What's Going on With This CRT

[Drafalske]

Hello all. New Member, first post. I'm starting my first TV restoration and have a question about the CRT. The TV is a '49 or '50 Cromwell M712A (a re-branded Tele-King 712). I bought it from the original owner's son, who had no idea when it was last used or why it was taken out of service, only that it had been "decades" and "couldn't remember if anything was wrong with it".
There seem to be no missing parts, however I do see some replaced components (a couple caps and resistors) and most of the tubes appear to be replacements. There are no obvious visible issues but apparently it was well used.
Anyhow, I'm questioning a missing area of the interior CRT coating near the high voltage lead. It looks deliberate; not the result of some failure. I've never seen this and wonder if it's OK. The CRT is a 12LP4 or 12LP4A (there is no part number on it). No other marks or tags on the CRT anywhere. Could this be a rebuilt CRT?

I do not have a CRT tester. I purchased one, just waiting on it to arrive.
I have not attempted to power up or even plug in the set yet.

Couple photos attached.

Thanks for any info.

Dave

[Yamamaya42]

Originally Posted by Drafalske

Hello all. New Member, first post. I'm starting my first TV restoration and have a question about the CRT. The TV is a '49 or '50 Cromwell M712A (a re-branded Tele-King 712). I bought it from the original owner's son, who had no idea when it was last used or why it was taken out of service, only that it had been "decades" and "couldn't remember if anything was wrong with it".
There seem to be no missing parts, however I do see some replaced components (a couple caps and resistors) and most of the tubes appear to be replacements. There are no obvious visible issues but apparently it was well used.
Anyhow, I'm questioning a missing area of the interior CRT coating near the high voltage lead. It looks deliberate; not the result of some failure. I've never seen this and wonder if it's OK. The CRT is a 12LP4 or 12LP4A (there is no part number on it). No other marks or tags on the CRT anywhere. Could this be a rebuilt CRT?

I do not have a CRT tester. I purchased one, just waiting on it to arrive.
I have not attempted to power up or even plug in the set yet.

Couple photos attached.

Thanks for any info.

Dave

I have a 12LP4 , and what you have must be rebuilt, that's the only way I can see for the DAG to be scraped off on the inside, but I have no idea why they would ever do such a thing.

12LP4 / 12LP4A are easy to tell apart... if, there is a gap you can peek in and see the backside of the phosphor, one can normally spot if its aluminized or not, mine is clearly not, and thus needs the ion trap.

What ever you got,,, it's very weird.

[jr_tech]

I’m thinking that a couple of stirrup style getters were attached to the feed through button and flashed. Have not seen that configuration before, but I have only a few sets that use 12LP4 CRTs.

jr

[Sandy G]

Haints. Boogers. Spooks.... Only things it COULD be...(Grin)

[Eric H]

I think they left it clear so the Getter could be seen, that looks okay so it's still under vacuum. I've seen Getters near the Anode button before, but there wasnt such a huge clear area.

I don't like that it only contacts half the Anode button, seems like that would be a poor connection, it may also be connecting to the getter bracket at the top end, if it works then I wouldn't worry too much about it.

The Aluminized version of the 12LP4 is a 12KP4, an A suffix means a tinted face plate I think.

[init4fun]

I found a page that lists the "A" designation as being for "Grey Filter Glass Faceplate" , so your right , the "A" does not seem to be for "Aluminized"

[MadMan]

Protip: don't trust a crt tester unless you've used it on many crt's and have a good feel for it. Mine, which read everything I plugged it to as barely alive, had bad caps and resistors. Now, having it fixed and calibrated to the best of my ability... STILL reads everything as near-dead. Even fully working crt's! So far, in my limited experience, the best method seems to be to do the minimum capacitor replacements to get the tv working just enough to get some kind of light from the crt, and use that as your determination.

Also... don't attempt rejuvenation. Not unless you've had the crt plugged into a fully functional tv chassis and it's not working.

[Notimetolooz]

Could be a messy re-build job. Dave, did you remove some of the exterior dag? Clearly someone removed some exterior dag while it was on the chassis, maybe there was a problem with arcing.

[Drafalske]

I'll try to respond to everyone.
It's good to hear that the funky getter and clear spot in the glass isn't a huge concern. It's clearly deliberate, so I'm going to assume this is a rebuilt CRT I've got here.

I'm aware not to put too much stock in a CRT tester (or any tube tester, really). Nevertheless I feel it's a good way to at least find out if it's shorted and get a general idea of the condition. My tester did arrive today (It's a Sencore CR161) and the CRT is testing as marginal, so I should at least be able to get a picture.

As for the removed portion of exterior dag, I did not do that. Cleaning off the years of funk revealed it. And I would agree that the rebuild job, if indeed that's what I'm dealing with and I think it is, was messy. Maybe this was the cheapest replacement they could get. You know how people are.

I'm going to proceed with restoring the set. I'm only the second owner in it's 70 year life. It's an oddball brand. The cabinet is nice. And it's all there, I mean, it's not even missing any knobs.
I downloaded the SAMS for it and ordered all the capacitors from Mouser today. I'll check resistors against tolerance and replace as needed while changing the caps. Probably hold off on powering it up until I've at least replaced all the eletrolytics.

Thanks for all the replies, guys. I'll keep y'all posted on the restoration. And I'm sure I'll have more questions.

D

[irext]

If the Dag hadn't been wiped off in that area you probably wouldn't have noticed it.