Prototype set is here

[Mal Fuller]

As far as convergence & purity are concerned, are you sure that the CTC-2 chassis and this developmental CRT are fully compatible with each other?

[Zenith6S321]

Wow, an almost 60 year old prototype CRT in pristine condiition actually working! It will really be something if the chassis can be made operational and get a picture. Congratulations! I wonder if the prototypes used the same phosphors as the CT100's.

[miniman82]

Originally Posted by Mal Fuller

As far as convergence & purity are concerned, are you sure that the CTC-2 chassis and this developmental CRT are fully compatible with each other?

Yes, if they were not we would not have had a decent monochrome picture on the screen. The electron gun is almost identical to a 15GP22, the pins are all the same. At this point we were not able to get color because of a chassis fault, and even if the chassis was 100% the tube needed to be degaussed and we didn't have the degausser. Therefore, we could not do any of the setup operations which would be required for proper display. A project for another day.

[Eric H]

RCA may have dropped the ball by going with the leak prone 15G, this design seems more robust.
I wonder what their reasons were, perhaps we'll find out.

[John Folsom]

Eric H, I don't think so. I have four (4) metal bell prototype color CRTs, and they are ALL down to air, and I know of several others that are also down to air. So this is the only one still under vacuum. Certainly no better than the 15GP22, and probably worse, though the data sample is rather small, hard to draw meaningful statistical conclusions.

[ChrisW6ATV]

This is fascinating, to see that early CRT working. Is it a metal-cone design? Can any of you see possible places where leakage could happen (on this tube, or the other prototypes)?

[miniman82]

If you're going to draw statistical conclusions from the types of envelopes used, it would seem more accurate to include such tubes as the 12UP4, 16GP4, 19AP4, and 21AXP22 since it's basically the same thing as this one contruction wise. So far as I know, the 15GP22 was the only one to use that infamous flange seal. *EDIT: actually I think the CBS 205 and Westinghouse tubes used a similar design.*

Now I'm not saying that welding the CRT together was a particularly good idea no matter how it's done, but it seems to me that there are probably more operational tubes with the prototype's kind of construction than there are operational 15GP22's though there were also more of the B&W ones made.

[Phil Nelson]

Yabba-dabba-doo! I was hoping to see pictures.

Phil Nelson

[John Folsom]

Possible Leaks in Metal Cone portotype color CRTs

1. Evacuation seal (copper pinch off type)
2. Wire to glass seals at base (not very likely)
3. Glass to metal seal at faceplate of tube
4. Glass to metal seal between neck and rear of metal funnel
5. 8 welded bolt heads which protrude through sides of metal bell, part of the phosphor dot plate and shadow mask mounting assembly
6. Metal to metal weld between front and back of metal funnel (similar to 21AXP22)

Summary: Lots of places for these tubes to leak!

[Electronic M]

I had the honor of seeing this historic event in person. I just happened to be there today to purchase some sets, and stayed to see if the prototype CRT would light. I figured I was going to miss the power up of the CRT so I did not bring my camera, but got some shots on the cell phone. If I can figure out how to get them off of the phone I'll post them, and email them to miniman82 as promised. I wish I had the presence of mind to bring my degaussing coil.
I even got some pictures of the set with the green beter converged than on the first moments of it displaying video.

This is definitly the most historic TV related event I've ever attended, and perhaps the most historic event I'll ever attend!!!

What an amazing experience to be among the few to see perhaps the only working original prototype shadowmask color tube display picture for the first time in several decades!

I'm still amazed that I got to see that in person!

Tom C.

[MelodyMaster]

Originally Posted by John Folsom

Possible Leaks in Metal Cone portotype color CRTs

1. Evacuation seal (copper pinch off type)
2. Wire to glass seals at base (not very likely)
3. Glass to metal seal at faceplate of tube
4. Glass to metal seal between neck and rear of metal funnel
5. 8 welded bolt heads which protrude through sides of metal bell, part of the phosphor dot plate and shadow mask mounting assembly
6. Metal to metal weld between front and back of metal funnel (similar to 21AXP22)

Summary: Lots of places for these tubes to leak!

Now this has me worried. The picture on the 21AXP22 in my Admiral 29Z1 (C322C16) was pretty dim years ago. I stupidly tried flashing the cathode, but that made no difference. I'm now wondering if the tube was indeed going soft. It needs a few tubes put back in and capacitor replacements before I can try it again. If the sulfide tube IS shot at least I have a NIB 21FJP22 to replace it with.. but those rich reds will be gone.

I had a 1981 Sony XBR in which the picture tube went completely to air after 8 years. At $700 in 1990 dollars for a replacement that was the end of it.

This is a fascinaitng thread. Thank You.

[Steve McVoy]

My experience is that the 21AXP22 is much less likely to leak. We have 8 tubes, either in sets or in boxes, and none have leaked. You'd never have that luck with 15Gs.

[MelodyMaster]

Originally Posted by Steve McVoy

My experience is that the 21AXP22 is much less likely to leak. We have 8 tubes, either in sets or in boxes, and none have leaked. You'd never have that luck with 15Gs.

Good, that encourages me to get this set going again, thank you.

[Mal Fuller]

The heavy duty (D550?) Weller soldering guns double very effectively as a degaussing coil.
Try it, you'll be amazed.

[miniman82]

Originally Posted by Mal Fuller

The heavy duty (D550?) Weller soldering guns double very effectively as a degaussing coil.
Try it, you'll be amazed.

We tried my my antique Weller 145/220 watt, it didn't do anything at all. I'll get my degaussing coil back from Mark sooner or later, don't worry.