Glai:
Rcprince's experience with tubes from his use in the previous response are all good recommendations and are all in the upper crust of the 6922 tube family. There are a wide selection of tubes in this family, spanning from "modest and affordable" to really expensive. You might find it helpful to try a small selection of "affordable" choices to get a taste of the changes you will find in your system. In addition to Siemens and Telefunken, you might want to look closely at the Ameperex family: there are a lot of choices. I have had very good success with carefully selected Brimar ECC88's.
Rcprince's experience with tubes from his use in the previous response are all good recommendations and are all in the upper crust of the 6922 tube family. There are a wide selection of tubes in this family, spanning from "modest and affordable" to really expensive. You might find it helpful to try a small selection of "affordable" choices to get a taste of the changes you will find in your system. In addition to Siemens and Telefunken, you might want to look closely at the Ameperex family: there are a lot of choices. I have had very good success with carefully selected Brimar ECC88's.