First, NOS tubes can produce more of an audible effect as the quality and tweaking of your system improves. Same as a car...you can feel the difference that a few pounds of tire pressure produces in say a Ferrari. A Neon or Focus, and you couldn't tell if the tires were only inflated to half pressure!
Second, the purity of chemical compounds used on the cathodes is much better than on modern tubes. The vacuum isn't as hard on modern tubes. The tolerances [especially on the grid wires and their windings] are nowhere near NOS tubes. I think it was RCA that determined that the location and bend angle of the grid wire terminations could effect the performance. When their manufacturing plant closed, file cabinets full of decades worth of irreplaceable engineering data were just left in the abandoned buildings...generations of knowledge lost forever. Also, I believe that EVERY NOS tube was burned in for 100 hours at racks in the plant.
That being said, NOS tubes were not made with the audiophile [came later on] in mind. It is important to have someone test [and match, if necessary] the NOS tubes, as some can be quite noisy, especially if used in a MC phono preamp. Andy Bowman at Vintage Tube Services is the best, period! Chinese tubes seem to be VERY quiet, but they will not last all that long, compared with an NOS. But at the cheap prices for Chines tubes, does it really matter?!
Actually, the only demand for tubes is from audiophiles [not really a market, in the big scheme of electronics], R.F. applications, and guitar amps, most of which use a 6L6, so these 6L6's will be produced forever!
Second, the purity of chemical compounds used on the cathodes is much better than on modern tubes. The vacuum isn't as hard on modern tubes. The tolerances [especially on the grid wires and their windings] are nowhere near NOS tubes. I think it was RCA that determined that the location and bend angle of the grid wire terminations could effect the performance. When their manufacturing plant closed, file cabinets full of decades worth of irreplaceable engineering data were just left in the abandoned buildings...generations of knowledge lost forever. Also, I believe that EVERY NOS tube was burned in for 100 hours at racks in the plant.
That being said, NOS tubes were not made with the audiophile [came later on] in mind. It is important to have someone test [and match, if necessary] the NOS tubes, as some can be quite noisy, especially if used in a MC phono preamp. Andy Bowman at Vintage Tube Services is the best, period! Chinese tubes seem to be VERY quiet, but they will not last all that long, compared with an NOS. But at the cheap prices for Chines tubes, does it really matter?!
Actually, the only demand for tubes is from audiophiles [not really a market, in the big scheme of electronics], R.F. applications, and guitar amps, most of which use a 6L6, so these 6L6's will be produced forever!