@larsman nice choices…I love my Aric amp and he’s such a great guy as well. I have an Aric Super 300B Set amp paired with a Supratek Cabernet 6SN7 preamp. Just a pair made in heaven. I have rolled and researched many 6SN7 tubes. There are many good choices but I keep coming back to my 1952-53 Sylvania 6SN7GT, GTA, WGT versions. They are just magical in my 2 amps. Sylvania makes a-lot of various versions so the best ones , in my mind, are late 40’s-early 50’s short bottle with heavy chrome getter running down the sides and only the parallel T-Plate with rectangular Mica’s.. (NOT THE ANGLES V PLATES). The military versions have extra support rods and brown bases are most common. I feel they sound very similar if not the same. Just my experience and 2 cents. Enjoy the preamp.
Here is an example of a nice pair. https://ebay.us/m/aajZ45