KT88

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KT88 vacuum tubes, or valves, are used in the power sections of tube amplifiers. The KT88 is a beam (kinkless) tetrode tube, fitting a standard eight-pin (or Octal) socket, with similar pin out and functions as the more familiar 6L6 and EL34. It was manufactured in the U.K. by G.E.C, also labelled as IEC/Mullard, and, in the U.S., Genelex Gold Lion.

It is a larger variant of the KT66. It is specifically designed for audio amplification and, while it has a similar ratings, it is quite different in perceived characteristics from the American 6550 tube, which was designed for use as a servo amplifier. Being one of the largest tubes in its class, it can handle significantly higher plate voltages than similar tubes, up to 800 V. However, the TT21 and TT22 beam tetrode is an equivalent device with an almost identical transfer characteristic but different pinout, higher plate voltage ratings (1.25 kilovolt) and higher power output capability (200W class AB1 push pull). The now scarce TT21/22 has the anode connected to the tube's top cap.

Current production of the KT88 is limited to Shuguang (China), JJ Electronic (Slovakia), and the Russian brands manufactured by JSC Svetlana and New Sensor Corporation. NOS examples in good condition are extremely rare and quite expensive. Given its limited availability, the KT88 is rarely used in current production amplifiers, whether for guitar or hi-fi reproduction. Historically it has been far more popular with hi-fi manufacturers than guitar amplifier builders given its high-power, low-distortion characteristics.