On Sun, 03 Apr 2011 20:09:10 -0700, David Nebenzahl
wrote:

So where does that purplish glow come from? I've seen it.

Impurities in the glass envelope or gas in the tube.

If gas, take an anti-acid tablet and you should be fine in a few
minutes.

http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm
Scroll down to:
C. Blue Glow -- what causes it?
for more details.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558