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Originally Posted by Chad Hauris
A round color tube is a "19V" tube, it has a 19 inch diagonal viewable area. (some of the very late model round tubes are labeled with a 19V" designation)
This is theoretically the same viewable area as on say a 19" Zenith solid state Chromacolor set using a 19V" rectangular tube.
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Uh, but the "19V" only refers to the diagonal of the viewable phosphor area on the front of the tube. It has nothing whatsoever to do with viewable area of the tube, or, for that matter, the typical image size shown on the screen. These are all entirely different geometric measurements, and it's easy to demonstrate the lack of relationship between them. There seems to be some confusion here in this thread.
For example, in my living room I have an old 21" roundie (19"-viewable) color and a modern 27"-viewable square-cornered rectangular set. The 27" set of course produces a rectangular picture. The roundie has the typical pumpkin-shaped mask of its ken. If I measure the height of the mask on the roundie, I see that the picture it produces is almost exactly 16 inches in height. Now I make the same measurement on the 27" set. It too produces a picture almost exactly 16 inches in height! Since both are NTSC sets, the images they produce (including non-visible areas) will have the same height/width ratio. Therefore, if both TV sets were adjusted so that the raster perfectly fit that 16 inches of visible height, and were tuned to the same program material, objects shown on both sets would appear exactly the same size. It doesn't matter that the "roundie" has a much smaller diagonal than the 27" rectangular set. The face of the 27" set also has a significantly larger viewable area as well. However, the *size* of the images they show is the same. It's just that the roundie cuts off the corners (as well as parts of the sides), so it displays a less *complete* picture, but it's the same *size*.
Here's another quick experiment which demonstrates the opposite comparison. Take a look at the attached picture. Using a paint program, I've drawn two circles of the same size, labeled A and B. Keep in mind that the "diagonal" of a circle is the same as its diameter. On circle A, I've drawn a 4:3 ratio rectangle in which the width fits just a bit outside the circle. On circle B, I've drawn a 4:3 ratio rectangle that fits just inside the circle. Obviously, rectangle A is much larger than rectangle B. If you were to measure the area of the intersections of the circles and rectangles, you'd still find rectangle A to be larger, though not nearly as much larger as the height/width of the rectangles would suggest. So, it's easy to see that a "19V" roundie (when masked to a 'pumpkin' shape) will produce images that are both larger in height/width as well as square area compared with the "19V" rectangular tube, despite the fact that both have the same viewable diagonal dimension.
[NOTES: These are "theoretical" diagrams for illustrative purposes. In reality, most color roundie sets are maksed such that the usable height of the image is maximized a bit (to get a larger image size) at the expense of width-- note that with a 16 inch picture height, the 19:16 resulting image ratio doesn't match the 4:3 ideal. So "roundie" sets usually actually cut off parts of the sides as well as the corners. Also, most 19" rectangular sets are actually rounded-off rectangles and as such have a somewhat larger image size than the CRT face would indicate; i.e. the rectangle would actually extend beyond the circle a bit if I were to really draw it like rectangle B.]
Okay, I think that's enough geometry for today.
