Successful tube swap?

Scott C

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I replaced a WG K4900 (19") tube this weekend with a GE A48ACE26X tube and used the WG yoke and rings. It wasn't until after I did the following that I realized I goofed when looking it up (in the CRT Cross Reference & Compatibility Guide). Therefore, I am unsure if it is causing the following or I just have WG K49xx chassis with the same issue (seems too coincidental). Note: The GE tube has 10 pins (9 around and 1 in the area by itself) just like G07 and WG49xx tubes.

Using the original WG K4900 monitor, I tested four total WG49xx chassis. One (1) showed collapse (line running top to bottom in the middle of the screen) while (2) worked. It (2) had a bit of wave and clearly needed a cap kit due to having all original caps, but it still worked.

I swapped the tube as noted above and tested a 3rd (3) chassis and had the same collapse as noted above in (1). This seemed odd, so I tested the above working chassis (2) with the new tube and now it shows the same collapse as (1) and (3). The fourth chassis (4) was not tested on the original tube, but on the new tube is now showing the same collapse as the other three chassis. All of the chassis came from various sources and none were known to work (truly unknown, at least by me).

I am digging around for another WG49xx tube to test these on, but it sounds like the tube is smoking the chassis? Keep in mind, chassis (1) had collapse on the original WG K49xx tube before the tube swap was ever done.

I did confirm all chassis swaps were done correctly, including the DAK wire. Thoughts?

Scott C.
 
This collapse sounds a yoke issue, not the tube, assuming that the chassis was working before. Even with that one that was working, but "wavy" perhaps you had a brief connection that was broken afterward.

I'd start poking in that direction, rather than the tube. Or, perhaps I'm reading incorrectly.

To truly rule out the tube/chassis scenario, get a tested/working set of both, and try those chassis on the tested/working tube.
 
This collapse sounds a yoke issue, not the tube, assuming that the chassis was working before. Even with that one that was working, but "wavy" perhaps you had a brief connection that was broken afterward.

I'd start poking in that direction, rather than the tube. Or, perhaps I'm reading incorrectly.

To truly rule out the tube/chassis scenario, get a tested/working set of both, and try those chassis on the tested/working tube.
Thanks for the suggestions. One thing that bugs me is the yoke sits a little closer to the tube (further down the tube neck) than originally on the WG K4900 tube (maybe 1/2 inch). Is that enough to cause this type of collapse?

I have a G07 tube on a WG K4900 frame, so I will swap the yoke and retest the chassis (I was thinking of that earlier, but wanted to wait until I got feedback before going that route). I have done several other tube swaps and this is the first one with issues (again, assuming it is the tube or yoke).

Scott C.
 
I don't believe you can use a G07 yoke on a K4900. G07 is high impedance. AFAIK K4900 is low.

And regardless of where the yoke sits on the tube, the yoke will drive the electron beam, even if the purity is off. So, if there is collapse, that means that one or the other (horizontal or vertical) is not being driven, and that's why it's flat.
 
The G07, 4600 and 4900 all used the same tube, so you can swap yokes between them if you wish, as long as the chassis matches the yoke.

And yes, it seems like the issue may be with the yoke. Make sure that you are connecting it properly, then do an ohm reading on the yokes (horizontal = red/blue, vertical = yellow/green) to make sure you have a good reading. Then check the yoke connector to make sure a wire isn't coming loose...
 
When I get a little time, I plan to remove the yoke and set it again using actual G07 rubber shunts to get the correct spacing.

As for the tubes, I thought the 4600 tube was different from G07/4900 tubes. Hmmm... learn something new every day.

Scott C.
 
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