The KT88 is a beam tetrode

Beam tetrode

A beam tetrode is a type of vacuum tube specially designed to produce greater output power than a similar pentode...

/kinkless tetrode (hence "KT") vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

 for audio

Audio frequency

An audio frequency or audible frequency is characterized as a periodic vibration whose frequency is audible to the average human...

 amplification

Amplifier

Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...

.
The KT88 fits a standard eight-pin octal socket and has similar pinout

Pinout

In electronics, a pinout is a cross-reference between the contacts, or pins, of an electrical connector or electronic component, and their functions.- Purpose :...

 and applications as the 6L6

6L6

6L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency...

 and EL34

EL34

The EL34 is a thermionic valve or vacuum tube of the power pentode type. It has an international octal base and is found mainly in the final output stages of audio amplification circuits and was designed to be suitable as a series regulator by virtue of its high permissible voltage between heater...

. Specifically designed for audio amplification, the KT88 has similar ratings to the American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 6550 which was designed for use as a servo amplifier. It is one of the largest tubes in its class and can handle significantly higher plate voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

s than similar tubes, up to 800 volts.