Tube amps have one pretentious
use and three good
The pretentious use is in stereo equipment, or in a CD player. Yes, people really make CD players with tube amps. Or at least, there was a company that did it 4 years ago when I read about it in the LA Times. Some audiophiles like to say that a tube amp gives a warmer, more ambient sound than the harsh noise you get from those--shudder--silicon things. However, it has been shown on more than one occasion that you can get great tube amp sound that can fool the pros at a transistor amp price by just putting a low-ohmage resistor between your amp and your speakers. Or, you can buy a graphic equilizer for even more control.
The three good uses are:
- Amplifiers for guitars and other analog electric instruments. Why tube amps? Because when you crank up the volume on your guitar, the output will start touching the rails of your power supply. A transistor amp will just slam into the upper rail, putting a sharp corner on the output that will create all sorts of nasty high frequency sounds that the ear hates. A tube amp will cut out more gracefully, approaching the upper limit asymptotically, and sound much warmer.
- High power. Tube amplifiers are much more efficient than transistor amps. This is a good thing when you are a radio station broadcasting with megawatts of power.
- Customization. If you want, you can create your own vacuum tubes with custom plates and leads that will have their own funky type of nonlinear response in the range you're interested in. Try that with a transistor, and you'll need to invest a few million before you get something you like.