Tube amplifiers are traditional, and many audiophiles feel that tube monoblocks are the best amplifiers around. However, the price for good quality tube gear is high - with the exception of some cheap Chinese-made amplifiers, a full tube setup can cost hundreds and hundreds of dollars. Is the extra cost worth it?
In a word - no.
Tube amplifiers are inherently superior to transistor amplifiers by nature, but with the exception of some really high-end tube amplifiers, the number of compromises that must be made generally results in poorer quality sound for the dollar. Furthermore, many faults of transistor amplifiers can be overcome by simple good design.
For starters, tube amplifiers run at high voltages - often 300v or more - and are very inefficient. This means that power supplies are expensive, and the output power is generally very low. The price of a tube is also far greater than that of a transistor, while due to the complexity, the tolerances are also far more loose.
Furthermore, because they're power hogs and expensive, less of them are used. A tube amplifier often has only one or two stages for the pre-amp and power amplifier, making compensating for the non-linearity of tubes - which is often very high - a difficult task.
However, the #1 problem with tube amplifiers is in the output transformer - the device that allows the high-voltage low-current output of a tube amplifier to drive an average pair of high-current low-voltage speakers. These devices work like any other voltage-to-current transformer, but they must work equally well at both very low and very high frequencies - a difficult task indeed.
While it is possible to build a transformer that will work at frequencies from 20hz to 20khz without distortion, most tube amplifiers make compromises to cut costs - such high-end transformers can be hundreds of dollars apiece. Many transformers do not function properly at lower frequencies, or have internal inductances that eliminate higher frequencies.
As a result, most tube amplifiers - I.E., those that cost less than $500 after including the preamp and phono stage - simply can't compare to a well-made solid state amplifier for the same price. Distortion is higher, power output is lower, and several other annoying characteristics, like warm-up time, make a good solid state amp a better choice.
On the other hand, tube amplifiers do have their own merits. When a tube amplifier attempts to go above its maximum voltage output and "clips off" the top of the sine wave such as may happen during a loud cymbal crash, the distortion is far lower and less unpleasant than that of a solid-state amplifier. In addition, tube amplifiers - especially "single-ended", or class-A, tube amplifiers - have far less of the crossover distortion found in most solid-state amplifiers.
While there are plenty of stellar tube amps out there, most people simply cannot afford them. Of course, there are plenty of problems with solid-state amplifiers, which I'll go into tomorrow.