K4900 series tube swap

[jimmy_bored]

Are all the tubes for the k4900 directly swapable.  I got one bad tube and another good tube.  If i disconnect the bad  tube(& yoke) can i just swap it with my other k4900 tube and yoke?

Thanks,

Jimmy

[Ken Layton]

Tubes are swappable, but the yokes are not as there were two different yokes and chassis made during the production run. Compare part numbers on the yokes.

The late production runs have a "vert damp" control on the main chassis and a small standup circuit board bolted to the edge of the main board. That small board is the vertical positioning board and it has a pot and a transistor on it. The early production run chassis do not have these items. These later production runs have a different yoke to accomodate these new features.

[jimmy_bored]

LOL... I knew it.  One has the extra vert board on it and the other doesn't.   

I just did a cap kit and while it improved the picture and color drastic it did not brighten the image enough.  I am figuring the tube(& yoke) is the problem and was going to change it out with another one.... But from what I read swapping the just the tube and using the same yoke is complicated.

Thanks again Ken for all your great insight!

Jimmy

[Ken Layton]

If you use the early chassis with the later yoke, there'll be a vertical foldover problem that you can't adjust out.

It's possible though that if you use the later chassis with an early yoke it MIGHT adjust out.

[jimmy_bored]

I'm just going to a complete swap(tube(yoke) & chassis).  After checking the serial number of the yokes they are different and really don't want to go through the hassle of having issues with the vert.  Its my understanding that that the incompatibility comes from the impedance rating right? Also is this the case on all series or is this just the k4900?  I am going to throw out the old tube and yoke should I document the yoke serial since I am keeping the chassis and I may come across a good tube in the future?

Thanks again..

[Ken Layton]

There were some changes done to the yoke on the later 4900's. I don't think it was so much of an impedance problem, but rather the shape of the yoke itself and the placement of the coil windings to take advantage of the new features.

Never throw the old yoke away! Someone else might need one so ebay it, but make note of the yoke part number.

The only time a yoke should ever be thrown away is if it's shorted/arcing/defective.

[jimmy_bored]

Ken,

Thanks for the great info.  I think my yoke seems to be work fine.  I see see a nice red glow, but the monitor is dull.   I can't brighten it up anymore and the colors are not vibrant.  I did a cap kit which improved it quite a bit and its now playable, but its still not good enough for me.  The monitor also takes about a 45 seconds to a minute to come up. 

I have never removed a yoke from a tube, but from what I read I think you can put any yoke on any tube?  But then I think you end up messing with the convergence rings which seems to be some major work.  Is this correct?  I bring this up because of your comment of not throwing the yoke out.  Which is exactly what i was going to do.  Given your comment on the yoke being good, do you think the problem is just with the tube?

Thanks again for all your help.  Its greatly appreciated. 

Jimmy

[SirPeale]

Sounds like your tube needs rejuvinating.

[Kevin Mullins]

A television repair shop "may" have a rejuvenator and it might clean up the tube a bit.
Usually you need to find an old school tv tech, the newer places won't have a clue about it. Worth a shot to save a tube.

[jimmy_bored]

Rejuvenating was one option I was considering.  There are no TV repair shops where I live and as a matter of fact I can't even get parts locally for my new TV's!  I always end up ordering bulbs and so forth off the internet.  So my only option would be to buy one.  In that case it sounds like everyone recommends the B & K 467 with the CR-24 or is it CR-22?  I remember seeing a post about the adapter that is needed.  For the last week I have been watching ebay and it seems that most Kits are missing some of the adapters and the person selling them knows nothing about them.  So they can't even answer that question.  I have seen other brands though like Dyno-Jet, but I don't know if that will work.  If I do get one of these tube testers is the process pretty straight forward?

Thanks!

Jimmy

[Ken Layton]

Yes the B&K model 467 is an excellent rejuvenator. Most arcade monitor tubes use adapter # CR-23 (which is still available at MCM Electronics and other B&K dealers).

[jimmy_bored]

Ken,

What about the B & K 470 and the 468?  Are those good?

Thanks,

Jimmy

[Ken Layton]

Any B&K from model 467 and up is good.