I have seen many ceramic tubes glow, but you have to be in a completely dark room and the amp in transmit......I have seen a pretty blue glow on 4cx800a/gu74b, 8877, 3cx800a7, 8874, and others. 73 Tom......W4TH Tom's Tubes: Amateur radio amp tubes, G3SEK triode/tetrode boards and kits, CTHRD C.W. Keys & K4POZ Antennas. www.tomstubes.com