Tube 50W "screams" more pleasant than SS 50W. On the lower volume levels they will sound absolutely the same in terms of loudness. The low (10x less than transistor's) output resistance of the tube allowes to draw the maximum current onto the speakers but needs to be matched with the speaker's impedance by means of matching output X-former. Thus even "under-powered" tube amps(i.e. bellow speaker power requirements) can successfully control the driver's coils. On my experience, low-powered SS amps(unless it's Pass Labs Aleph series) can't controll speakers. The beat of drum continues longer, bass isn't tight and deep.
SS designes are soffisticated and require a large amount of negative feedback(upto 30...40dB) to bring the circuit elements(transistors) onto linear operation on the audiable freequencies decreasing dynamic performance that is so necessary for orchestral music. Bringing SS amps to the peak powers will certainly drammatically change the output freequency bandwidth curve and the amplitude will reach non-linear area of output Volt-Amp characteristics(clipping)
Since tubes have linear output Volt-Amp characteristics its designes use minimalistic circuits and very often with no feedback(but for real feedback is needed to increase the freequency bandwidth). The signal is more transperent and open when the circuit path is minimal.
SS designes are soffisticated and require a large amount of negative feedback(upto 30...40dB) to bring the circuit elements(transistors) onto linear operation on the audiable freequencies decreasing dynamic performance that is so necessary for orchestral music. Bringing SS amps to the peak powers will certainly drammatically change the output freequency bandwidth curve and the amplitude will reach non-linear area of output Volt-Amp characteristics(clipping)
Since tubes have linear output Volt-Amp characteristics its designes use minimalistic circuits and very often with no feedback(but for real feedback is needed to increase the freequency bandwidth). The signal is more transperent and open when the circuit path is minimal.