I am working on a Mad Planets arcade project and I was also needing a replacement monitor for my Q*Bert. Originally these Gottlieb games had Wells Gardner K4900 monitors in them and so I wanted to return them to their original state.
As you can see in the photo above, the k4900 tubes that I currently had, one from a Karate Champ on the left and one from a Commando on the right, had quite heavy burn. Even the part of the tube that was lighter was quite burned in compared to the out edges.
K4900 yokes are a high impedance yoke, meaning the horizontal reads about 3.3ohms but the vertical reads about 43.
Since many "newer" TVs you'll find from the later 90s through 2006 are often low impedance with a typical maximum of 16ohms, it can be challenging to find a tube that will match the K4900 chassis for a tube swap without resorting to swapping the original K4900 yoke onto the donor tube and then need to spend additional time with yoke convergence and purity color issues.
However, one particular TV, the Hitachi CT1947T, which was made in 1984, is a "drop in" tube swap match.
I have actually come across four of these TVs since I started looking (a couple had slightly different model numbers and a chrome bezel) and I have used all of them for K4900 tube swaps. The frame of these is actually made of solid wood. I have saved many other wood/woodgrain TVs already for retro console gaming and these were going to be discarded anyway, so I didn't feel bad. The last one I saw sitting outside a Salvation Army and I knew immediately from experience that it would work for another K4900 I was refurbishing.
You can see below that the yoke readings from the TV for the horizontal are pretty close to the original K4900 yoke readings: 3.3 vs 3.7, however the vertical readings appear to be quite off: 43 vs 57.8 ohms. This doesn't seem to be much of concern though and still works fine. The horizontal reading is the more important to be specific I have found. The yokes of the other three tubes were even closer on the horizontal with closer to 3.4 ohm readings. I had also tube swapped another K4900 in the past for a burned up one in a Moon Patrol with an earlier 80s TV that had similar readings.
Inside these Hitachi TVs, three of them used an A48AAJOOX tube and the other, this one, used a Hitachi 510YTB22 tube. Apparently they are interchangeable.
Once I had the TV mounted inside the arcade monitor frame, I did need to splice in the correct yoke connector so that it plugged into the K4900 chassis. I used heat shrink to cover the soldered wires for a secure fit.
When all assembled and tested on my monitor bench, the newly tube swapped K4900 has a nice and bright, burn free image.
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