If you can rent, borrow, or buy a strap wrench, wrap the strap around the ball housing just ahead of the threads and twist it back and forth as you pull backwards. A pipe wrench will do the same thing, but the strap wrench won't put big gouges in the tube. I've also used a vise grip chain wrench to get a grip on the tube.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!