I don't remember which company it was and I think it was back in the
1960's.A company was experimenting with some vacuum tubes for radios and
they claimed the tubes generated much less heat than the other kinds of
regular vacuum tubes for radios.The tubes emitted a blue glow instead of
the familiar red glow of regular vacuum tubes and the company also
claimed their tubes lasted much longer because of much less heat too.I
read about it in a Popular Science magazine back in the 1960's,,, or it
might have been in the late 1950's when I read that article.
cuhulin