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Found this poking around, I'm having the same issue with my panasonic TAU series 34" and came to the conclusion it's not the incoming signal gamma. Reason it looked "perfect" driving it with my camera was a lack of 75 ohm termination, forgot I pulled the resistors on the input board.
Here's the what I found.
"The amount of electrons generated by the cathodes is related to their surface area. A cathode with more surface area creates more electrons, in a larger electron cloud, which makes focusing the electron cloud into an electron beam more difficult. Normally, only a part of the cathode emits electrons unless the CRT displays images with parts that are at full image brightness; only the parts at full brightness cause all of the cathode to emit electrons. The area of the cathode that emits electrons grows from the center outwards as brightness increases, so cathode wear may be uneven. When only the center of the cathode is worn, the CRT may light brightly those parts of images that have full image brightness but not show darker parts of images at all, in such a case the CRT displays a poor gamma characteristic."
Doubt I'm going to find another pix tube for this monster or another someone to help carry it.
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