Dimness in the tube usually sugest a defective crt, in this case the whole tube would have to be replaced. I can't garauntee that this the case but from my experience that is what it sounds like.
I have a 36" Toshiba CRT HDTV that's about 3 years old. Over the last 2 weekd the picture has been getting darker and redder; the brightness and contrast are now up to 100%, and its still too dark. I've checked all the cables, unplugged and re-plugged. Its dark on all inputs, like the DVD player. Is the picture tube shot? Is this something I can potentially fix, or do I need a repair tech?