Hell. that's nothing. My '67 Bandmaster polished off some NOS 6L6's a couple of weeks back -- by the time I got the head turned around and saw the plates the
whole plate assembly was cherry red on the right hand side tube, and hot bits of plate metal had fallen down into the top of the glass envelope (they were upside down just like your pic)!!!!
I don't know how the grid and screen resistors all survived the heat, it was a little toasty back there.