What is Blue Glow

From Gruvmyste–(at)–nn.com Thu May 9 23:21:44 CDT 1996
From: Gruvmyste–(at)–nn.com (Doug Haugen)
Newsgroups: rec.audio.tubes
Subject: RE: Blue glow on output tubes
Date: Thu, 09 May 1996 22:13:47
Mime-Version: 1.0
X-GNN-NewsServer-Posting-Date: 10 May 1996 03:11:32 GMT

I wish I was smart enough to come up with this on my own. I’m not.
I quote the Sylvania Engineering Data Service handbook (those
really BIG tube manuals): “Blue Glows are not tube detriments per
se. They are, however, suspects in the eyes of many receiving tube
users for a lack of full understanding of their origins. There are
several types of Blue Glow which can be described as follows:

Fluoresence: this type of glow is usually violet in color and most
noticeable around the inside surface of the glass bulb. It is most
pronounced on power tubes and is the product of electron
bombardment of the glass taking place within the tube. It generally
has no adverse effect upon receiver performance, and in fact, tubes
displaying this phenomenon are particularily good with respect to
gas content.

Mercury Vapor Haze: is a blue-violet glow associated with those
tube types which rely uopn mercury vapor for proper operation. In
such cases, the blue glow should be evident indicating proper
operation.

Gas: produces a blue haze, generally confined to the vicinity of
the mount structure. The proper function of gas types such as
thyratrons, voltage regulator and voltage reference tubes, requires
the presence of this glow as an indication of proper tube
operation. Some voltage regulators use neon instead of argon and as
a result exhibit a pink-orange glow. It is, however a distinct
detriment in vacuum receiving types, where the presence of gas in
large amounts can cause malfunction of the equipment.”

(Slvania Engineering data service, Vol 1, page 23, tab “general
information”, no date given)

This seems pretty definative. I hope it helps!

Doug