Sugarbrie's advice in his first sentence is right on the money. I have found that well-tested NOS tubes sound vastly superior, and have had a far longer life, in my Jadis equipment, but keep in mind that the stuff I have was made in the late 80s and designed way before that around the then-available Telefunken and MO Valve tubes. A modern piece of electronic equipment is often designed around what's available today, and may well sound excellent with current tubes.
I disagree with the premise, though, that today's tubes are better--I've had too many experiences with new tubes that are supposedly better technology (NOT materials, mind you--that claim cannot be made, in my view) and measure superbly that sounded mediocre and went bad on me in less than 6 months. You have to be careful buying NOS, both in terms of their measurements and their sonic character in your equipment, but at least in my experience they have been worth their cost, both from a sonic and reliability perspective.
I disagree with the premise, though, that today's tubes are better--I've had too many experiences with new tubes that are supposedly better technology (NOT materials, mind you--that claim cannot be made, in my view) and measure superbly that sounded mediocre and went bad on me in less than 6 months. You have to be careful buying NOS, both in terms of their measurements and their sonic character in your equipment, but at least in my experience they have been worth their cost, both from a sonic and reliability perspective.