Tube glow colors Mar 7, 2014 10:40:08 GMT -6 TommyD likes this Quote Select PostDeselect PostLink to PostMemberGive GiftBack to Top Post by GnLguy on Mar 7, 2014 10:40:08 GMT -6 Good short article on how to interpret the various colors glowing within a vacuum tube.www.thetubestore.com/Resources/Matching-and-other-tube-info/Blue-GlowI have this in pdf format if anyone wants a copy