I personally do not like the sound of most high-powered pentode and tetrode tube amps. Many sound much more brittle and dry than good solid state amps. Notable exceptions to me are some OTL amps.
Most solid state amps these days do not sound grainy, brittle or thin to me--common descriptions given to tube sound in the past. Where they are often lacking is in dynamics at lower volume--compared to a good low-powered triode tube amp they sound lifeless and lacking in immediacy. There can also be a "mechanical" quality to the sound that comes from a slight artificial edge to the attack on all notes and a lack of the subtle variation in attack and decay of notes that one hears with better tube gear. With suitably efficient speakers, I prefer low-powered tube gear. For speakers needing more power, I like OTL tube amps, followed by solid state and then followed by high-powered tube gear.
Most solid state amps these days do not sound grainy, brittle or thin to me--common descriptions given to tube sound in the past. Where they are often lacking is in dynamics at lower volume--compared to a good low-powered triode tube amp they sound lifeless and lacking in immediacy. There can also be a "mechanical" quality to the sound that comes from a slight artificial edge to the attack on all notes and a lack of the subtle variation in attack and decay of notes that one hears with better tube gear. With suitably efficient speakers, I prefer low-powered tube gear. For speakers needing more power, I like OTL tube amps, followed by solid state and then followed by high-powered tube gear.