Specifically designed for audio amplification, the KT88 has similar ratings to the American 6550 which was designed for use as a servo amplifier.
The Sovtek KT88 was designed to offer the highest output power and the most reliable, linear performance available in a KT88. The unique tri-alloy plate structure of the Sovtek KT88 yields higher minimum plate current and higher transconductance while improving heat dissipation and reducing tube warm-up time. Its triple-carbonate Oxide Cathode allows the Sovtek KT88 to operate at full power for extended time periods without failure. These improved characteristics offer increased power output, higher amplification factors, and more precise tube matching with minimal drift while still maintaining tonal clarity.
KT88 is a low distortion, high power tube developed specifically for audio.
The original GEC KT88 was introduced back in 1958. Today, there is a number of quality current production KT88 tubes for audio or guitar applications.
All tubes listed below can be used in place of KT88 or 6550. KT90 is a higher-powered direct replacement of KT88, and KT120 is an even higher powered replacement.
KT88 is upwards compatible with 6550 tubes. You can use KT88 in place of 6550 in most cases.