Why are older tubes so much sought after

Just one more comment from the peanut gallery. The Soviets in particular continued to use tubes in a lot of their military equipment long after the US military had moved much of their equipment to solid state. (In fact, they felt vacuum tubes were more resistant to the EMF effects of a nuclear bomb and gave them an advantage in the survivability of their electronics.)

One can get into the endless loop debate of whose military had stricter QC standards for electronics manufacturers (and the US has had its share of equipment procurement scandals over the years) but the military angle alone does not explain the differences in tubes.

Let me try again!

Trelja- Just curious what 7199's you're using. I owned(and modded) an ST-70 for about 15 years and found the Sylvania and Phillips ECGs to be the best. Have you installed a NOS 5AR4 yet? Talk about another revelation! I used a Mullard in that position. Regarding the others' experiences with their un-named NOS tubes of unknown origin: (like everything else in this hobby) Your results will depend a lot on into what these tubes are plugged, their condition/quality, and who is doing the listening(many variables). The best NOS tubes just get out of the way of the music and add or subtract nothing, which is the definition of, "transparency", and you've removed one variable by using them. From there it becomes a matter of taste and/or what may be lacking in the rest of the gear.

Well Albert,the movies,music and entertainers of the 40's,50's,and 60's might have to be included as well -:)

Mil Spec components were usually required to be much better than necessary. That was before cost control became important. Nowadays most military equipment uses commercial hardware whenever possible, which greatly reduces cost, improves (yes) reliability and performance. Also, we have learned to make electronics whose performance is derived from the basic circuit design rather than from reliance on tightly spec'd components and trim procedures.

I am surprised that new tubes are less accurately made. A tube would seem made to order for precision automated fabrication.