Almost abandoned by consumers when, in the 1960s, slimmer, lighter, and more powerful transistor amps came out, tube amplification is back with a vengeance. Long favored by many professional musicians, recording engineers, and audiophiles, the warm sound of tubes makes a perfect foil to the fine-etched sound of today's digital sources. Unlike transistors, tube amplifier circuits cannot be directly connected to a loudspeaker, requiring the addition of an output transformer to 'match' the tube to the speaker. These output transistors are built into virtually all tube amplifiers.
The downside of having this transformer is increased size and weight (don't expect to see a tube-type portable MP3 player any time soon!) but the upside is that, with connections for different types of speakers (2,4,8, and/or 16-Ohms impedance) available, tube amplifiers typically deliver their full power with any speakers. In other words, you don't get as much 'rated' power in a tube amp, but, because of the output transformer, you get all the power you paid for delivered to your speakers; which are an important component of home theater systems, just make sure to use the right connection.
The impedance of your speaker should be printed on a label next to the connection terminal. It will say 2, 4, 8, or 16-Ohms. The output transformer, rare in transistorized amps, is the 'secret weapon' of the tube amplifier designer. It allows for great creativity of design, and with that, a more colorful sonic signature.
Typically not as powerful as their transistorized counterparts, and requiring a little more TLC (tubes wear out), tube amplifiers offer an 'ease' of sound and 'rounder' sound that is hard to duplicate with more modern designs. For those desiring the sonic signature of tube amplification, but who want to replicate live-sound volume, more powerful tube amplifiers have recently been introduced. For the well-healed music lover, they provide the best of both worlds.
If you crave the warm sound of tubes, but you either don't have the deep pockets it takes for a high power tube amp, or you want a 'set it and forget it' maintenance-free system, a tube preamp (often referred to as a control center) may be the answer. Passing your music through a tube preamplifier on it way to a transistorized amplifier often imparts just enough of that special sonic signature, while providing sufficient power for even the most power-hungry speakers. The choice is up to you. Just remember that it's the QUALITY of the design, not the TYPE of design that will determine the sound.