Found: 15GP22 (I think)

[oldradio99]

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

[rcaman]

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

[N2IXK]

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.

[oldradio99]

Originally Posted by N2IXK

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?

[Phil Nelson]

Originally Posted by oldradio99

How do I slide the neck covering?

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:



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



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.



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).



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

[WISCOJIM]

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.

.

[kvflyer]

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.

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

[David Roper]

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

[oldradio99]

Originally Posted by David Roper

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.

[David Roper]

Originally Posted by oldradio99

May never know.

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

[oldradio99]

Originally Posted by David Roper

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.

[dtvmcdonald]

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?

[Dave A]

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.

[AdamAnt316]

Originally Posted by Dave A

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.

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

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