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How is a tube amplifier different from a solid state amplifier?

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How is a tube amplifier different from a solid state amplifier?

Most consumer audio equipment today uses solid state transistors to amplify your source level audio and drive a pair of speakers with sufficient power to desired listening levels. There's nothing wrong with solid state amplifiers; they are efficient and inexpensive and if designed well can be outstanding in quality. In fact, I may offer a few custom made solid state options at some point myself! Many people will choose to buy a solid state amplifier from an electronics retailer or specialty audio supplier and can expect a long-lasting, low-maintenance device that makes their music sound good. Some solid state amps use a switch-mode power supply that uses high frequency pulses of current, helping keep the device physically small. Transistors have very high levels of gain and left uncontrolled would be unusable and would have high amounts of harmonic distortion, so significant negative feedback is used in the circuit design. Solid state amps typically are higher power devices sometimes up to 100 watts per channel or more so they have sufficient power to drive low-efficiency speakers and enough headroom to avoid unpleasant levels of distortion that would occur if the device were underpowered.

Before transistors were invented, vacuum tubes performed the job of amplifying an audio signal. There is a long and rich history of vacuum tubes as high fidelity devices for audio, and many other applications (you can think of all sorts of things: early computers, military equipment, etc.) I describe how tube amplifiers work on my blog, but the short version is that audio tubes rely on high voltage and a heated element to emit and control a flow of electrons inside a vacuum. They are not perfect in their amplification job ("non-linear") which creates natural harmonic distortion, but this is part of their authenticity and signature sound quality. Unlike transistors, this non-linear amplification is not unpleasant sounding at moderate levels. Tube amplifiers, in particular single-ended amplifiers, are lower-power devices so may typically need higher efficiency speakers. But because of the natural amplification sound and nonlinearity curves, you may be surprised to know that it takes only a few watts of power from a tube amplifier to get high quality sound, unlike a transistor that would have undesirable qualities at low power levels.

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