If you take the cover off you can see both the Bybee Rail and the Audio Magic Pulse Gen ZX (they have little manufacturer's badges on them); of course that doesn't tell you anything about their contribution to the sound, if any.
So if you're interested you have lots of possible tube upgrades/improvements; while the Sophia/Philips combination is likely the best of tubes in current production (I have both although they are back in their boxes at this time), there is a world of NOS tubes that significantly outshine these, though at a price.
So if you're interested you have lots of possible tube upgrades/improvements; while the Sophia/Philips combination is likely the best of tubes in current production (I have both although they are back in their boxes at this time), there is a world of NOS tubes that significantly outshine these, though at a price.