Slovakian made. High power and very aggressive dynamic tone. Punchier sounding but still a sweet tone. New GT design with heavy duty components for long life. The GT6L6S Tube by Groove Tubes is Slovakian-made with high power and very aggressive dynamic tone with more highs and lows.
Groove Tubes GT-6550-R Duet Highest power pentode for use in Marshall, Hiwatt, Ampeg SVT, the GT amps and a few other higher powered amps. Also popular for HiFi amps. Excellent response, yet it's easier to push into distortion than "A" version, a little harder sounding than "C".