Single-ended outputs, lacking that cancellation, can have as much as 15 percent total harmonic distortion, mostly second order. Though readily detectable, the effect is not unpleasant, tending to add richness and fullness to the reproduced sound. According to Hayes, it was used deliberately by manufacturers to improve the tinny sound quality of 1940s radios. Fraught as it is with human and technical interest, the controversial audio market is a relatively tiny part of the tube business, which is far larger than most people imagine. In general, at almost any frequency there is a power level above which it makes more sense to use a tube rather than an array of transistors as the final power amplifier.
Microwave ovens are a good case in point.
Radio transmitters are another point of interest in tube country. In building power amplifiers for AM radio transmitters, where the goal is to generate 25 or 50 kilowatts at one or two megahertz, the tendency today is to go solid-state. For ultrahigh-frequency transmitters, which operate above 300 megahertz, tubes still reign supreme. Below about 40 watts, they use arrays of gallium arsenide field-effect transistors. Above that level, it's traveling wave tubes.