They are two different tubes. The NOS tube was made in the US in the 50s and 60s, the current tube is made in Russia and only shares the branding with the old tube. The factory in Russia pays someone for the use of the Tung Sol name and others like Mullard.
I think it would be unlikely that you would get an improvement in sound equal to the increase in cost. Unless any improvement at any cost is worth it to you, I'd stick with the current production Tung Sol.
I think it would be unlikely that you would get an improvement in sound equal to the increase in cost. Unless any improvement at any cost is worth it to you, I'd stick with the current production Tung Sol.