Thank you. Do you know for a fact that all 4 small tubes are used in line section?
The Dialogue 2 has HT bypass inputs. This means that its amp section can be used separately by running an outboard preamp into. I'm guessing that one pair of small tubes is for the line section (either gain or buffer), and one pair is for amp drivers.
This is why I ask the question. If I use the amp section only, the line stage is not in play and I can use any ol crap tubes in there, and I only need to concern myself with rolling tubes in the amp section.