Just how bad can an Ion burn be?

[Notimetolooz]

I did occur to me that the ions would be hitting the wall in a bent gun tube and since the ion trap magnet isn't strong enough to effect the ions much, they would never reach the screen. Even if the trap was mis-adjusted. I remember seeing a picture. maybe in that same book, of a gun element with a notch in the side of the aperture, produced by electron bombardment from a mis-adjusted trap.

[jr_tech]

Other than a picture (or artist conception) in one or several tv repair books that many of us have seen, has anybody here actually seen an "X" shaped ion burn in real life? Under what conditions?

jr

[Tubejunke]

Originally Posted by Notimetolooz

I did occur to me that the ions would be hitting the wall in a bent gun tube and since the ion trap magnet isn't strong enough to effect the ions much, they would never reach the screen. Even if the trap was mis-adjusted. I remember seeing a picture. maybe in that same book, of a gun element with a notch in the side of the aperture, produced by electron bombardment from a mis-adjusted trap.

Hence the reason why the traps used to be called beam benders by techs or engineers. This is a good thread, but I'm still left with a question that's been in my mind for many years, but never really needed answering as I never burned a tube. The procedure I have always used (I forget now where I learned it) is to set brightness to a mid level with the magnet in approximately the correct position (over the split/gap in the gun) and rotate for max brightness. Then move slightly back and forth again for max brightness. Sometimes corner shadows require retouching of the magnet. I assume that maladjustments that produce burn must be if the magnet is adjusted for anything but max brightness. I never have taken a chance on that and always work fast when setting one.

Here's another interesting topic that I don't believe is covered here. What about the double ion trap magnets. A crt such as a 10BP4 calls for one. I have an RCA 8T 243 (that I am trying to get rid of) that I got with a 10BP4 and it had a single trap. It did produce a raster, but reading data on the set and the tube told me that it needed this double magnet, so I found one thanks to the Internet and possibly this site. Before the WWW, it would be almost impossible to find such an item. Anyway, it's still there and I never finished the set's slated restoration. I think I will snag the trap when I find a home for it. I will of course inform the new owner who will still be getting a heck of a deal. Point being, I never knew and still don't know what the double magnet does that a single doesn't and why some tubes call for one and not the other specifically. I bet there are a bunch of BP4 owners here that are running on a single trap with no problem.

[benman94]

Is it possible that the phosphor damage in an X shape is really NOT an ion burn? I can't think of another reasonable explanation, but it wouldn't be the first time one of those repair books misattributed a symptom to the incorrect cause.

[Gleb]

I have a CRT that had worked for a long time with a misaligned ion trap magnet. The result is a sickle-shaped ion burn:



Although, it isn't very noticeable on a real picture:



The bad thing is that the misdirected electron beam may bombard and overheat an element of the gun, causing release of gases from its surface and hurting the vacuum, thus even more ions are produced

[Kevin Kuehn]

Originally Posted by Gleb

Although, it isn't very noticeable on a real picture:

Nope I can't see any ion burn in that picture.

[Zenith26kc20]

This may answer why 7JP4 tubes were not rebuilt in the past (from what I have learned). If the phosphor is dead, it may be too costly to recoat on what, at the time was becoming an obsolete tube.
I guess I'm lucky with my 10 and 12 inch tubes. I see no ion burn on any, even the really high hour.
Would a double ion trap vs a single make a burn difference?

[Gleb]

Originally Posted by Zenith26kc20

I guess I'm lucky with my 10 and 12 inch tubes

Yes you are, because the only thing responsible for ions is the quality and depth of the vacuum inside a CRT. That's why some straight-gun CRTs work for decades with no ion burn, while some others catch a horrible one in a year or two.
A fellow CRT rebuilder says that their shop has a very positive experience of rebuilding tubes with neither ion trap nor aluminizing. They use some modern, "very advanced" vacuum pumps, and ovenize CRTs very hard before evacuating.

[benman94]

I would be very leary of a Russian rebuilder. Look at the "quality" of Russian small signal tubes...

[Gleb]

Originally Posted by jr_tech

Do they do any rebuilds for customers outside of the country?

I think they could do, but safe shipping would be the main problem...

Originally Posted by benman94

Look at the "quality" of Russian small signal tubes...

And what's wrong with them? I've never bumped into any problems with Russian tubes, at least with vintage ones.
Anyway, they do provide a nice warranty, as well as use modern brand-new cathodes with 10000-hour lifetime.

P.S. If you'd like to discuss the quality, let's get started with a random example: 2A3 RCA vs 2S4S Svetlana

[benman94]

Originally Posted by Gleb

I think they could do, but safe shipping would be the main problem...



And what's wrong with them? I've never bumped into any problems with Russian tubes, at least with vintage ones.
Anyway, they do provide a nice warranty, as well as use modern brand-new cathodes with 10000-hour lifetime.

P.S. If you'd like to discuss the quality, let's get started with a random example: 2A3 RCA vs 2S4S Svetlana

I've had issues with Russian tubes, and they have a very low reputation among most audiophiles and antique radio restorers. Even the terrible Chinese tubes seem to be better. I'll wait for rebuilding to get off the ground at the ETF...

[Gleb]

Originally Posted by Tubejunke

The procedure I have always used is to set brightness to a mid level with the magnet in approximately the correct position (over the split/gap in the gun) and rotate for max brightness. Then move slightly back and forth again for max brightness

That works properly only if the magnet keeps its initial power. Howewer, Al-Ni-Co magnets are often degaussed from aging. A degaussed magnet seems to behave properly while aligning, i.e. it still provides some "max brightness" position, but this does not mean that the whole electron beam reaches the screen.

Originally Posted by bandersen

You're not going to cause ion burn by a misaligned trap but you can damage the gun elements with the electron beam

I have at least one reverse example with a bent-gun picture tube, but it could happen from a degaussed magnet as well.

Originally Posted by benman94

I've had issues with Russian tubes, and they have a very low reputation among most audiophiles and antique radio restorers

They just have to be well-chosen. There are some top-grade ones (Svetlana, MELZ - just look at the pictures I attached to the previous post), some normal "workhorses", and, as always, some crappy crap hurting the whole reputation. I'm guessing that I should write some sort of choose guide here.

[Zenith26kc20]

I have always tried to keep the ion trap with the set it came with. My highest hour is a Motorola with a 12lp4 (can't remember the chassis but I think it is either made in 1949 or 1950. Original tube as far as I can see. Good and clear, no burn and many(!) run hours! My TS-4J takes a bit to get bright but looks good after about 10 minutes.
As for Russian tubes, my worst fire breather is a Audio Research D-150 (1976). I use Svetlana 6550B types in regulator and output. This critter will kill a set of GE welded plates in about 2000 hours. I've had the Svetlana going on 3000 hours (close to needing a change according to ARC) but no sparks/blown $11.00 dollar fuses in a long time. I have heard the "C" types are better but I'll wait till it no longer meets specs to change anything. I also have the Svet "B" types in my D-115. The D-115 laughs at Chinese tubes! Then eats them!

[bandersen]

Yes, it depends on the gun design. The two basic types and bent gun and slant cut. As near as I can make out, the bent gun uses a single magnet and the slant cut uses a dual trap.

I agree with what notimetolooz posted earlier. You're not going to cause ion burn by a misaligned trap but you can damage the gun elements with the electron beam.

Here's a diagram of how the double magnet type works.

[Tubejunke]

LOL, we forgot to talk about the sets that left a single spot at dead center of the crt for a few minutes after the set was turned off. I have heard that those crts can show a burn, but I'm sure it would be after many years of service. And the only sets I've ever seen that do this are 60s sets which means that it has nothing to do with ion traps as they were gone the way of the Edsel by that point in time.

Point being I guess that not just ions can destroy the phosphor of a crt. Any type of concentration of the electron beam over a long duration will burn into the tube. That's why we turn down the brightness if working with a set that has lost vertical or horizontal deflection. I made the mistake of not doing that years ago and ended up with a perfectly performing set with a beautiful line burned into the crt.