Replace the stock JJ tubes with Svetlana 'winged C' or the JJ Blue Bottles. Instead of the 6550 tubes, try KT 88 tubes, again Svetlana are a good beginnng.
The 6sn7 tubes are a bit more work, but you can do much better than the Billington tubes, or so I hear. I am currently using some Sylvania NOS tubes.
This amp is really different and most tube dealers don't have experience with them---especially with an amp that is running this combination of tubes.
The most reputable dealers will make suggestions but will concede they have not precise experience with this amp.
The 6sn7 tubes are a bit more work, but you can do much better than the Billington tubes, or so I hear. I am currently using some Sylvania NOS tubes.
This amp is really different and most tube dealers don't have experience with them---especially with an amp that is running this combination of tubes.
The most reputable dealers will make suggestions but will concede they have not precise experience with this amp.