Why do old tubes sound better than current tubes?

We use tube curves based on the old tubes to design gear. Modern tubes behave slightly differently and most certainly the Russian tubes are NOT direct drop-in replacements for old Mullard designs. Russian Tubes today can handle more current in many designs and require it to sound good.
Much of the NOS stuff is fraud and nonsense IMO, as many of the "better" sounding tubes have no bass or treble thus softening a truly nasty speaker,cartridge or CD player and making an awful system palatable. That is, when the NOS tube is what it has been labeled or is not a completely worn out "pull".

Richard

I picked up a few of the new Genalex 12AX7GENGP tubes from NS and did an audition between them and the 04/60's Telefunken I was using in my C500T.

Guess what -- even though still early, and the Genalex have only 5 hours on them or so since the swap out -- I like what I'm hearing & so, they remain in the MC slots.

Impressive so far folks.

Bob

I picked up a few of the new Genalex 12AX7GENGP tubes from NS and did an audition over a weekend between them and the 04/60's Telefunken I was using in my C500T.

Guess what -- even though still early, and the Genalex have only 5 hours on them or so since the swap out -- I like what I'm hearing & so, they remain in the MC slots.

Impressive so far folks.

Bob

Search the archives, this question seems to come up once a month or so.

There is much more to say about tubes than would fit into a thread. As was mentioned before, some tubes of days long gone by do have a unique mixture of materials in a pureness you won't find anymore today.
But in Audio it all comes down to the individual judgement of the respective listener/owner about what set of tubes he/she like BEST in a specific piece of equipment under certain circumstances ( circuit, matching with other components etc.).
There is no rule - there is no universal guideline. I for one do look for very specific mechanical criteria in tubes (and tube-types..) I use in amplifiers, because I know about certain direct links between sonic performance in a given circuit and specific mechanical/architectural circumstances in a tube. And this too is depending whether I use them as plate-follower, in SRPP mode, input-, driver- and/or phonostage-tube.
In the very end it always come down to what YOU do like best.
That is all that counts.
There is no BEST tube (type or version) out there.
There is a selection of great tubes for each specific purpose.
NOS or NNS - you will find good and great tubes in both camps (but you are likely to find a wider selection in the NOS-camp .... ;-) ..... ).
Try and enjoy.