Why don’t tube amps sound like tubes anymore?

I have heard sometime ago that the reason older tube amps sound so tubey is due to higher levels of distortion when compared to newer designs.

This is partially true. Its the 2nd and 3rd harmonics that are in question- together with a lack of higher ordered harmonics. Older amps tend to have a significant amount of the 5th thrown in; many newer amps do too. But some amps have less 2nd harmonic these days- if the amp is fully balanced and differential from input to output, the primary distortion component will be the 3rd due to a cubic non-linearity, whereas the 2nd results from a quadratic non-linearity. Amps based on the 3rd harmonic tend to have less distortion overall with higher orders falling off at a faster rate as the order of the harmonic increases. These types of amps simply were not in use back in the 50s and 60s.

I was thinking about this more and what I like about my amp is not that it's warm and "tubey". It's that instruments and voices have more tonal color and saturation. They are more dimensional and seem more "there". That about sums it up to me.

Moscode-...

@jond. Yeah this is what singled ended amps do for me as well whether tube or ss.
If you get the opportunity listen to the Pass stuff. I believe his I25 integrated is s.e. First set of watts run A so it does not get too hot.
Also, there’s the French company "Valvet" that also gives this impression to me and that is also an ss unit.
Tough to find however.

Maybe it's the switch to solid state rectification in the power supplies.  The old amps that used tube rectification, chokes and less capacitance had more sag, which added more warmth to the sound.