[squarefoot]

Technically speaking there is zero advantage in using tubes instead of solid state when the amp is driven below distortion, that is for listening to music at normal level, and anyone claiming they can hear the difference between a decent 100 bucks class D amp and the most expensive tube amp in the galaxy is lying (probably also to themselves if they bought the latter). However, when tubes are driven to distortion, the waveform is clipped in a much gentler way compared to what is produced by solid state parts, so in a Hi Fi amp those high power peaks would indeed sound a lot cleaner, and in a guitar amp where distortion is looked for by design, using tubes would would produce a much nicer clipped sound, which is even more audible when playing chords. In HiFi amps the problem can be easily solved by designing (or buying) for more power than what is needed, so that the headroom reserve will be used to cope with those peaks without getting into clipping, while using tubes for guitar amps apparently still makes sense. Technology however has progressed a lot since the old days, most parts have become a lot cheaper, and even without resorting to digital manipulation todays solid state pure analog guitar amps can sound great without using tubes.

One important point though: when making guitar amps with newer technologies such as class D, we must redesign everything so that the amp -I mean the power module- will never clip; no matter what we throw at the amplifier main input, the power module must never be driven into distortion because class D distortion is plain awful. That requires a lot of redesign: no more clipping tubes, coils driven into saturation, purposely weak designed power supplies etc, but simply speaking we distort before and keep the level put in order not to distort after. This makes things even more interesting because one builds the guitar sound much before it gets to the final stages, the only further contribution to the sound being the speaker and the cabinet, not the amp module.