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My Amstrad CTM644 CRT 'monitor' (really a TV grade tube with RGB inputs), makes a high pitched whine when powered on, audible to my children and cats, though no longer to my own ears. My research indicates that this is just the scanning frequency of the tube, and not a fault of the electronics.

Did consumer CRTs always do this in the 80s, and I have forgotten? Or has my monitor got worse over time?

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  • Don't remember whether there's any iron-core magnetics handling the horizontal scan in a typical raster CRT display; but if so, then this might be relevant: en.wikipedia.org/wiki/Magnetostriction Dec 15 '20 at 15:25
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    I have always been able to hear the 15625 Hz frequency of TV screen or monitor, and I can still hear (I'm 54 now) it when I encounter one. As far as hearing this is concerned, YMMV of course.
    – chthon
    Dec 15 '20 at 17:10
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    Similar to others, I’ve always been able to hear this on every CRT monitor or TV I’ve owned, even when they were new. I always thought that the day I didn’t hear it would be my “getting old” milestone... Dec 16 '20 at 13:59
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    I remember that. I don't miss it. Dec 16 '20 at 18:18
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    I distinctly remember the 10.125 kHz 'line whistle' of TV sets using the old UK 405 line system. Dec 19 '20 at 10:27
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My Amstrad CTM644 CRT 'monitor', makes a high pitched whine [...] My research indicates that this is just the scanning frequency of the tube,

The ~15 kHz line frequency is the most likely source. More exactly, it's the retrace, as that's not only one of the most powerful moves the ray does - which equates to higher currents used to initiate it - but it's also nicely regular, so is detectable by our ears. 15 kHz is at the upper end of what humans can hear - and usually only in our first 2-3 decades, as high pitch hearing is the first thing we lose.

and not a fault of the electronics.

Erm, no. It is usually a fault of the electronics, but not with its electronic operation, but the mechanical mounting/stiffness. The sound comes from coils that move (vibrate) due to the changing magnetic fields.

Did consumer CRTs always do this in the 80s, and I have forgotten? Or has my monitor got worse over time?

Both. Often coils and the like are pressed into place and/or glued down to stop them from making these noises. When not done properly, these sounds come even with new devices.

In addition, depending on the design of the coil and its mounting, it may be temperature sensitive, meaning the device has to be heated up to ensure a proper fit. That's why this sound often comes only during warm up. This was extremely common with early (1960s) TVs, but later as well.

The problem may get worse due ageing which adds shrinking and/or loosening of the mountings. Again, depending on the design and changes this may only be an issue during warm up.

Exact measures to remove this (if possible at all) depends much on the type of circuitry and its mechanical design. The best approach would be to simply drown it in glue... except that would most likely result in overheating :( So if you want to get rid of it, a lot of experimenting is ahead of you - mind the high voltage.

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    Many thanks. I don't like sticking my hands in anything over 12V, so the cats may just have to live with it. Dec 15 '20 at 14:09
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    :) Think of it as part of the retro experience :))
    – Raffzahn
    Dec 15 '20 at 14:10
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    "That's why this sound comes often only during warm up" is definitely false. It's loudest during warm up, but I've always been able to hear when any CRT is on nearby. Dec 15 '20 at 21:26
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    I've never seen a CRT that doesn't whine. If you have a silent CRT I'd love to see it...
    – Muzer
    Dec 16 '20 at 11:22
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    Getting older is the easiest (but not least expensive) way to eliminate the noise. Dec 16 '20 at 20:15
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Basically it's the 15625 Hz sawtooth-like signal that drives the horizontal deflection coil, that is heard because the generated magnetic field moves the coil. It's a problem with all TV CRT, on some is barely audible, in other is more noticeable because the coil is more able to move. You could also hear a 50/60 Hz lower tone sometimes caused by the horizontal coil and in some sets by the mains transformer.

Anyway it's not normally a problem and the set is working as designed, or maybe the masic used to dampen the coil has dried out: not a big problem.

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