Such deposits exhibit higher efficiency than the bright deposits.” This condition does not mean that the getter is contaminated, but merely that the deposit is finely divided and therefore absorbs light. If vaporization is carried out in the inert atmosphere of a rare gas the condensed deposit will be black, resulting in a dispersal getter. If flashing is done very rapidly, however, the getter deposits in a rather high vapor pressure and the getter mirror will be discolored due to dispersion of the barium. If the getter is vaporized very slowly, the first barium atoms evaporated will absorb the gas present so that the remaining getter is deposited in a very high vacuum, exhibiting a shining mirror. The appearance of the condensed getter deposit depends upon the vapor pressure in the tube at the time of flashing. The barium vapor condenses on the cold surface opposite the getter material, usually on the envelope of the tube. “Flash getters are outgassed at temperatures between 600 and 700 C, usually by r-f heating from the outside of the tube, and flashed at temperatures between 900 and 1,300 C. We also have the entire article available for download. It’s very long but below is an excerpt about the getters you will see in most common audio tubes. Here in Photo 3 we show various colors of healthy getters.Īn article by Electronics Magazine published an in-depth article about tube getters in October 1950. It is not a burn at all but rather a product of how fast the flashing was done. Inexperienced or misinformed folks may think a black color is a burn mark. The shade of gray can vary from chrome-like to black. Regardless, the getter flash is what indicates there is a good vacuum in the tube and that no air has leaked inside. There are even tubes that have multiple getters on the top and sides. Most tubes have the getter flash at the top of the bottle, but some have it on the side or even bottom of the bottle. The getter or getter flash is the silver/gray coating seen on the glass of a tube. A tube showing this needs to be replaced. There could be a small crack in the glass or a leak around one of the tube’s pins. However, if you see bluish/violet glow around a single element such as a wire for example, it could indicate an air leak into the tube. To summarize, almost any blue glow you see inside a tube is perfectly fine and will not cause any problems in your amplifier. It is, however, a distinct detriment in vacuum receiving types, where the presence of gas in large amounts can cause malfunction of the equipment.” Some voltage regulators use neon instead of argon and as a result exhibit a pink-orange glow. 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. GAS (Photo 2)- produces a blue haze, generally confined to the vicinity of the mount structure. (Note from thetubestore: Mercury Vapor tubes are rare and almost never found in common guitar or hifi amplifiers) In such cases, the blue glow should be evident indicating proper operation. MERCURY VAPOR HAZE - is a blue-violet glow associated with those tube types which rely upon mercury vapor for proper operation. It generally has no adverse affect upon receiver performance, and in fact, tubes displaying this phenomenon are particularly good with respect to gas content. It is most pronounced on power tubes and is the product of electron bombardment of the glass taking place within the tube. There are several types of Blue Glow which can be described as follows:įLUORESCENCE (Photo 1)- this type of glow is usually violet in color and most noticeable around the inside surface of the glass bulb. They are, however, suspects in the eyes of many receiving tube users for lack of a full understanding of their origins. In the 1960’s Sylvania printed the following article:īlue Glows are not tube detriments per se. This was also seen in tubes from the golden age of vacuum tube production. Photo 1 shows a tube with a healthy blue glow. In fact, many tubes have a blue glow, especially modern tubes. Thankfully, it is rarely a sign of a defect at all.
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