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Chunksin View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chunksin Quote  Post ReplyReply Direct Link To This Post Topic: Tube swap question
    Posted: 21 Jun 2020 at 6:27pm
I have a working 20 inch monitor with some burn, it's a Kortek KTM-F 20 with a Samsung a48krd82x02 tube. If I do a yoke swap can I use pretty much any 20 inch (A48) tube with a CR23 connection? I was thinking specifically about the Chunghwa A48AGY13X57
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monstermug Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 2020 at 6:46pm
Think you have to measure the impedance of the two windings and work out if its within acceptable range.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chunksin Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 2020 at 6:51pm
Isn't the winding value on the yoke? I'm on about a complete swap, yoke and all! Just wondering if there is anything inside the tube that differs between tube models. The curvature is very similar so I'm hoping it's doable
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Monstermug Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 2020 at 6:54pm
It's the deflection board that is the factor here.  If you use the same deflection board, and an out of range yoke, it could stress the deflection board.  As for the tube itself, I think only the HV will be of concern there.  That's my understanding of how CRT works anyway. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tb2000 Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 2020 at 7:56pm
Get your multimeter, put it in the ohms range and measure the impedance of the horizontal and vertical windings. Korteks can be low impedance or high impedance (as opposed to Hantys which are low impedance). If your Kortek and the Chunghwa measure the same or "close enough" then there's no need for a yoke swap. Ideally you want to measure the inductance as well but that'll require a meter that has that function. If you can, keep to the yoke that's on the Chunghwa, setting up a yoke and rings can sometimes be simple but then sometimes can be a pain or almost impossible to get right!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chunksin Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jun 2020 at 4:40pm
Thanks both, the Chunghwa tube has a yoke for a VGA chassis at the moment hence my question specifically about swapping the yoke - the values on the existing yoke will be very different and probably won't work for CGA, I'll measure them just in case.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chunksin Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 7:27pm
Ok so my current Samsung tube yoke measures (in ohms) 13.9 and 2.0, the donor tube measures 15.4 and 4.0, would it be worth trying or is the horizontal too far out? Unfortunately I can't measure the inductance as my multimeter is quite basic

Note: I ditched the Chungwha, the new donor is a Thomson tube from an Alba 20 inch TV

Edited by Chunksin - 30 Jun 2020 at 7:53pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Liam Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jun 2020 at 10:09pm
Originally posted by Chunksin Chunksin wrote:

Ok so my current Samsung tube yoke measures (in ohms) 13.9 and 2.0, the donor tube measures 15.4 and 4.0, would it be worth trying or is the horizontal too far out? Unfortunately I can't measure the inductance as my multimeter is quite basic

Note: I ditched the Chungwha, the new donor is a Thomson tube from an Alba 20 inch TV


That's probably a good idea. You'll get a closer match from that TV, I expect. Check the impedance on it, just to be sure.



Edited by Liam - 30 Jun 2020 at 10:10pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chunksin Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 11:33am
I've been researching this, watching tube swap vids and reading up on various forums and I'm still not sure whether to go ahead and try it with the risk of blowing something on the chassis! 

As far as I understand it the yokes from the original and donor tubes need to be close to each other in terms of the length of the copper windings within the yoke itself. You can measure it in two ways, impedance measured in Ohms and inductance measured in Millihenrys and by the sounds of things the impedance measurement is merely an indicator of compatibility and to be sure you need to measure the inductance.

I also read that some yokes can be modified depending on if the windings are in series or parallel and rewired to either double or halve the values. The impedance seems to work similar to a speaker and amplifier in that if you connect a chassis to a yoke with a lower impedance you can blow the HOT but to one with higher impedance you won't damage the chassis but the image may be smaller in one or both directions. Also if your horizontal width is too small after the swap you can change a capacitor on the chassis to one of a higher or lower value to allow adjustment.

Just wanted to check that the above is correct - I'll pick up an LCR meter to properly measure the yoke, but considering the horizontal reading of 2 Ohms on the existing Samsung vs 4 Ohms on the new Thomson yoke does this sound possible?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kev A Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 11:50am
Its all quite confusing, obviously its best to use a yoke with the exact same specifications as the tube from the factory, but these Kortek chassis were used with a number of tubes, so there must be a range that's acceptable. But what that range is I have no idea, Going by your logic which sounds correct to me, worst that might happen would be an image that's too small.  I have been using a KTH-F chassis with a 21" Thompson tube, with acceptable results for a year or so without issue, measuring the old tube didnt really help much as it was the wrong type anyway, with horrible pincushion.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tb2000 Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 1:05pm
Member MKL might be the best person to ask with regards to compatibility. I think the chassis is similar to Hantarex in that it takes from 2-4 ohms horizontal and maybe 12-16 ohms vertical so it'd probably be ok. Would need to find a manual somewhere that says for sure.

Originally posted by Kev A Kev A wrote:

Its all quite confusing, obviously its best to use a yoke with the exact same specifications as the tube from the factory, but these Kortek chassis were used with a number of tubes, so there must be a range that's acceptable. But what that range is I have no idea, Going by your logic which sounds correct to me, worst that might happen would be an image that's too small.  I have been using a KTH-F chassis with a 21" Thompson tube, with acceptable results for a year or so without issue, measuring the old tube didnt really help much as it was the wrong type anyway, with horrible pincushion.
That's surprising that it works ok as being a 21" tube i'd bet it's FST and the yoke is probably around 8-10 ohms on the vertical. I'd expect a picture that's needing a lot of adjustment. I remember a while ago testing a 21" dual sync Intervideo chassis on a 19" Hanty tube and you couldn't reduce the width down quite enough to fit as the yoke it expected was a bit different!


Edited by tb2000 - 02 Jul 2020 at 1:08pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kev A Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jul 2020 at 2:30pm
Originally posted by tb2000 tb2000 wrote:

Member MKL might be the best person to ask with regards to compatibility. I think the chassis is similar to Hantarex in that it takes from 2-4 ohms horizontal and maybe 12-16 ohms vertical so it'd probably be ok. Would need to find a manual somewhere that says for sure.

Originally posted by Kev A Kev A wrote:

Its all quite confusing, obviously its best to use a yoke with the exact same specifications as the tube from the factory, but these Kortek chassis were used with a number of tubes, so there must be a range that's acceptable. But what that range is I have no idea, Going by your logic which sounds correct to me, worst that might happen would be an image that's too small.  I have been using a KTH-F chassis with a 21" Thompson tube, with acceptable results for a year or so without issue, measuring the old tube didnt really help much as it was the wrong type anyway, with horrible pincushion.
That's surprising that it works ok as being a 21" tube i'd bet it's FST and the yoke is probably around 8-10 ohms on the vertical. I'd expect a picture that's needing a lot of adjustment. I remember a while ago testing a 21" dual sync Intervideo chassis on a 19" Hanty tube and you couldn't reduce the width down quite enough to fit as the yoke it expected was a bit different!





Yeah its an FST tube, its near the end of the adjustment range, but enough to fill the screen, no strange pincushion or anything like that.



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