| JAN stands for "Joint Army Navy", that use totally different numbers for almost all common tubes. The very same 12AU7 in a military number may be referred to as a 6189, or a 5814A, but it's just the same as a 12AU7 tube. Military tubes will usually have "JAN" printed right on the tube along with the tube number, or, a military tube may also have the letters "WA" following the tube number, for example 12AU7WA. This is not a different tube, but rather a military tube. Military tubes are usually built better to withstand the rugged conditions that they may be put through. They also usually have been put through a "burn in" period before being boxed and labeled for military use. You may see a burn spot on the silver part of the tubes, which is called the “flashing”, that may give the tube a used appearance, but is usually just a sign that the tube was burned in before being put into use. It does not mean the tube is used. A vacuum tube is most likely to fail, if it's going to fail, in the first 48 hours of use, and this is one of the reasons that military tubes are burned in. It also stabilizes the tube electronically and burns up any air or gasses that don't belong in the tube. |
