Tube factories in China use Russian tube-making technology from the 50's, 60's and 70's. Except for some specialized sector producers like Full music and Valve Art, tubes for the consumer market undergo dubious QC processes - if it works, it's for sale.For how long and how well is irrelevant.

Not so with tubes produced for the military during the 60's, 70's and 80's. These tubes were manufactured to military specifications, had to pass reliability and durability tests, and were graded 'J', 'T', and 'Q'. 'J' was for basic military service applications and is most common, 'T' and 'Q' were for special applications such as avionics; 'T' is not commonly available and 'Q' is rarely seen. The year of manufacture and in most cases the grade, are stamped on the glass envelope. Most have metal bases and are indeed rugged. We very seldom get a throwaway. They come to us packed in bulk crates.