Grumpybb@aol.com provided a perfect answer. I would like to add that there are several countries like Yugoslavia, Russia and China that manufacture new tubes. The reason the NOS tubes are so sought after is that many were designed and manufactured to military specifications. It was not that long ago that tubes were as important to military forces around the world, as computers are today. Obviously, any product having that much importance to national security was built to standards that cannot be copied today. The budget for parts of the space shuttle ($600.00 hammer or whatever) is a perfect example. The subject of NOS tubes is complicated, and some of the new tubes manufactured today are equal to NOS. Many others cannot be duplicated, and therefore are available only as the original NOS. Unfortunately, this is a tube by tube and component by component test as to what is the "best." Long life and reliability not even taken into consideration! This would not be a bad thread for other Audiogon posters to discuss their favorite tube choices. You could post what worked the best, where is was used (equipment and position) and what it replaced.
