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As the vacuum tube gained in popularity and use, competition arose between U.S. manufacturers and European manufacturers to produce new tube types. Out of this competition arose the EL34, the 6L6, the 6550 and the KT88.

The original KT88 was produced by GEC in 1956 also labeled as IEC/Mullard, or Genelex Gold Lion. It was the European answer to the American 6550 tubes, and was specifically designed for audio amplification. The KT88 is also one of the largest vacuum tubes in its class.

JJ-Tesla KT88

Current production of the KT88 is limited to factories in China, Slovakia, and Russia. These include JJ-Tesla, Genalex Gold Lion reissues, as well as Sovtek, Electro-Harmonix and the newly available EAT tubes. Original production, unused (NOS) KT88 tubes in good condition are increasingly rare and expensive, sometimes costing $900 or more a pair. Historically these tubes have been more popular in hi-fi stereo equipment than in guitar amplifiers, since it provides high power and low distortion. Guitar amplifier owners will regularly use them to replace 6550 tubes, particularly if they want less distortion.

The KT88 fits a standard eight-pin octal socket, has can be used in similar applications as the 6L6 and EL34, since they have the same pinout.

From the original GEC description, points about the KT88:

1. The KT88 is a beam pentode with aligned grids for maximum efficiency.

2. 50 watts output is available from a pair connected in the ultra linear circuit with auto bias and an HT line voltage not exceeding 500.

3. 100 watts output is available from a pair connected in the ultra linear circuit with fixed bias and an HT voltage not exceeding 560.

4. 25 watts output is available from a pair triode connected with auto bias and an HT line voltage not exceeding 500.

5. The mutual conductance of the KT88 is 11mA/V

6. An all-glass ring seal replaces the conventional pinch seal giving increased strength, higher rating and reduced dimensions.

7. The valve is mounted on an international octal base and has a heater rating of 6.3 volts., 1.8 amps.

If you use KT88 tubes, tell us what you think. How do you use them? Which brand do you prefer?

We look forward to hearing what you have to say.