[Winky Dink]

Thanks. I think I dispersed some finely powdered alumina, not even visible, which was choking and stayed suspended for a minute or two. I couldn't resist taking the cathode and filament apart. I put it in muriatic acid for a minute to get rid of the barium oxide, then pried apart the cathode to remove the alumina-coated filament. For the record, it was a 36-inch staggered-apex folded filament.