Erfranke, I believe the S-30, like other Atma-Sphere amplifiers, will use only the 6AS7G output tube. Ralph can give you recommendations on specific brands but my best experience has been to buy them directly from Ralph.
As to the 6SN7 input tubes, I am very fond of the Sylvania brand 6SN7GTA and GTB tubes manufactured up until the 1970s. They sound very good in my MA-2 amps.
.
As to the 6SN7 input tubes, I am very fond of the Sylvania brand 6SN7GTA and GTB tubes manufactured up until the 1970s. They sound very good in my MA-2 amps.
.