Zenith System 3 acting up

[TUD1]

I watched my Zenith System 3 set that I got from an estate sale a few months ago for about half an hour today, and unfortunately, it started acting erratically. The picture will slowly and erractically start to get dim and then it will snap back to normal, and sometimes it will cut off completely for very brief intervals, lasting less than a second. I love this TV, and would be devastated if it broke. The picture is just outstanding, and it's a remote set.