[R-390] Tubes glow blue

[Roy Morgan]

At 11:24 AM 9/17/2005, Scott Bauer wrote:
>.. If a tube is glowing blue ( besides OA2)
>it should be replaced. ...


Baloney.

Beware, beware!  There are two (three, actually, or more) kinds of blue or 
other color of glow in tubes:

1) The thing is normal and operating properly. It is likely a beam power 
tube and the electrons that don't get glommed by the plate whizz on by and 
hit the inside of the envelope. The *glass* glows.  This condition is 
recognizable because the glow is ON the INSIDE of the glass envelope.

This is not harmful or indicative of any fault or weakness in the tube.

2) The tube has some gas inside (when it should not have much at all).  The 
electrons whizzing toward the plate hit the gas particles and the gas 
glows. This condition is recognizable because the glow in AMONG the tube 
elements, NOT on the inside surface of the glass.

This IS indicative of a fault or weakness in the tube. However, if you run 
the tube for a while, the heat *may* make the getter material glomm onto 
the gas, reducing or eliminating the gas and the glow goes away.

Certain relatively new tubes (such as made by the Viac company for 
audiophiles) have special getters attached to the plate, which plates run 
so hot as to heat up the getter device and activate it further to glomm 
more gas.  These unusual getter devices may be washer- or ring- shaped 
things that are seldom seen in old tubes.

Notes on terminology:

"whizz" to travel at a high rate of speed. In the case of electrons 
travelling from a cathode to somewhere else, accelerated by the 
electrostatic potential difference between the electron and the somewhere else.

"glomm" a special term borrowed from the seller of the engagement ring now 
in our family, who would sternly caution the Groom while He was examining 
candidate diamonds, "Don't Glomm the Stone!" -meaning grab onto, cause the 
brilliant to become dull, or otherwise mess up by attachment of dirt or 
whatever.  Very used tubes such as transmitting tubes, power tubes such as 
807's, 6550s, KT-88's and the like can sometimes be identified as being 
past their useful life  because the getter material flashed upon the inside 
of the glass has turned brown or discolored.  The shiny stuff has become 
glommed by sucking up too much gas.

"getter" any material or structure inside a tube intended to glomm the gas.


Notes on Good kinds of Glow.

Any of the following tubes are supposed to glow and if they don't, 
something is wrong:

  - any voltage regulator or voltage reference tube.  Voltage reference 
tubes often both have stuff on the inside of the glass (intentionally) and 
glow very faintly anyway, so you may not see the glow easily

  - Rectifiers of the mercury vapor or Xenon gas containing sort.  These 
include 872A, 866, 866A, 816, 3B28, 3B32.  (The 0Z4 was an abomination of 
design and manufacture, was intended to save power in car radios, almost 
never lasted very long, had metal envelopes anyway, and should be discarded 
instantly whenever encountered.)

  - gas relay tubes such as the 2020, 2D21 and the like.

  - Most thyratrons.



(Scott continutes...)
>  Something must be wrong here. These are all NOS, NIB shiny
>new tubes.

Nope, possibly nothing is wrong. If the blue is on the inside of the glass 
everytjhing is just fine. Enjoy using your excellent new tubes.

>So, for the new tubes is this gas burning off? A burn in? I have only
>noticed this with 6AK6's. No others.

The gas may have been glommed by the getter material, or the plate.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan at nist.gov --