Discolored getter flashing (brown or black marks) does not mean that a tube was used. This fiction is believed by both uninformed buyers and seasoned tube jockeys. This myth seems credible because some new tubes have perfect shiny mirror getter flashing; therefore the assumption is that brown or black stains in the getter flashing must indicate a used tube. The myth says that the more brown/black discoloration, the “more used” the tube is. Wrong.
The purpose of the tube getter and flashing is to remove gas inside the tube envelope during manufacture. This discoloration myth can be quickly debunked by reading the article in Electronics magazine, October 1950, entitled “Getter Materials For Electron Tubes”. The article explains that if the getter is vaporized very slowly during the manufacturing process, “the first barium atoms evaporated will absorb the gas present so that the remaining getter is deposited in a very high vacuum, exhibiting a shiny mirror.” If the getter was flashed very rapidly during manufacturing, then “the getter mirror will be discolored due to the dispersion of the barium.” The article then explains that the discoloration “does not mean that the getter is contaminated, but merely that the deposit is finely divided and therefore absorbs light.”
Several photos of NOS tubes below demonstrate this myth. Likewise, I provide photos to demonstrate how the flashing looks when a tube is actually used. Let us proceed…
Examples of Perfect NOS tubes that have Brown/Black getter flashing marks:
Click on each photo below to enlarge.
My first example is from a case of 100 mint NOS NIB NEW Philips 12AX7WA US Military surplus audio tubes.
Highest quality inventory, and my personal preference in my own McIntosh amps. This case was factory sealed until opened by me to sell the inventory.
The next example is from a case of 100 mint NOS NIB NEW Philips 6922 US Military surplus audio tubes.
This case was also factory sealed and was opened by me for purposes of writing this article.
The third example is from a sleeve of beautiful NOS NIB NEW General Electric 5687WB tubes.
In all of the above examples, you see perfect NOS NEW tubes that were never removed from their boxes until I photographed them for you. They all show dark brown/black discoloration. This getter flashing discoloration is from the gas extraction process during manufacturing, and means nothing. This discoloration is a normal part of factory production and tells you nothing about new vs used or the quality of the tube. It only tells you that the manufacturer used a very rapid flashing process, and from the Electronics magazine article, that means “merely that the [flashing] deposit is finely divided and therefore absorbs light.”
Can the getter flashing show whether a tube is used or defective?
Yes (sometimes).
A used tube may show a smoky-clear wearing away of the flashing color (or sometimes orange discoloration), and a rainbow effect around the flashing area. However, a rainbow without a noticeable wearing away of flashing color is not a reliable indicator.
Example #1: Tung-Sol (Leslie branded) 6550 Coke bottle tube. This tube is used, and a rainbow can be seen around the getter flashing. The flashing is losing color.
Example #2: RCA 5U4GB tube. This tube is also used, and shows both a smoky-clear wearing away of the flashing color and rainbow effect.
Example #3: pair of British Amperex 6CA7 – EL34 audio tubes. These tubes are used, and have orange hue flashing discoloration and the rainbow.
Please understand that just because these tubes are used, this does not mean that they do not test good. They may test excellent (and in fact, all of these examples test very good). Again, the getter flashing does not tell you anything about how the tube will perform. The pair of Amperex EL34 shown above is the best sounding pair of EL34 that I have owned.
Example #4: A milky white discoloration of the getter flashing indicates that the tube has lost its vacuum and is therefore defective.
With this information, you can better understand the tube getter and flashing. In summary, Brown and Black flashing discoloration is normal part of manufacturing. It does not mean that someone sold you “used tubes”. It does not mean that the tubes are bad. It means nothing. Smoky-clear wearing away of the flashing, rainbow, and orange hue indicate usage but tell you nothing about condition. A milky white getter flashing indicates vacuum loss and total defect.
regards,
Bob Putnak.
eBay ID = rjputnak© 2008. All rights reserved.