The following tubes were placed into a Mesa Boogie Mark IV without EQ and played through a 12’ Celestion speaker with a PRS Guitar. Tubes were interchanged every few minutes and a ‘gut reaction’ was recorded. Here are some comparisons and other 6L6 thoughts.

Electro Harmonix 6L6 - Great frequency response especially in lower register. This 6L6 delivers a 'darker' tone perfect for high gain or heavy saturation. Another Russian contender for best 6L6!

SED SV6L6GC - The definition of power tube! Pure, warm tone that delivers the headroom and power needed for higher gain settings as well as crisp, low-volume performance. SED sets the standard with a durable 6L6 perfect for heavy use.

Sino 5881 - All the tone for less money. The Chinese Sino delivers a quality performing 5881 with excellent tone and durability. When tone matters as much as price… winner of the 'blind taste challenge'

Sovtek 6L6 WXT+ - Crisp high end definition. Great response with an 'airy glass' over the signal. Great value for great power!

Sovtek 6L6GB - Fatty tone and full range power. This tube gives open and dynamic cleans with the ability to crunch with the best of em'.

Sovtek KT66 - A 6L6 substitute for when you want to fatten up that bottom. Added dynamics to low frequencies is just one of the reasons to try the Sovtek KT66 over a 6L6. In general, the Sovtek KT66 had a more robust tone than any other 6L6 type we tried. The glass bell on the Sovteks is shorter (4 7/8" bottom of base to top) than other KT66s in order to fit where others won't. I couldn't fit the Sino in the back of the Mesa. This tube is definitely recommended.