[Amps] 8877 on 144MHz negative grid current.

[Bill Turner]

"Negative grid current" means the grid is actually emitting current,
much like a cathode.  To the best of my knowledge there are only two
reasons why this might happen:  

1. The grid is drawing so much "normal" current that it gets hot
enough to emit.

 or 

2  The tube is gassy to the point that it acts like a "cold cathode
tube. 

Hope this helps.

73, Bill W6WRT