I just stuck a '50's Chelmer (mullard) CV491 (12AU7 equiv.) in my AirTight amp, which tends towards neutral without being cool, and the expansiveness is luxurious, silences energized with presense...you know, Ralph, kinda like I recall your pre's sounding...(the rest in amp are: WE300Bs, RCA red letter 12BH7s, Natl Union 5u4)
My pre, a Joule LA200, comes stock with NOS tubes (a single Sylv green letter 5751 with a Sylv 6350 follower, GE 6EA7s and Russian OA2s in P/S), but I'm not sure that's unethical. Maybe sticking a CV491 in a stock unit would be that, but not a Sylv green letter - I think it depends on the circuit tube complement and the context, i.e putting the Sylv's in a circuit that needed five of em' might be disregarding the customer, but, on the other hand, paying for Kondo sure better get me primo NOS tubes with readily manuf-obtained back-ups! If not too many LA200/150s are manufactured, it outta work out over twenty years, a reasonable life for a tube unit, I would think.
Atmasphere is certainly right about the regulation, and others are right about the balance of tube characteristics when designing a unit. I just replaced the NOS GE 6EA7s in my P/S with some sweet-looking equiv's, Sylv 50s brown bases. Should be killer, right? Nope - collapsed into indistinct euphonics. Will a Sylv D-getter 6350 sound better than the the Sylv yellow letter I have now as stock? A green letter sq-getter Sylv 6350 that I plopped in yesterday had better dynamics but zero involvement, and the deepest field clapping went from flesh to distant crackles...I sub'd a world-beater Mullard U52 rectifier in for the 5U4 in my amp and everything went to compressed mush...
It all depends. NOS tube rolling IS a mine-field of gas leaks, unmatched sections, bad sellers, etc. but you do get better at it over time.
And, manufacturers are pretty good at finding a balance, if they have good ears to match their technical abilities, in current production tubes.
With that said, however, it has been my experience, that regardless of the pitfalls, an expeirenced hand can balance a sound further towards meaning/truth/beauty, and its perception, using NOS tubes. Which is the foundational reason that people go to them, I assume.
My pre, a Joule LA200, comes stock with NOS tubes (a single Sylv green letter 5751 with a Sylv 6350 follower, GE 6EA7s and Russian OA2s in P/S), but I'm not sure that's unethical. Maybe sticking a CV491 in a stock unit would be that, but not a Sylv green letter - I think it depends on the circuit tube complement and the context, i.e putting the Sylv's in a circuit that needed five of em' might be disregarding the customer, but, on the other hand, paying for Kondo sure better get me primo NOS tubes with readily manuf-obtained back-ups! If not too many LA200/150s are manufactured, it outta work out over twenty years, a reasonable life for a tube unit, I would think.
Atmasphere is certainly right about the regulation, and others are right about the balance of tube characteristics when designing a unit. I just replaced the NOS GE 6EA7s in my P/S with some sweet-looking equiv's, Sylv 50s brown bases. Should be killer, right? Nope - collapsed into indistinct euphonics. Will a Sylv D-getter 6350 sound better than the the Sylv yellow letter I have now as stock? A green letter sq-getter Sylv 6350 that I plopped in yesterday had better dynamics but zero involvement, and the deepest field clapping went from flesh to distant crackles...I sub'd a world-beater Mullard U52 rectifier in for the 5U4 in my amp and everything went to compressed mush...
It all depends. NOS tube rolling IS a mine-field of gas leaks, unmatched sections, bad sellers, etc. but you do get better at it over time.
And, manufacturers are pretty good at finding a balance, if they have good ears to match their technical abilities, in current production tubes.
With that said, however, it has been my experience, that regardless of the pitfalls, an expeirenced hand can balance a sound further towards meaning/truth/beauty, and its perception, using NOS tubes. Which is the foundational reason that people go to them, I assume.