Best KT66 Review

KT66 Tube History

British GEC/MOV developed the KT66 tube for the European audio market. KT66 tube became very popular in European radios and audio equipment.

Internally, the KT66 tube is an improved and redesigned 6L6 tube.

The KT66 tube has a shorter and fatter plate assembly and has a larger cathode than 6L6 tube. The KT66 tube is more linear and has less of the "kink" in its transfer curve compared to 6L6.

This linearity resulted in the KT66 tube producing less distortion than the 6L6.

Famous KT66 Amps

Very well known amps were designed with KT66 tube. For example, legendary LEAK Quad II and Heath W5M use KT66 tube in Williamson circuit.

And of course, the Marshall JTM45 and its derivative models 1961 and 1962 used the KT66 tubes. These Marshall KT66 tube amps are called the Bluesbreaker and known for their round bell-like tone.

KT66 tube amps were not as popular in the US, but we find KT66 amps to be a sleeper. We have yet to hear a KT66 amp that we didn't like.

KT66 vs 6L6

The KT66 tube is pin-compatible and electrically very similar to 6L6 tube. The KT66 can be used in place of 6L6, but with a caveat.

The KT66 tube draws 1.27A filament current, where 6L6 tube draws only 0.9A. This extra current shouldn't be a problem in most cases, but when in doubt, you should check the amp's filament supply rating.

Some of the current production KT66 is actually a 6L6GC in KT66-like bottle. These tubes are essentially super-sized 6L6GC. These tubes can dissipate more power than a true KT66 or even 6L6GC.

Ultimate KT66

There are several current production KT66 on the market today, but our favorite is Genalex Gold Lion KT66.

Genalex Gold Lion KT66 is beautifully constructed, with the gorgeous looks of the original GEC KT66. Gold Lion KT66 is a true KT66. It excels at the audio application, and it shines in guitar amps.

We have done side by side comparison of Genalex Gold Lion KT66 with the original GEC KT66. We found Gold Lion KT66 to hold its own.

In addition to Genalex Gold Lion KT66, we stock current production KT66 tubes in pairs and quads. Our KT66 tubes are burned-in, tested and carefully selected to make a matching set.

If you are re-tubing a KT66 amp, or considering trying KT66 in place of 6L6, we have accurately matched sets in our KT66 tube catalog page.