How Come Early CRTs contained more Ions?

[andy]

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[bgadow]

Aw, gee, Andy-now I gotta try that! Pity the next broken-down 80s set that comes my way...

[zenith2134]

Well I was talking about melted guns/grids myself...I've seen burnt phosphor. When I was trying my hand at a DIY oscilloscope I burnt plenty of it. I remember a Panasonic 12" b/w SS set from around '76, and a Mexican-made 13" Zenith knob tuner from 1988. Without the yoke it doesn't take much to ruin that center spot!!!

[John Marinello]

Loss of difflection in projection sets will cause CRT damage (x3) nearly instantaneously. Some have built-in safeguards.

[Jeffhs]

I recall reading in a very old (circa 1950s) television repair manual that misadjustment of the ion trap can also cause ion burns, some of which were very severe. The manual had a picture of a CRT screen that had suffered a very large, circular ion burn, and also a photograph of another screen that had an ion burn in the shape of the letter X. The manual stated that the round, large ion burn was more common in round CRTs, while the X-shaped burn appeared mostly in rectangular tubes.

The bright white line that appears across the CRT screen when vertical deflection is lost will burn a line directly across the middle of the tube, if the brightness isn't turned down to zero--fast. However, I have often wondered about the line that shows on a color CRT when the service switch is on (in the service position), which of course kills the vertical sweep. Is that not a potential danger to the CRT phosphors? I would think it would be. The only way I can imagine this not to be a danger to the screen is if the brightness level of the setup line is very low (just bright enough to see), and there is no way to increase or decrease the brightness of that line with the TV's own brightness control.

[jr_tech]

"I recall reading in a very old (circa 1950s) television repair manual that misadjustment of the ion trap can also cause ion burns, some of which were very severe."

Not everything that is written in these old service books is true. Go back and look at posts # 8,9, and 10 of this thread.

jr

[andy]

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[old_tv_nut]

Originally Posted by jeyurkon

Same for my Sylvania. They list it as a beam bender, though in a few places call it an ion-trap.

John

I wonder if someone once called it the "ion-trap magnet" (as in "the magnet associated with the ion trap"), and that quickly got shortened to "ion trap?"

(Just as people refer shortly to a transistor radio as a "transistor.")

[Old1625]

Originally Posted by zenith2134

The "phosphorous" vs "phosphor" thing reminds of of the old George Carlin skit: "it's not a HOT water heater; it's just a water heater!!!!" I shouldn't laugh though: I'm no chemist. Phosphor compositions & associated jargon confuse me pretty quickly.

So has anyone seen a tube where the beam-bend was so far off that it melted the grids?

If the water heater is bought from a reputable dealer it is a perfectly cool water heater. If bought from someone driving a box truck selling out in a supermarket parking lot it may be a hot water heater.

Phosphor I think is the correct term.

All the stuff mentioned in replies in this thread are (pardon my pun) on the beam. The ion spray from the cathode hit some part of the neck of the tube, or some target electrode, and did no harm.

The service life of those old CRTs was at the same time unpredictable. While there was a day when R&R CRT was normal procedure for the average tech today it is usualy R&R TV set. I had my share of the former. And now realise the latter.

Those of us that have to do this to restore an antique TV have still to do this. Otherwise it is not feasable.

[jeyurkon]

Originally Posted by old_tv_nut

I wonder if someone once called it the "ion-trap magnet" (as in "the magnet associated with the ion trap"), and that quickly got shortened to "ion trap?"

(Just as people refer shortly to a transistor radio as a "transistor.")

I hadn't thought about that. When I when back to look at the service manual, when they don't call it a beam-bender they call it an "Ion trap magnet." They always included magnet. It does make more sense.

John

[Tubejunke]

I will try to simplify and summarize in a simpler way. Anyone who believes that a mis-adjusted ion trap will not damage the face of a crt is sadly mistaken. All repair manuals of the time HIGHLY stress this, and they are what I used to find in the library as a kid. Needless to say, I have always been careful with the adjustment of the ION TRAP magnet. I think if you try to think too deeply into the engineering theories of the monochrome cathode ray tube, then it just becomes too confusing.

Just follow the instructions in any good old manual and everything will come out fine. Old TV manuals show up a lot in Goodwill stores with bookshops in them.

The best advice I could give anyone here that is new to the ion trap is: if you remove one, mark an arrow pointing toward the faceplate of the crt. This is so the polarity of the magnetic field will not be reversed. Take a FINE sharpie and just trace the positioning of the magnet on the glass of the crt neck. Then take a telescopic look down the gun and take note of the clock positioning of the magnet. This way you can't go wrong.

Now it's a whole different story when you run into a situation where the magnet has been disturbed and is out of place or missing. Maybe we could make another thread out of that.

[jr_tech]

Originally Posted by Tubejunke

Just follow the instructions in any good old manual and everything will come out fine. Old TV manuals show up a lot in Goodwill stores with bookshops in them.

The best advice I could give anyone here that is new to the ion trap is: if you remove one, mark an arrow pointing toward the faceplate of the crt. This is so the polarity of the magnetic field will not be reversed. Take a FINE sharpie and just trace the positioning of the magnet on the glass of the crt neck. Then take a telescopic look down the gun and take note of the clock positioning of the magnet. This way you can't go wrong.

Now it's a whole different story when you run into a situation where the magnet has been disturbed and is out of place or missing. Maybe we could make another thread out of that.

This is good advice, the trap alignment *procedures* in these old manuals are usually quite correct. Proper alignment of the magnet is important for several reasons, and the life of the tube can be shortened if it is not done correctly. Some stated reasons for proper adjustment:

1. Less than optimum beam current (magnet not adjusted for max brightness) means that the brightness control must be turned up higher than necessary, which can lead to premature cathode failure. This is my primary concern when adjusting the magnet.

2. Spot size/beam characteristics may suffer if the magnet is not adjusted properly. Best efficiency usually produces the sharpest picture.

3. It is possible to deposit metal from the anode to the screen if the magnet is not adjusted properly.

4. Ions can strike the screen if the magnet is not adjusted properly. No, I really don't believe this can happen, because the trap magnet is simply not strong enough to bend the ion "beam" enough to travel straight down the gun.

In many old sets that I have seen, it is very difficult to obtain "perfect" adjustment, due to a variety of conditions, such as weakened position magnets, magnetized yoke support and other nearby chassis pieces, non-uniform focus magnet field, and perhaps a few other problems. The inability to adjust the magnet to obtain max brightness without neck shadow or positioning problems indicates that "something is wrong" that can perhaps be remedied. I will try to correct any of these problems first. If I *must*, I will slightly mis-adjust the ion magnet or place a small permanent near the neck of the tube to correct the problem, and not worry about it...much.

jr

[jhalphen]

Hello Gentlemen,

Some pictures of phosphor burned CRTs

Courtesy Noriyoshi Tezuka's repair blog (Japan) translated into "Funny English" by Google:

http://translate.google.de/translate...Fvrc-tezuka%2F

It is interesting to see that serious phosphor burn is visible on the CRT even when not energized.

Best Regards

jhalphen
Paris/France

[old_tv_nut]

Originally Posted by jhalphen

Hello Gentlemen,

Some pictures of phosphor burned CRTs

Courtesy Noriyoshi Tezuka's repair blog (Japan) translated into "Funny English" by Google:

http://translate.google.de/translate...Fvrc-tezuka%2F

It is interesting to see that serious phosphor burn is visible on the CRT even when not energized.

Best Regards

jhalphen
Paris/France

These are not examples of ion burns, but rather collapse of vertical sweep, destroying the phosphor by intense electron bombardment.

[andy]

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