12" round glass CRT that is in a Truetone 2D2047. The tube tests pretty good, but the cabinet is shot. I might want to harvest this tube for my Admiral 20X122.

I never have heard of Century Television Tube. Maybe a rebuilder, but it looks like a label from a manufacturer.

http://img.photobucket.com/albums/v223/polaraligned/IMG_3137.jpg (http://smg.photobucket.com/user/polaraligned/media/IMG_3137.jpg.html)

Here is the gun structure.

http://img.photobucket.com/albums/v223/polaraligned/IMG_3138.jpg (http://smg.photobucket.com/user/polaraligned/media/IMG_3138.jpg.html)

http://img.photobucket.com/albums/v223/polaraligned/IMG_3140.jpg (http://smg.photobucket.com/user/polaraligned/media/IMG_3140.jpg.html)

You can see it uses a single magnet ion trap. When the ion trap is removed, there is no raster. The brightest raster is in the position shown.

It measures 18.25" with an 8" neck.

The measurements don't match up to a 12QP4 which has a shorter neck and is overall shorter, though from what datasheets I have seen, there was slight variation between the manufacturers. I eliminated the KP4 as it does not need an ion trap, the UP4 has a metal cone, the LP4 needs a double ion trap, but would the LP4 produce a raster with this single ion trap even if it is wrong for the CRT? If so, maybe it is an LP4 with the wrong ion trap.

What number am I missing?

No information on the internet about this model TV other than it was made by Raytheon for Western Auto, and a picture of the Raytheon sets of the era confirm this as the knobs and escutcheons are the same on this Truetone.

I also have a couple of good testing 21" B/W CRTs with no readable numbers. I have never seen this problem discussed.

I have the dimensions and I have a RCA chart of same, much like in their Receiving Tube manuals. Can I go by the dimensions to decipher the tube numbers?

What type of HV connector does it have? If it's a little button type, it could be a 12RP4 ?

BTW The Admiral 20X122 uses a 10" CRT not a 12".

I'm guessing a 12LP4 rebuilt with a different gun.
the trap looks too far back so maybe it should have a double?

Not the Dumont button style HV connector.

And that is what I first thought Eric, the trap is awful far back, but it does give a bright raster in that position.

http://img.photobucket.com/albums/v223/polaraligned/IMG_3142.jpg (http://smg.photobucket.com/user/polaraligned/media/IMG_3142.jpg.html)

I might just be a 12lp4 rebuild. I know a lot of sets say they need a double ion trap magnet but for both of the 10bp4 sets I have (which also are supposed to have a dual magnet) they only use single ones and work fine.

The other suggestions have been good, but first, let's stop and plan the project.

I am going to suggest a logical method for thinking this through, parts of which you have already done.

Per Sams, the Admiral uses a 12LP4, which is a an magnetic focused CRT and you want to replace it with a similar CRT and you do not know what the CRT in the potential donor set is.

First, see if there is a tube chart in the set to be junked. These charts are not always where you expect them to be.

Second, and this took about two minutes to do on the internet, look up the donor set service data and you quickly will see that Rider 6-41 has the schematic, Sams Servicer in folder 556 has servicing information on this set and a similar model number 2D2047B has a schematic in Sams 161-10. The Truetone uses chassis number 12AX27, if Rider is correct. Is that number on your donor chassis?

Third Look at the potential donor CRT and see if it has a number. Sometimes they are high enough on the neck to be under the yoke. Do NOT clean the neck and base yet, and use a point-source flash light to see if a faint number is visible. If none if found. Gently clean the neck with a soft brush. Look again. Sometimes if you can make out a partial number, blowing your breath on the number, to make the neck fog, which can bring it out.

The last resort is to use liquid cleaner the neck, taking care not to get any in the base to glass joint. If the number was in ink, it will be gone, but if it was acid etched, a flashlight and/or a light dusting with talcum powder will bring out a number.

If the CRT is a rebuilt as indicated by a less than perfect neck weld, often times one will find a substitute gun in the CRT, with the most common error being a bent gun in an aluminized CRT and on a non-aluminized CRT the bend angle is different, which requires a different strength magnet, which may be the case on the donor CRT.

You already have said you have measured the CRT and it is close but not quite the same. Does the angle of the bulb indicate it is the same sweep deflection angle? Does it have the same base? Is it magnetically focused like the 12LP4 or electrostatically focused? You should have a schematic (there is one on ETF) for the Admiral that you going to restore, and you have mentioned the set to be junked is working, so on the donor set, gently slide the CRT socket out and take voltages and see if they are close.

James

Thanks for your thoughtful response James.

I would like to figure out what CRT this is regardless of the set it is potentially going into, as it may be useful in the future for a different set. The Sams is wrong, and Bob Anderson is right. The Admiral is a 10BP4. Funny thing is that I knew it was a 10BP4 when I got the set a few years ago, but I only just looked at the Sams the other day and said "wow, I need a 12" CRT for that set". Another Sams mistake, but I knew better.

Anyway, I would like to know what commercial CRT this matches best so I can save it for a future set, or pass it on to another fellow in need.

I pulled the CRT yesterday and it looks like a rebuild. The weld around the neck looks terrible, almost like it is a perfectly circular crack around the whole thing. But the CRT puts out a nice bright raster.

http://img.photobucket.com/albums/v223/polaraligned/IMG_3175.jpg (http://smg.photobucket.com/user/polaraligned/media/IMG_3175.jpg.html)

http://img.photobucket.com/albums/v223/polaraligned/IMG_3180.jpg (http://smg.photobucket.com/user/polaraligned/media/IMG_3180.jpg.html)

The screen is not aluminized.

The TV it was working in does not have an electromagnetic focusing coil.

There is not a chassis number, or any numbers anywhere to indicate what the CRT is.

Maybe it is just a mutt, with the dimensions of one tube and the gun of another.

Might I guess that putting an electrostatically focused CRT into a magnetically focused set is just a matter of disconnecting the focus coil and supplying the proper focus voltage on the focus anode? or does it get more complicated than that?

Thank you.
Scott

FYI Sams 100-1 covers 3 chassis variations, of which the 20X1(model 20X122) uses the 10BP4. Both the 20Y1 and 20Z1 use the 12LP4. I think the 20X1 also has the front controls laid out similar to the older 20A1, but electrically all three chassis type are nearly identical.

Might I guess that putting an electrostatically focused CRT into a magnetically focused set is just a matter of disconnecting the focus coil and supplying the proper focus voltage on the focus anode? or does it get more complicated than that?

Thank you.
Scott

Better to leave the focus coil wired in (it'd be a pain to duplicate it's electrical characteristics in some sets), but move it so the CRT no longer sticks through it.

OK, so I went and took a look at the Truetone chassis again. It has a magnetic focusing ring. So it is not electrostatically focused, but rather magnetic.

Even though the overall length is 7/8" shorter than the RCA spec for a 12LP4, it looks like this is a 12LP4 that someone put a single ion trap on instead of the double that it calls for.

http://img.photobucket.com/albums/v223/polaraligned/IMG_3183.jpg (http://smg.photobucket.com/user/polaraligned/media/IMG_3183.jpg.html)

I'm guessing a 12LP4 rebuilt with a different gun.
the trap looks too far back so maybe it should have a double?

I think, I mentioned it on a different thread, about an original Philco 12LP4. It was pulled from a scrap set and came with a single magnet ion trap. The ion trap had a Philco part number and the CRT was an EIA 260, so it is a Philco sourced CRT. I kept the ion trap on it, when I stored the tube.
I don't remember buying a rebuilt 10BP4 or a 12LP4, when I started repairing TV's in the late 50's. They were still available.