Can I convert 1 19" med res chassis to 25" med res chassis

SuperBee4406

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Can I convert 1 19" med res chassis to 25" med res chassis

I have a working 19" WG chassis pulled from a APB. I would like to know if it can be converted to work on a 25" tube, med res?
 

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Possible? Yes

Easily? No

I know a few people looked into doing it, but after looking into it I don't think anyone even attempted it.
 
I have a working 19" WG chassis pulled from a APB. I would like to know if it can be converted to work on a 25" tube, med res?

Unless you're just doing this to see if it can be done, you'd be better off to sell that chassis and buy a 25Kxxxx chassis. That said...

IIRC, the B+ on a 19K4915 is 123V and on the 25K55xx it's 130V. Screen voltage would also jump from ~19KV to ~25KV. I know that a low B+ causes the image to shrink semi-proportionally, so if you want to play I would start by subbing the VR (IC 301 - STR380 @123V) to an STR381 (130V). Check the downstream circuits for needed tweaks and also pump up the screen voltage. Not sure if that fly will handle 25KV for any extended period, so that substitution may be the deal breaker.

This may also help:
http://www.archive.org/details/ArcadeGameManual25k5515
 
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It will. The same flyback is used in the 25" standard resolution 4900, running an anode voltage of 25kv.

-Ian

But the 25k5515 (25" Medium resolution) uses a different flyback.

There a variety of different components that need to be replaced. Regulator and Flyback are just the beginning.
 
But the 25k5515 (25" Medium resolution) uses a different flyback.

There a variety of different components that need to be replaced. Regulator and Flyback are just the beginning.

True, but the 5515 is also a redesigned circuit. Perhaps it was for reliability, or perhaps fly availability necessitated a part change that drove the circuit to be redesigned.

Assuming the tube & yoke are electrically compatible (which they may not be), the tube is geometrically designed to spread the electron beam across a 25" screen. In the end, all you're trying to do is provide the proper voltages to allow the tube to project the same image a bit farther so it can spread a bit wider at the same intensity.

I know that long before I found klov, I was shopping for a replacement chassis to have someone install. Two I bought off ebay were sold as 19K49xx's, but were actually 13" (IIRC). The arcade tech told me it would work, but that overdriving the fly would cause it to fail prematurely. All of that may have been BS, but apparently such a swap isn't unheard of.

SuperBee, what's the tube number and socket type on that 25K?
 
But the 25k5515 (25" Medium resolution) uses a different flyback.

True. And I have no idea if the 19" medium resolution chassis can be used to drive a 25" tube in a usable manner. But the flyback can handle the higher voltage. And it can handle the higher frequency of the medium resolution operation. Whether it can handle both at the same time remains to be seen.

Now, if you use the yoke from the 19" tube, and slap it onto a 25" tube, and just hook it up - it WILL work. You WILL get a picture. It won't fill the screen and it won't converge, and it'll be dim and possibly out of focus. So, it won't be usable, but you'll get a picture. The driving of the tube guns doesn't change between the size of the tube, nor does the pinout of the tube. What changes is the deflection angle, (19" tubes are 90 degree, 25" tubes are 100 degree), and the desired anode voltage increases (~19.5kv verses ~25kv).

The higher anode voltage is probably fairly easy to obtain - by bumping up the B+ and changing the HV protection circuit, you could get it to operate at the higher voltage. What's going to be hard to adjust for is the different geometry of the 25" tube. You will need to use a yoke from a 25" tube - the 19" yoke won't be able to give you a converged picture on the wrong tube. And that means that you need a yoke that the existing deflection amplifiers can drive. And even then, I don't know if the picture geometry will be correct.

If you have a 25" tube with a yoke that is very close in resistance to the one on the 19" tube, it might be worth a try - no component changes, just hook it up and see if you can get the picture to fill the screen. It'll be dim, since the 25" tube really wants a higher accelerating voltage, but provided the chassis isn't trying to drive a wildly different impedance, it shouldn't blow up anything.

-Ian
 
True. I'm assuming the OP is trying to run the 19k4915 on a 25k5515 tube and yoke.

I'd love for it to work or find a spare 25k5515 chassis. The last 25k5515 I bought from a member here that was working fine except needed a new flyback turned out to be a 25k5501. Still a bit sore on that one.
 
True, but the 5515 is also a redesigned circuit. Perhaps it was for reliability, or perhaps fly availability necessitated a part change that drove the circuit to be redesigned.

Assuming the tube & yoke are electrically compatible (which they may not be), the tube is geometrically designed to spread the electron beam across a 25" screen. In the end, all you're trying to do is provide the proper voltages to allow the tube to project the same image a bit farther so it can spread a bit wider at the same intensity.

I know that long before I found klov, I was shopping for a replacement chassis to have someone install. Two I bought off ebay were sold as 19K49xx's, but were actually 13" (IIRC). The arcade tech told me it would work, but that overdriving the fly would cause it to fail prematurely. All of that may have been BS, but apparently such a swap isn't unheard of.

SuperBee, what's the tube number and socket type on that 25K?

Yup, trying to find a replacement chassis for a 25k5515. Tube and yoke are setup for a 25k5515. Don't have the original chassis to get repaired.
 
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