Well, I've tried manually degausing with a permanent magnet with no
effect.

Any ideas, or does this sound like the tube going bad? Thanks...

R.J.

You may have to try an AC electro magnet to degauss the tube. I use to use
a Weller soldering gun in a pinch. The inductive type. Pull the trigger,
circle the screen and keep backing off until you get about three to five
feet away. This should take you 15 to 30 seconds to complete. Then let go
of the trigger. Rinse and repeat.

The AC field should de magnetize or Degauss the CRT elements.

Good luck.
Paul