Why do old trinitron tubes go green?

It's not just Trintrons - pretty well all decent CRTs do this. At one time to get a pure red the phosphor used was less sensitive than the others, so that gun was driven the hardest. So aged first - resulting in the green tint.

Later CRTs used a more 'orange' red which was more efficient and didn't exhibit this fault. But wasn't as good as the original when new.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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That's for sure. Anyone remember Zenith's FTM1490? Just stunning red.

Yes. First generation PAL sets in the UK - dating from about '70 - were capable of superb pictures when properly set up. Then the rot set in with PIL tubes. They may have been consistent, but never as good as a decent shadowmask.

I work in TV production, and think the grade 1 monitors used for camera setup use the same NTSC phosphors as all those years ago...

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    Dave Plowman        dave@davenoise.co.uk           London SW
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It sounds like you're speaking of the shadowmask in the past tense as if modern CRTs don't use them anymore!

The 70s tubes were delta gun types and as I remember them, the convergence (both static and dynamic) was downright evil to set up correctly. The PIL tubes only need static convergence (if that!) and don't get mis aligned as easily as the old delta gun tubes did, almost every delta gun set I ever serviced needed convergence adjustment whilst this need became extremely rare with the later PIL tubes.

green does the least work.

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Hmmm...

Trinitron is a single-gun tube. I would expect it to go dim rather than having a color shift. If it goes green, maybe by losing the ability to deflect the electron beam from stripe to stripe?

1 gun in terms of G1,G2 but 3 separate cathodes that do indeed age at different rates. I spotted a Sony PVM1354 at work today that is going green and will need a new bottle shortly. Another common age symptom is is highlight clipping of a single color, often red. It resembles a 'puddle' of the bad color. Only cure is to replace the tube.

GG

Cool, thanks for the answers. Always wondered, seems obvious when you hear the explanation.

Cheers,

h

They haven't used the old fluorgermanate red phosphor in decades, early

60's or so? I've never actually seen a CRT that used it, everything in my lifetime has been the newer orangish vanadate phosphor.

The green phosphor tends to be the most efficient, if you've ever seen a green fluorescent tube you'll see what I mean, the green is about 2x as bright as the blue and many times brighter than the red.

Grade 1 monitors used to setup the pictures from broadcast cameras use a much more 'red' phosphor than TV sets. Decent computer monitors for graphics too. I dunno what it is, but they don't generally go so 'bright' as domestic ones.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Either that or the human eye is most sensitive at the green wavelength.

It is, that's the other part of the equation, but the lumen rating is substantially higher for the green than even for white.

Next you're going to tell us how green is brighter than white - which is made up of red, green & blue......................

Depends, if it's a modern trichromatic fluorescent tube then yes, it's made up of red, green and blue phosphors mixed as appropriate to obtain the desired color temperature however the red and blue phosphors are less efficient than the green so the white tube does indeed produce fewer lumens than a green one. If it's one of the older halphosphate phosphors (CW, WW, CWX, WWX, D) then it's a single color phosphor and the emission is much more broad though with an abundance of yellow at least in the case of CW and WW.

Personally I like the 80 series trichromatic tubes, 850 is a nice cool

5000K white with 80+ CRI, 835 is a more neutral 3500K which is a bit more pleasant for living spaces. CWX is a standard halphosphate with the addition of a fluorogermanate phosphor which emits a true deep red which pushes the CRI up to around 90 but the light looks a bit pink to me. There's some other nice mixes out there but many are hard to find.

Or there's something about the color modulation that, with aging components, causes the signal to drift toward green. I have an LCD (3" screen) color TV that is about 10 years old. When driven from a composite video input (from a DVD player) it looks fine. But the broadcast signals are starting to look a bit green.

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Not sure if NTSC works the same but the PAL system only recovers R-L & B-L from the transmitted carrier, green is recovered by working out its amplitude from the sum of the R & B signals subtracted from the luma signal.

Hmmm, just sort of in relation to this thread: can anyone tell me if its worth repairing my Trinitron? Model: G420S.

The red is pretty much dead now, and the blue sometimes work and sometimes doesn't. For the most part, the green is fine. Here's a video of it a few months ago (it would flash during warming up but would eventually stabilize, but the video shows it's totally crapping it... turning it OFF then ON would fix this):

It's worth trying to resolder the neck board, that may be all it needs.