The answer is quite simple, yes, tube amplifiers generally sound louder then a solid-state alternative but the generality of the question is never directed to the possibility of producing higher sounds. The tubes have special magic with the tones they produce that makes them addictive to our ears. If you can connect it to a suitable speaker, the amplifiers with tubes are capable of producing a live and real sound in a way that the transistors will never do. For example, to reproduce the middle frequencies, which is where most of the music resides, there is no better option than a tube amplifier. These manage to transmit the sound of the voices and strings with a silkiness and detail of harmonics, making the timbre of each instrument produce more lively sounds. The tubes transmit the warmth of the middle rounds with a special musicality.
Another aspect where a tube amplifier stands out is in the high frequencies which do not reach the point of aggressiveness that one easily hears in the solid-state amplifiers. The sound of a cymbal in a tube system has a duration in time greater than the one coming from a solid-state amp. The difference is that in the tube amplifier that sound extends through thousandths of a second more than what can be heard coming out of a solid-state amp in which the sound is rather dry. This fact makes tubes a more realistic choice. As an example, imagine hitting a cymbal, you can hear the vibration of the metal for a long time and it would not end at the same moment as it would in a solid-state amp.
Another great feature of the tubes is their ability to create a much larger soundstage. It is understood by “soundstage” the sound of the environment where the recording has been made. That is information that helps us to perceive the musicians within an acoustic environment, within a space whether large or small and also allows us to locate the source of a sound within that space. The tube amplifiers have that peculiarity of putting us in front of the musicians and creating a space and a feeling of “air” between the players in a more credible way. To simply put it in a short sentence; It brings us closer to reality.
A low-cost, low-power tube amplifier also has these characteristics that distinguish it from solid-state tubes. An inexpensive and low-power tube amplifier usually has an undefined and somewhat loose bass, but this negative characteristic is overcome and “forgotten” by the beauty in the reproduction of mediums and highs and by having that kind sound characteristic of its lineage.
Remember that not everything is wonderful in this sweet and friendly tube sound. There are designs and situations in which an excess of these characteristics ends up imposing and coloring the sound in an undesired way. The idea is that an amplifier does not impose its sonorous seal, or in any case that it does so in a very subtle way. Ideally, an amplifier should reproduce what is recorded without altering the sound. Nobody wants a too big and slow sound that is an exaggerated feature of some old amplifiers.
On the other hand, solid-state amplifiers, as we have indicated, have an advantage in bass reproduction, these tend to be more precise, defined and faster. The transistor is able to reproduce the initial sound of a string, a key or a percussion hit with more realism given by its speed of response. This characteristic of musical reproduction is known as “transient” and is nothing more than the beginning of a sound, the moment when the nail tears the string or the drumstick and hits the drum, that can be translated as a transit for example. In counterpart there is the term “inter transient” which are the silences between the musical notes, it is very important that the amplifier has the ability to start a note and then stop in an instant and leave that blank space that allows you to clearly appreciate another tone. These two aspects are very well handled by transistors.
Another sound characteristic that distinguishes a transistor design from a valve is the definition of the image. When we listen to a stereo recording, in the space between the two speakers, a sound image is created that is none other than the reproduction of the location of each instrument in the room. This is according to how the sound engineer created it during the recording. Usually, there is some instrument or perhaps a voice located in the center itself, as some instruments are located on the sides and others further away even reaching beyond the outer limit of the speakers. These limits often take on spectacular dimensions due to the excellent acoustics of the listening room. This definition of the image is handled with greater precision in solid-state amplifiers. But in some cases, it becomes very exaggerated and loses realism.