non-linear than the green and blue, which would mean the midtones would not track the lowlights and highlights.

Well thats essentially correct. The rgb bias settings are a low grey starting point, and the drive adjustments are for the greater beam current, or bright white adjustment. The drive adjustments are kinda like a linearity adjustment for the tube/phosphorus combo. as overall brightness is increased. I think starting with 2X beam current on the red gun for white, by adding a resistor in the cathode circuit would actually be a current limiter. So the question is would this be limiting the max current of the gun? Someone would have to measure what is going on at several current levels of each gun while maintaining white screen to see what this resistor is doing. Current limiting on a gun driven at 2X the current of the other guns for white....

The theoretical relationship of gun current to drive voltage is a power law with a particular exponent, which has the same shape even if the three guns are driven more or less hard. The need for a series resistor indicates that the curve of light output is not exactly a power law, because the resistor will change the shape of the curve and make it more linear. This could be either an effect of the gun curve itself, or a non-linear effect of the phosphor. I think it is the gun, as phosphor effects usually consist of a loss of efficiency at high currents.
There is also some difference between grid drive (used for RGB in the CT-100) and cathode drive of the luminance (used in later sets), but apparently the later sets also found it useful to put a resistor in one or two of the cathodes even though they used cathode drive.

There's some old threads or discussions on how the new improved red phosphors were more red orange than true red. From what I heard the red phosphor was rare and hard to obtain? I really wish these weren't such finicky crts. Chris got a great deal, set had older restoration, picked up set locally and avoided costly shipping expense. That brass replacement knob IS actually solid machined brass and is quality. The finish is really a mood point, this tv is far from a basket case. Nice score.

:thmbsp:

The standard NTSC red primary is a bit orangy - for example, traffic signal red is outside the gamut of NTSC.

The original red phosphors were close to NTSC standard. The all-sulphide tube (zinc cadmium-sulfide for red) was probably the most orange, and got worse at high beam currents. The vanadate rare-earth red was pretty close to standard. The europium red that eventually became the norm is a bit orangy again, but not as bad as the sulfide.
Vanadium and europium are "rare earth" elements.

RE: Beltron,

I just wanted to relate an experience I had with a 21cyp22. Upon testing it with a B&K 465 crt tester, the tube was devoid of all emission. I had very little hope of bringing the tube back to life.

I hooked up the Beltron and set the filiment voltage at 6.3 as normal. I waited for 10 minutes and only the green gun moved just a tad to about 10% of full scale. The red and blue showed no signs of life at all. I figured this tube was a gone'r.

I next moved on to the cleaning procedure. IN this mode the Beltron is used to "wake up" a sleepy tube. The procedure is to boost filiment voltage to 12 or 13 volts and let it cook for about 20 seconds. Once again no luck on any of the guns.

Well at this point there seemed to be very little hope that this tube could be saved So I proceeded to the restoration stage were the Beltron removes surface grunge from the cathode material to expose good material,( provided there is still good cathode material to expose.)

I raised the filiment voltage to 13v, and As normally happens the 2 large blue pilot lights flickered and blinked, I processed each gun as recommended for 3 cycles. As I processed each gun the emission got up to about 97% of full scale. I was very encouraged..

When I went back to test mode all 3 guns were now between 95% and 97% of full scale.

Now for the real test. I removed the Beltron and went back to the B&K 465 tester. I like this tester for a more accurate measurement because it has a nice large 4" meter and it seems to give a better quantitive measurement of the emission than the Beltron does. The scale is calibrated from 0 to 1000 where 200 is the cutoff for good and bad. If I get a reading of over 500 and 10 seconds life with this tester I know I have a very good tube.

I set the cutoff bias and proceeded to test each gun. I was ellated to find that each gun tested between 650 and 750 and had a life test of 16 seconds on the weakest gun. I have rarely ever tested a tube that went over 800 on the B&K, not even new tubes.

Absolutely incredible for a tube that was for all practical purposes totally dead on first testing.

It is my opinion that even if a tube can be awakened through boosting filiment voltage, or just opperating for an extended period, that in itself is not enough to bring the tube back to optimum performance, because you are still trying to boil off electrons from behind a dead layer of cathode material. Sort of like trying to piss through a window screen. The Beltron not only awakens the cathode, it actually has an ability to microscopically re-expose the cathode face so that it will once again emit a proper flow of electrons. A meer awakening of the cathode will not produce an equivalent result.

I have used the Belton on 50 or more tubes since I got the unit several years ago, and in some cases the crt is just plain dead due to lack of cathode material remaining. But if there is still viable cathode material available, the Beltron can exposed the material and bring back nearly full performance to a tube that was otherwise for all practical purposes, dead. And I have never damaged a tube with the Beltron. I can't say that about the B&K. I zapped the filiments on two 10BP4's with the 465 trying to rejuvenate them before I bought my Beltron. Now I only use the B&K for emission testing.

IF this 15GP22 still has a good vacuum, and the tube has weak emission, it is very likely that it can be brought back to very good performance with the Beltron. When you get the chassis up and running, see if someone in your area has a Beltron that could come over and test and possibly clean or restore your tube. You will need to build a 20 pin to 14 pin adapter to use the Beltron 14 pin socket. It can't hurt and it will possibly restore the tube to a very good performance level. At the very least it will improve it.

Good Luck and keep us posted on your progress.

Is there a source that tells you what phosphors were used in various early color tubes? Just curious.

Phil Nelson

There were a couple of papers on the subject, telling the sequence of development of each color of phosphor individually, but incomplete information on which ones were used together, and no specific information on years or tube numbers. The combos we do know are the original yellow-plus-filter for red, then the15GP22 phosphors, which correspond to the NTSC spec, then the all-sulfide tubes, and then the rare earth tubes, first with vanadate red and then europium oxysulfide red. But there are a string of reds listed between the 15GP22 and the all sulfide tube, and no hint of how long each of those were used, or if they were mainly lab developments.

By the way, I have often wondered why RCA didn't try to do something to equalize the phosphor efficiencies in the 15GP22 (by reducing the green and blue efficiency with some sort of mixture of inactive material) in order to balance the gun currents better. There is probably some practical reason not to try it, but I don't know what that would be.

Me either, seems to me if you're gonna drive the red at max, why not drive them all at max? It's not like they stood anything to gain by not running the others at max, since any bad gun ruins the whole tube.

I appreciate the notes about the Beltron process. I have also heard that the newer B&Ks (467 which I have, and 470,480,490) and the Sencore CR70 are safe and (maybe) effective; the 467 has definitely worked well on the many B&W CRTs I have done. When I get that far, I will check around for anyone who has a Beltron here in the San Francisco area.

"
By the way, I have often wondered why RCA didn't try to do something to equalize the phosphor efficiencies in the 15GP22 (by reducing the green and blue efficiency with some sort of mixture of inactive material) in order to balance the gun currents better. There is probably some practical reason not to try it, but I don't know what that would be. "


This is an easy one to answer, Think of how contaminants will act over time and possibly really degrade the tube's performance. Also as the tube ages why degrade a color performance new, and then possibly have that gun weaken, and need to be turned up, you limit yourself. I think back then fighting short tube life was a concern always.