We were parting out some old equipment for the control boards when this tube was found inside (the PS was still functional). It was mounted horizontally with a bracket to hold the anode cap tight in a 5kV shunt regulator suppression supply from about 1990 with a dead fan so I think it got a little hot over that time. (leaded glass tube 6BK4C for X-ray shielding) Yes, tubes still make transistors.
http://www.radiomuseum.org/tubes/tube_6bk4c.html
http://www.radiomuseum.org/tubes/tube_6bk4c.html