Last night, while hosting a big blind listening test, we decided to compare a few 12AX7 tubes.
We'd started our evening with old-stock 60's black plate RCA and Raytheon pair. Just for fun I put in a pair of Sylvania Gold Label, Gold Pin tubes with low noise testing from the manufacturer. These tubes are really not available from any dealer, anywhere -they are ultra rare, I just happen to have a few quads. (The lettering is real gold leaf! I think they may have originally been made for Amperex.) Anyway, we put in the pair and oh my, oh my!! I put on a record of J. Heiftz and Brooks Smith doing a recital at the Dorthy Chandler pavilion and you would swear that the Steinway Grand was sitting in your living room! Wow!
The Mullard 12AX7 long plates have long been my favorite for phono stage, but these Sylvania Gold were definitely their equal.
For phono stages, the GE 5751 receives high recommends as well. It is a sleeper tube equal to the Mullard, but often at a better price.