[Jeffhs]

I agree with everyone on this. If the CRT had been necked (meaning the neck was literally knocked off the back of the tube), accidentally or otherwise (!), air would have rushed in and blown the phosphors off the center of the screen, leaving a much larger spot than your set shows. Run the usual emission test on the tube; perhaps you won't have to replace it. Many times these old CRTs will have a surprising amount of life left in them; depends on how much the set was used.