Years ago, high-power transistors were supposed to put an end to vacuum-tube electronics once and for all. In consumer audio electronics, this is more or less true, with most audio amplification products based on solid-state devices. But there is a small group of high-end listeners that still support a reasonable market in vacuum-tube-based audio amplifiers And the same is true in the professional music industry, where guitarists make creative use of the harmonic-distortion characteristics of vacuum tubes.
At RF and microwave frequencies, vacuum tubes are still going strong, especially in applications requiring broadband frequency coverage, high power levels, or a combination of both. For example, e2v recently released a pair of extremely broadband mini-helix travelling-wave tubes (TWTs) with bandwidths of 4.5 to 18 GHz and 2 to 18 GHz, respectively. Ideal for applications in commercial and military systems, the broadband coverage makes it possible to replace several tubes with a single device. And, while solid-state devices are capable of providing perhaps 1 W or so of broadband power across similar bandwidths, solid-state devices capable of tube like power across broad bandwidths are still in the formative stages.