It is very difficult to find tubes from a NOS Production Period such as the from the 60's Period, that are perfectly matched for the purpose of being used in a Phonostage.
I have Siemens and Mullard Brands which took months of searching and arranging a purchase condition where if a Tube did not measure to a certain level I was allowed to return it.
I got there in the end, one Tube came from Japan ands another from Germany to make a matched pair.
Tube dealers will supply tubes that will produce music and have a decent usage life.
To get Two Tubes with the Four Halves across the Two Tubes all measuring close and above manufacture Spec' is a challenge for certain era's of production.
This is where the real magic is to be found for a usage in a Phonostage, fortunately, these same owned Tubes are transferrable to a used DAC as well.