Sounds great with G12M-25 Greenbacks.
My suggestion is to only use one bright switch at a time. Not both. Engage one to the left and leave the other in the center. Then, whichever bright is to the left, drop the gain for that switch down below 12:00 (I like it around 10:00), while running the other gain higher past 12:00 somewhere to taste (the gain knob over the switch left in the center). Then run everything else to taste. But I personally like the presence around 10:30, Depth to taste (but run opposite bass. So if bass is high, depth is low and vice versa), mids very high (like 2:30 or 3:00), and treble around 11:00. Master to taste. Those are my preferred settings regardless of clipping switch in '80s or modern. I never use the amp with the diode clipping off.
Speakers make a huge difference. The amp gets along best IMO with Greenbacks or similar.
While both gains and bright switches are technically the same, there is a slight sonic difference to which one you use. I find V1 to be a bit brighter than V2 in every amp of this type. Mostly because each switch affects a different gain stage. And V1a tends to be slightly brighter. So play around with which bright switch you engage to the left along with dropping its corresponding gain knob.
The bright switches do less and less the higher you set the gain. That's why you should reduce the gain over whichever bright switch you use and then raise the other gain to compensate.
I don't like the bright switches to the right (treble boost). I prefer one of them set to the left (mid-range boost). The Chupa is a bright amp and too much bright switches + presence + treble + V30 speakers = harsh and fizzy. Everything in moderation.
I've played around with tubes as well. I prefer JJ E34L or NOS RFT EL34. Either one, biased cold. Around 60%. The amp will get tighter and meaner and less fizzy.
