I never paid much attention to the negative grid voltage limit in the 12ax7 specs. JJ and others spec -50V wrt to the cathode. Since many grids are AC coupled and some big signals can hit the cap, I'm sure I've seen more the -50V on preamp grids. I'm running into this with an OD channel I'm testing and wondering just what happens when the limit is exceeded. Is the failure mode simply arcing from grid to cathode, or is there something else going on? Has anyone ever had experience with this limit causing a failure?