k4900 tube swap?

jay

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My 19" 4900's tube has bad burn. I would like to swap it with a readily available tv tube. Is there a list of compatible tubes somewhere? What does one do to make sure a tube will work with a certain chassis?

I know how to "ohm out" a yoke, but how do I determine if it will work with the chassis? Ohm out my existing yoke and go though as many 19" tv tubes I can find for a match?

Can I use the existing yoke on the tv tube as well? Or do I have to use the yoke I currently have and just find a tube?

Thanks once again
 
What you want to do is find a TV that has a tube that shows on this list as a CR-23 tube. Then you need to swap the K4900 yoke over to the TV tube.

Here is a list of TV's currently known to have tubes for arcade use. See if you can find one with a CR-23 neck.

http://www.junknet.net/donor-tvs

Now, I recently found an RCA at a local Goodwill that isn't on that list, but has a CR-23 neck. The tube is an A48AAB13X02.

Yoke measurements:

H - 3.8-ohms
V - 12.2-ohms

SDC11947.jpg

SDC11948.jpg

SDC11949.jpg
 
Thanks Mod, but I have a question. I'm not sure I understood you correctly.

If I do find one of these tv's (Just seeing the pics, I've seen a lot of these in my line of work).

DO I SWAP MY YOKE ALSO? Or can I use the existing one on the tube that came with the tv?

Or....If I find a tube with a yoke that ohms out correctly can I just "put it in"?

Thanks for the reply. I've gotta get this tube swapped. It looks like shit!!
 
If you find a TV with the exact same yoke measurements, you COULD get by without swapping it, although I'm sure the yoke connector on the TV would be different than what is needed for the arcade chassis - so you'd have to spice that in. If you end up with a distorted pic that you can't adjust out (and your chassis has been rebuilt), then you should probably put the original yoke on.

And you should know that early K4900 versions had a special yoke they had to match with. if it was paired with a yoke from a later 4900, you wouldn't get a good picture. You can tell if you have an early one because the last three numbers screened on the bottom will be -023...
 
Warning: The Tv mentioned below DOES have the right tube, but the yoke is bonded, so you will not be able to remove it. Now I have to find a chassis that takes those yoke measurements and has a CR-23 neckboard....

Now, I recently found an RCA at a local Goodwill that isn't on that list, but has a CR-23 neck. The tube is an A48AAB13X02.

Yoke measurements:

H - 3.8-ohms
V - 12.2-ohms

SDC11947.jpg

SDC11948.jpg

SDC11949.jpg
 
Well, good news. As the bonded yoke had pins on the top of the yoke that the wires connected to (similar to the K4600 yoke), and since the measurements were sorta close, I decided to hook it up to a K4600 - and it works! I had to decrease the vertical size, but I have a pretty damn good picture.

And I don't know why the pink of Ms. Pac looks so fade in the photos. It's nice and bright in person...

(if the image looks like it's leaning a bit, that's because I can't hold the damn camera straight)

SDC11955.jpg

SDC11953.jpg

SDC11954.jpg
 
I picked up a tv with that exact tube, mod. I haven't looked closely yet, but would all tubes of that model # have a bonded yoke? What does bonded mean exactly? I assume it means it can't be removed from the tube, but how is it attached?
 
I picked up a tv with that exact tube, mod. I haven't looked closely yet, but would all tubes of that model # have a bonded yoke? What does bonded mean exactly? I assume it means it can't be removed from the tube, but how is it attached?

This tube has a sticker on top of the magnets that says "Do not attempt to remove this bonded yoke... etc" so that's how you know it is bonded.

I'm not sure if it is bonded with epoxy, electrically, or whatever. I just know you can't get it off without breaking the tube.

As for all tubes having bonded yokes, I guess it would depend on whether they wee all done at the same place. it's possible the tube manufacturer sold the same tubes to different manufacturing plants...
 
Hey mod, I'm thinking of dropping my A48AAB13X02 into one of my k4600's. I measured the impedances of the 2 yokes. K4600 - 2.8, 8.5. A48AAB13X02 - 3.8, 11.8. Is that close enough??? I haven't ever paid attention to yoke impedances before, but I do recall hearing about low impedance vs. high impedance. Even though these values seem to be fairly significantly different (in terms of a percentage difference), is the issue that they are both low impedance and therefore pretty much compatible? I.e. low impedance yokes are fairly universally compatible with each other, and high impedance yokes are fairly universally compatible with each other? Or is it more complex than that? How close do they need to be?

EDIT: btw, if it isn't already clear, this tube has a bonded yoke just like yours.
 
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not sure exactly how close they need to be, but low impedance needs to swap with low, and high with high. Some like the 4900 is considered high at about 36, but the G07 is also high at 55, so they are too far apart.

I can tell you that this tube and yoke will definitely work with a K4600. If you plan on leaving that chassis with that tube forever, you can cut the plugs from the TV chassis to the yoke, splice the red,blue,green, yellow wires to the connectors, and then just plug the red/blue into the horizontal and the green/yellow into the vertical (marked H and V between each set of pins). Then you can flip the yoke just by rotating the connector.///
 
Sounds great. I hope to get this done tomorrow night. What do you mean by "flip the yoke"? Do you mean if you want to flip the picture vertically and/or horizontally?
 
Sounds great. I hope to get this done tomorrow night. What do you mean by "flip the yoke"? Do you mean if you want to flip the picture vertically and/or horizontally?

Yep.

Now, I cheated a bit when I did the swap, as I wasn't sure whether I was going to keep this chassis with this tube, so I used the original yoke connectors for the 4600, pinched them a little, pulled back the insulators a bit, then slipped them over the little prongs sticking out on the back side of the yoke connector plate. If you look at where the regular pins are, you'll see some small prongs directly behind each one. That's where I connected the yoke wires...
 
Ah, cool. I'll look for that. It's always nice to not have to hack wires to get a job done. Thanks! I'll post here with the results.
 
Saw the EXACT tv today at a friend of a friends house. I tried to conjure a way to get it but he wasn't going for it.
 
Well I got the swap done. The picture looks awesome with a few exceptions. First, on the left edge of the picture you can see there's a yellowish line. Not sure if that's something I can adjust out with the chassis somehow or what??? Second, there's a minor dynamic convergence problem in the upper right corner - the red is out a bit. I think I can fix it with a magnet but with the bonded yoke, I'm not 100% sure I have enough room to get it in there. Third, and probably the most bothersome to me, there is a bit of a pincushion type problem. These pics seem to exaggerate it, but nevertheless it bugs me a bit. Is there anything I can do about that? It must have something to do with the yoke and/or tube because there was no pincushion problem with the last tube I was trying (and I recapped the chassis a couple of days ago).

Other than that the picture is beautiful. Any ideas though on the first, and more importantly, the third problem? Is this what you get when you don't have an exact match on the yoke impedances?
 

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probably. I also saw a slight bow, but it's not enough to keep me from using it in a JAMMA-swap cab...
 
I did a direct swap from a TV to a G07. I got a beautiful picture, but with a slight convergence issue, a pincushion bend on the bottom of horizontal axis, and one other tiny issue. I can probably most of them out, and there is a cap on the G07 that can have the value swapped out to help the pincushion thing.

I did have to cut the yoke connectors to swap them over.

Meh, I can live with the minor imperfections though. It is WAY better than the washed out, pac burned tube.

Here in the next few weeks, me and another local are gonna start experimenting with tube swaps including swapping the degauss and yoke.
 
Yeah, I was wondering about a chassis mod to help with the pincushion. I will probably post a new thread about that. It would be really cool if we could compile a list of mods for all the common monitors to deal with yokes of different impedances. I wouldn't think it would be any more involved than changing the value of a component, or a handful of components.
 
Damn, came close today on getting a tube. Hit a few garage sales and picked up 3 19" tv's for 5$ a piece.

One was close but 1 pin off. The other 2 weren't even remotely close.

SO now I have 3 19" tv's....

Did get one of those Zizzle Pinballs though for 15$. Pretty fun little machine
 
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