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Thread: Yoke doodling

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    Yoke doodling

    I thought this deserved it's own thread. It deals specifically with Yoke matching.

    So a chassis arrived but the seller thought the yoke I spoke of was was the neck connector. He's chasing that up for me as he gave it away with the tube , but hopefully he can get it back for me. Anyway... It leaves me with a massive problem as the yoke for the chassis, a b&w Motorola 23VP111A, is matched to chassis like most, and there's nowhere I can find another.

    It's the original chassis that was used in Sprint 2, so I was very happy to get it. Again, thought the yoke was coming too.. anyway, case it doesn't, I thought I put together a back up plan.

    I dug out a yoke that came from a 20" philips tube. So first up I'm wondering if that will even deflect enough, the tube is 23 "?
    I checked to see it it fits on the tube, and it does. The yoke readings were...

    H 2.5
    V 50

    The new target has these values on the schematic.

    H 2
    V 30

    I figured the Horizontal was pretty dam close, so left that and changed only the vertical.

    So here are the two set ups. Please take a look and tell me if you think it will work?

    First the wiring for the Nanao then following is the new wiring I set up for the Motorola.

    yoke doodling.jpg

    I made sure to use 1W resistors, well the equivalent anyway. For each 50 ohm resistor I took two 100ohm 1/2 ohm resistors and put them in parallel. I'm thinking maybe two 100ohm 1 watt resistors in parallel might be better still?

    I'm 90% sure that things will be OK if I power it up. I may not get the picture I'm after. The chassis was reported to have been working a week before it got pulled. I just want to get a few opinions. I'm ultimately responsible if it goes up in a cloud of smoke, but am keen to hear what people think on the topic. Cheers

    I should also mention that using a meter the yokes now measures 35 Ohms. I think that's close enough to 30.

    UPDATE: The seller has made contact with the guy and he's going to get it in the post next week.
    Last edited by taito; 13th February 2019 at 01:38 PM.

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    I'd love more information on yoke swapping myself.

    I don't have time to dive into this as i'm too busy at work, but at first glance... The deflection angle is what matters, it's not really about tube size IIRC. Princess Prin Prin put up some info here just the other day, but it's about colour tubes i think.

    The relationship between inductance and impedance is not fixed. The AC power going through the coils might be more important than the DC characteristics of the circuit, if i've even phrased that right.

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    Quote Originally Posted by buttersoft View Post
    I'd love more information on yoke swapping myself.

    I don't have time to dive into this as i'm too busy at work, but at first glance... The deflection angle is what matters, it's not really about tube size IIRC. Princess Prin Prin put up some info here just the other day, but it's about colour tubes i think.

    The relationship between inductance and impedance is not fixed. The AC power going through the coils might be more important than the DC characteristics of the circuit, if i've even phrased that right.
    Cheers buttersoft. I had a look but couldn't find Princess Prin Prin?

    But yeah... got me thinking.. there's all these magnet bars all around the original yoke that was matched to the valve tv. So I may have to get creative to make it work. At this stage I was just concerned about the little 50 ohm resistors I put in there going pop and hiking the resistance up to 50 ohms on the yoke? But even if it did, I'm theorising that it wouldn't destroy the chassis, I'd just get a skinny picture. Hopefully.

    Giving advice doesn't make anyone responsible. I'm responsible which advice I follow, others or my own. So theory's?
    Last edited by taito; 13th February 2019 at 07:37 PM.

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    the word "here" in my previous post was a link for you to click on.

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    Quote Originally Posted by buttersoft View Post
    the word "here" in my previous post was a link for you to click on.
    lol, completely missed that. Thanks buttersoft!

    Quote from.... http://forum.arcadecontrols.com/inde...tml#msg1677682

    "The CRT base type means nothing. You can have the same base on tubes starting from 14" through to 29" and bigger but that doesn't mean that a chassis made for a 14" CRT will work fine on a 28" CRT just because the neckboard fits both.

    As a general rule you can divide CRTs in two basic groups depending on the deflection angle. 90 CRTs are 14" through to 21" (there are some 21" tubes that are 110 but they're an exception) and 110 CRTs are 25" and 28" (22" became obsolete in the 80s). 29" are 110 or some other angle close to that (e.g. 114). 100 were also made but long ago and mostly in the US, not in Europe. A chassis made for 90 tubes will not work with a 110 tube (EHT requirements are different, line output circuit is different, scan coils aka yokes are different, etc.) and vice versa. And even within the same group you'll often find that the same chassis may have slight differences if made for a 14" from one made for a 21" or for a CRT made by one manufacturer and another CRT of the same size made by another manufacturer. Without detailed information on chassis circuit variants try at least not to mix 90 with 110 CRTS/chassis."
    So in a nut shell..... a yoke designed to work on a 20" with a deflection angle of 90 wont work properly with my tube of 23" which has a deflection angle of 110.

    So sadly, that's the end to this tube swapping story. Doesn't matter, I leaned a lot from the exercise and even though wont be swapping on this occasion, I'm sure there will be times in the future where I'll be swapping, now with a bit more knowledge under my belt. Thanks again @buttersoft.

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