GEC KT66

MO Valve Company - Marconi Osram - Genalex
General Electric Company Ltd. of England

The GEC KT66 is one of the best tubes ever made for guitar amps. The GEC KT66 was made by the M-O Valve Company (or the Marconi-Osram Valve Company) which was a part of the General Electric Company Ltd. of England (GEC). GEC also manufactured tubes under the name of Genalex. The "KT" prefix in the KT66 stands for "Kinkless Tetrode" (aka Beamless Tetrode). This refers to the way a valve characteristic curve kinks as it progresses from Class A through Class AB towards Class B. Unfortunately, GEC closed its doors in the early 80's.

The GEC KT66 is basically the British version of the American 6L6. They were used on JTM 45's whenever the 5881 tubes weren't available. They had a 5881 supply problem, so many JTM 45's were sold with the KT66's. They were also used on the very early production Marshall 100w heads (also known as the JTM 45 100 heads). These also had the JTM 45 plexi faceplate, but with a larger head cab. Of course, these tubes were also often used in the original Marshall Bluesbreaker combo's. These tubes can also be seen with the Gold Lion logo on them. Below, you can see a pair of KT66's installed in a 1965 Block Logo Marshall JTM 45. The rectifier shown is a Mullard GZ34, and the preamp tubes are Mullard ECC83's.
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