NOS 12ax7's sound different than new ones, that is a fact. Wether or not they sound better is subjective. This brand of new 12ax7 sounds different than that brand of new 12ax7, so look at old tubes as just that, another manufacturer that just happens to not make tubes anymore. You are basically asking if everything called "chocolate cake" tastes the same.
Dont go through the process of getting hung up on which NOS tube is "best". I have a favorite NOS tube that I reach for first, but what works really well in one circuit doesnt work so hot in the next, so where a phillips migght rule the earth in one gain stage, an amperex might be bettter in a differently designed amp. If you look on ebay, people pay ALOT of money for old tubes, before you go and put yourself in that position, make sure that the brand you are buying actuallly sounds really good in what you are intending to use it. Sure, telefunken tubes sound pretty good but often you can find something just as good if you are not using it in hi-fi. Ive seen people put $100 preamp tubes in guitar amps and I think you are really getting into diminishing returns at that point, you dont need to spend that kind of money on a distortion generator, the $30 amperex can sound just as good as the $100 telefunken in the preamp section of a bassman...
My experience tells me that tube brands are very application specific. Sometimes you want a mushy sounding tube, sometimes you want a stiffer sounding tube, but the short answer is that tubes most certainly sound different.
dave
