Found: 15GP22 (I think)
 

First of all I am not a TV guy. I am a radio guy. I know enough to generally just get me in trouble.

Purchased some radio related items and found this. I knew enough that I knew portal tubes were generally collectible. But that was my limit.

After I got it home and started dusting and doing some research I discovered this may be a 15GP22 that was used in a RCA CT-100.

In speaking with the seller, this tube may never have been installed in a set. Her dad was always bringing home prototypes.

I know that good tubes are better than non working.

So how can I get this tested? And how do I verify that this is a rarer color portal tube and not just some black and white portal cheapie?

Thanks

you have a winner there for sure. slide the neck componets back and see if the getters are still silver. congrats on the find.

Definitely looks like a 15GP22. The 20 pin base is a dead giveaway. This looks like it was a homebrew test jig for working on very early color sets.

There should be a marking on the neck somewhere near the base. You will want to get a look at the getters in the neck area to see if the tube has gone to air anyway.

How do I slide the neck covering? Is it screwed?

Very cool find. Why can't I ever find treasures like that? Oh well, hope it tests good for you.

There are two parts on the neck that can be slid off from the rear after you loosen them. The first is the purity coil assembly, a coffee-can like part. Through a hole in the can, you can reach in a screwdriver to loosen the clamp that holds it to the neck. Here's a photo of one of mine removed from the tube:

http://antiqueradio.org/art/temp/RCA...ilAssembly.jpg

This diagram also points out the purity coil, along with the deflection yoke:

http://antiqueradio.org/art/RCACT-10...ityDiagram.jpg

The purity coil is not very heavy. After loosening the clamp screw, turn or slide it gently in case it's kind of stuck to the neck. Once free, it just slides back off.

When that is off, you should be able to see the number 15GP22 stamped in black ink on the glass neck. If the neck is dirty, rub gently with a dry paper towel. Whether or not you find the tube marking, this looks like a 15GP22 to me.

You may be able to see the getter after removing the purity coil. In this photo, the getter is a darkish blob inside the neck glass, about halfway between the tan tube base and the area where the black coating begins.

http://antiqueradio.org/art/RCACT-100VacsealBack.jpg

If the getter material has turned all white, that's a sign that your tube has lost vacuum and can't be used in a TV. If it's dark as in that photo, or even better, if it's nice and shiny looking, then cross your fingers that the vacuum is still holding. The tube might still have other problems, but at least it's not a stone dud.

If you can't see the getter after removing the purity coil, you'll need to remove the deflection yoke. This part is much heavier than the purity coil, so you'll want to work with care while removing it. It looks like you have a sort of homebrew yoke mount. (In a CT-100, the yoke is hung by a metal frame from a stout wooden bar.) After you loosen whatever screws or nuts that mount uses, you want to slide the yoke straight back off the tube neck, just as you did the purity coil. Here's a photo of the deflection yoke removed from my CT-100 (and still attached to its wooden bar).

http://antiqueradio.org/art/temp/RCA...ntingFrame.jpg

If your getter doesn't look dark or shiny, don't lose hope as long as it's not all white. One of my 15GP22 tubes has a getter that's practically transparent, yet it tests and plays like a new one.

Taking a look at the getter will give you one piece of data, but that's not the whole story. You'll need a picture tube tester to tell whether your tube has strong enough emission to make a good color picture.

Even if the tube looks dead, it is still worth saving, since some day it may be possible to rebuild them just as in the good old days.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Great post, Phil. That should help Art immensely.

Wish I wasn't 200+ miles away, or I would have been right down there to test that tube for him. Maybe someone closer could help him with that? He's located in Bolingbrook, IL.

.

I certainly hope that this CRT is good. Not too many of them left in the world and any good ones would be priceless... well, almost anyway.

Shoot, I would be able to test it for you, but I'm out of town for a while.
I live in Naperville.

When will you be back?

Well I felt ambitious enough to remove the purity coil but that is as far as I think I will go.

From the pictures this tube almost looks brand new.

And it is confirmed to be a 15GP22.

What do you experts think?

The next question is: just what kind of set did this tube come out of?

May never know. Or if family lore is to be believed, it may never have been in a set.

I like priceless? :). :banana:

Au contraire, somebody will recognize the mounting. The yoke plug is also an item unique to the particular set.

That is why I come here. To the experts.

Really looks like a test jig, but I can't see a service shop seeing enough color sets back then to justify such a thing. Perhaps from the development labs of a set maker who was planning to license the RCA designs?

The fact that the tube is a commercial 15GP22, and not the developmental type C-73599 would lead me to believe that this thing was built after the CT-100 was on the market.

Apart from the getter, the outward appearance of a tube is not very meaningful. I have seen cruddy, scratched-up tubes that perform like brand new, and shiny-looking tubes that were dead ducks. Looking at the getter gives you one clue, but that is not very scientific, either. A better test is whether it gives strong emission on all three of its guns, something you need a CRT tester to check. Even CRT testers don't tell the whole story. I have seen tubes that don't look so hot on a tester, but which make very acceptable pictures when installed in a working TV -- which is the ultimate tester.

Phil Nelson

Perhaps a Motorola prototype or test jig? It was found in the middle of Motorolaland. (Although it lacks the copper mounts that went into Motorolas production models.)

I believe he worked for Motorola and Zenith.

That could explain it, then. Could have been part of a laboratory "breadboard" or something like that.

Probably 12/28. We are celebrating our 1st anniversary together, in Mexico.

Congratulations. We did our 40th in San Diego this year.

Holler when you get back and settled. If I find another volunteer I will post the results here.

Happy about your find. Hope it's a good tube. On the ETF website there are pics of John Folsom's prototype Zenith. It's the only TV among the others with a vertically mounted "signal" chassis, which might explain why your tube is mounted as it is. Could be from Zenith's development labs. :scratch2:
Kevin

That would be cool.

I have seen a LOT of 15GP22's in our quest to attempt a rebuild. A good set of getters would be silver to possibly charcoal gray wtih some silver in the margins. I have seen getters that look just like these before. The tubes with getters like these were leakers. IE: they had too much air in them to function.

It is likely that when you apply voltage to the filiments, they will either light dimly and/or burn out.

There is always an outside chance that I am mis-reading what I see in the photos, but I would not be optimistic. I have seen bad tubes with getters that look far better than the ones pictured in these photos. Still, you will need to test it anyhow to tell for sure.

Curious to learn what is printed on the connector. RCA perhaps? A date code hopefully. The earliest known RCA 15GP22 has a January 1954 date code.

Pete

Interesting! Motorola started with RCA CRT's, then switched to CBS Hytron, then when the 19 inchers started failing in warranty, back to RCA CRT's.

James

What pressure is necessary for a tube to test gassy?

I was just thinking that if high enough, one could test the
tube without using the heater just by applying a high
voltage to two elements, suitably current limited, or
using a 2 or 6 meter ham transmitter a few tens of watts
coupled in through a tuned circuit stepping it you to high voltage.

Do people try this?

Does anyone remember a trick using a neon transformer to test a tube for gas? I saw it once years ago and the interior lit up purple...gas.

Believe me that I am not an expert. But looking at the getter flashing inside of the neck of the tube kinda looks as though it has leaked. I don't see the bright silver and charcoal gray. But that being said, I am NOT trying to rain on the parade. I sincerely hope that this tube tests NOS.

Best of luck, and I look forward to more on this thread.

No pictures of the method used, but this page should give a good idea:

http://www.theodoregray.com/Periodic...NobleRack.html

Applying 6.3V to the heater and measuring the current will find a tube with a lot of air in it.

?? Does the filament's current draw change in an atmosphere vs. in a vacuum (prior to vaporizing)?

The filament will draw considerably more current in air than in a vacuum, because the air molecules help carry away the heat, keeping the temperature (and consequently the resistance) of the filament from rising as much as it would if insulated by a vacuum. This is the principle behind the Pirani vacuum gauge:

http://en.wikipedia.org/wiki/Pirani_gauge

The best way to do this test (without risk of burning the filament out if indeed the tube is a leaker) would be to use a constant current power supply, set for just over the rated filament current (1.8A for the 15GP22). Apply power, and allow several minutes for warmup (with current limited, the filament will be very slow to come up to temperature). Then measure the voltage drop across the filament. It should be ~ 6.3V. If considerably lower, the tube has a very appreciable gas content.

Note that this simple test will not detect lower levels of gas that could impede tube operation. But it is a simple way to identify a tube with a gross leak.

The flash may be making those getters look thinner than they actually are, hope that's the case at least.

I've seen B&W tubes with the getter so thin you could see the loop but they still checked and worked fine.

In the case of a gross leak, if full heater voltage were applied, the entire base of the CRT will get abnormally hot very quickly due to heat conduction of the air inside.

In reply to Dave A's question about testing for gas the neon transformer the answer is a resounding YES.
When I would take duds back to Olive Electronics, Don would pull out this high voltage generator that looked like a HV probe.
He'd zap the neck of the tube and ask all present if anyone wanted their piles treated.
Nice guy, but I never turned my back on him.

Not for long, however as the heaters are likely to "burn out" fairly quickly due to the higher than normal current flowing through them... been there, seen that. :(

jr

Ebay the tube. Take a chance you cant loose.