Applications
The triode was the first device to provide power gain at audio and radio frequencies, and made radio practical. Triodes are used for amplifiers and oscillators. Many types are used only at low to moderate frequency and power levels. Large water-cooled triodes may be used as the final amplifier in radio transmitters, with ratings of thousands of watts. Specialized types of triode ("lighthouse" tubes, with low capacitance between elements) provide useful gain at microwave frequencies.
Vacuum tubes are obsolete in mass-marketed consumer electronics, having been overtaken by less expensive transistor based solid-state devices. Triodes continue to be used in certain performance sensitive areas such as high-end and professional audio applications, as well as in microphone preamplifiers, electric guitar amplifiers and high power RF amplifiers and transmitters.
Read more about this topic: Triode