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Magnet core inductor out of TV set, what is is used for?

neazoi

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I have seen in CRT TVs a permanent magnet core choke used at some point. This choke usually is multi enamel wires wound together (like a litz wire). I don't recall what is the purpose of such a choke and what is it's properties?
I know that the magnet is there to "bias" the choke somehow.
 

BigBoss

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They shouldn't be Permanent Magnets.. Are you sure ??
Because Permanent Magnets disturb the deflection..
 

c_mitra

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I have seen in CRT TVs a permanent magnet core choke used at some point.
They should be fixed with glue; do not disturb them because the beam alignments will go!

They should be placed close to the gun where the beam is most susceptible. The three beams are not affected equally.

They are fixed once during manufacture and should not be disturbed. The coils, if present, should not be connected to any external circuit.
 

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I think the inductor referred to may be part of the horizontal linearity circuits. They were mounted on the main circuit board, not the CRT. If I have the right part, they were typically about 30mm long Litz wire coils with a core similar to a small (~5mm diameter) ferrite rod but it had permanent magnetism. I'm not sure of their exact characteristics but their purpose was to add a 'S' correction curve to the scan waveform to linearize the scan. Without them, the shorter distance between the electron gun and middle of the screen compared to the edges of the screen caused the picture to stretch in the middle.

Brian.
 
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"S" correction choke is a good guess, but there are many different magnetics, particularly in a color TV. It's about 20 years since I did the last CRT TV repair.
 

neazoi

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here is a photo of it. i think the magnet is glued on top of the ferrite core.

If it is an s-correction part, is there any use of it in the amateur radio world? what are the properties of the choke then, i mean can it be used as a saturable reactor permanently saturated in just one cycle of the AC applied to it? like an imperfect diode for AC.
 

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It has very little use I'm afraid. It is just an inductor with a 'kink' in its hysteresis curve as the magnet is overpowered. It is designed to work at high current (several Amps) but only at low frequency, less than 20KHz.

The core is of little use but if you can salvage the wire it can be re-used.

Brian.
 
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neazoi

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It has very little use I'm afraid. It is just an inductor with a 'kink' in its hysteresis curve as the magnet is overpowered. It is designed to work at high current (several Amps) but only at low frequency, less than 20KHz.

The core is of little use but if you can salvage the wire it can be re-used.

Brian.
It their name "S-correction chokes" ?
 

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It's a Linearity Coil and it corrects the nonlinear Horizontal Deflection Current connected in series.
 
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betwixt

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That's just advertising nonsense. They only have two connections so they can't convert anything to something else.

The term "S-correction" isn't a property of the inductor itself, it describes what it does in a CRT deflection circuit. If you think of how a CRT magnetic deflection works when moving the scan from side to side, the most obvious signal you would use would be a sawtooth waveform. The higher up the sawtooth, the stronger the magnetic field would be and the further across the screen the scan would sweep then at the end, the sudden drop in the waveform would return the scan quickly so it is ready for the next line. However, there is a problem with that, particularly if you use deflection angles greater than 90 degrees (most CRTs are > 110 degrees). If you sweep at a constant speed the picture distorts because the distance from the electron gun to the middle of the screen is shorter than the distance to the edges of the screen. To overcome the problem, a deliberate distortion is added to the scan current to compensate, this is what "S correction" does.

All it consists of is a coil around a core with a magnet on top. Given it's peculiar characteristic it can't really be used for anything else.

Brian.
 
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The photo in post #7 seems to show a simple coil with ferrite core. Are you sure that it involves a permanent magnet? Due to the open magnetic path, the core has only limited effect on the coil characteristic.
 

neazoi

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The photo in post #7 seems to show a simple coil with ferrite core. Are you sure that it involves a permanent magnet? Due to the open magnetic path, the core has only limited effect on the coil characteristic.
Yes it is definitely magnetic. I think the magnet is the top glued part. In the past I had other such coils. In one of them the magnet was not glued but held on top with thermal shrink tube. When I removed the tube, the magnet came out. But in this one it is glued.
 

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Thanks, a ferrite permanent magnet glued to the top of the drum core, probably a second one at the bottom. I agree, it can be hardly used for anything besides it's original dedication.

Expect only a small nonlinear effect, surely nothing like a diode.
 

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The article concentrates on amplification using saturated inductors but that is quite different to the way the inductor you have works. It is never used in saturation, the permanent magnet works to delay hysteresis so the MH loop becomes more rounded. Perhaps an analogy of dragging something back and forth on an elastic string might help. It doesn't prevent each limit being reached but it does make the path taken less linear. If you look at a typical magnetic hysteresis curve you will see where the 'S' comes from when the periphery of the loop becomes more rounded.

Magnetic amplifiers are not 'lost technology' but their design doesn't allow for general purpose use so more versatile methods are normally used. You can even amplify audio with a gas flame - obviously rather dangerous but it was widely used to amplify stage productions before tube amplifiers took over!

Brian.
 

neazoi

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Magnetic amplifiers are not 'lost technology' but their design doesn't allow for general purpose use so more versatile methods are normally used. You can even amplify audio with a gas flame - obviously rather dangerous but it was widely used to amplify stage productions before tube amplifiers took over!
Brian.
I think they are concentrated more on very high power and low frequency things, where power semiconductors or even power tubes can rarely do the job. Mag amps should be used in such high power situations to control things.
Anyway I am aware of the flame diode and triode things using the flame plasma. Weird things they seem in today's technology, really useful to know in a doom's day scenario :)
Some of these ideas are frequently used in space applications, very refined of course. See for example the old flywheel and how it is used today by NASA and for storing power on the grid.
 

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