[SOLVED!] 6L6GC Vs. KT66: Which Tube Is The Superior One?


Nowadays, it’s not uncommon to see 6L6GC and KT66 occupying top positions in reviews of amp tubes which makes 6L6GC vs. KT66 a hotly discussed topic. If you need more details on the tubes so you could determine which ones suit you most, this article could help you out. Down below is all the information you must keep in mind about 6L6GC and KT66. By reading to the end, you would be able to make a wise investment. 

An Analysis Of The Tubes 


In case you don’t know, 6L6GC is one of the variants of 6L6, a beam-power tube made by Radio Corporation of America in April 1936. Similar to 6L6, 6L6GC is a beam-power tube that makes use of the formation of a low potential space charge region between the anode and the screen grid to return anode secondary emission electrons to the anode. In use, 6L6GC offers significant performance improvements over power pentodes. 

About KT66, it’s a beam-power tube made by Marconi-Osram Valve Co. Ltd. (M-OV) of Britain in 1937. Introduced for power amplifiers that handle audio frequencies and driver for radio frequencies, KT66 works in the same manner as 6L6GC. 


In terms of the design, both of the tubes have a glass envelope. Upon close inspection, 6L6GC is a bit smaller and lighter than the KT66 but the differences are not too significant. 


Regarding differences in the sound the tubes produce, the 6L6GC has a midrange scoop in the frequency response while the KT66 does not. Also for your information, KT in KT66 is short for Kinkless Tetrode so there is no need to worry about kink in the response. With 6L6GC, the sound is clean with headroom but it also clips harshly and abruptly. In the case of KT66, the sound is similar to the 6L6GC but with a more low-end grunt and greater clarity.

Heater Current

The heater current from the two vacuum tubes is also different: 6L6GC has a smaller max heater current compared to the KT66 (0.9A to 1.27A) which allows KT66 to function hotter with less risk of failure. In times of need, KT66 could work as an alternative to 6L6GC if you rebias the amp. 

Tech Specs

Classification Beam-Power TetrodeBeam-Power Tetrode
Power Output30 Watts25 Watts
Max voltage500V500V
Heater voltage6.3V6.3V
Heater current0.9A1.27A
Net weight65g72g

Two 6L6GC Tubes Setup: Insights

In recent years, the use of two 6L6GC tubes in the guitar amp has become widely favored. The reason behind the popularity of the setup is the high power resistance of the two tubes that permit players to play with more distortion or at a high volume. Another reason that persuades players to embrace the setup is the sound: the tone made by two 6L6GC tubes is much richer and fuller than what a single tube could provide. 

There are many great options for amp tubes using two 6L6GC vacuum tubes in the market today. You can try the Orange Micro Dark Terror amp, a model that is suitable for anyone who prefers a lot of power and great sound. The Mesa Boogie Dual Rectifier Amp is also an amazing option for players who like rich and full sound. Finally, the Hughes & Kettner TubeMeister 18-amp is perfect for users who like a tube amp that can be utilized for any kind of genre. 

What Are The Best KT66s In The Market Today? 

Gold Lion KT66

Gold Lion KT66 gives an improvement in sound and it can be described as loud as even at low to moderate volumes, you can still get a big open sound. The compression of the Gold Lion KT66 is mostly focused on the high and upper mids, creating smooth, singing sustain notes. 


JJ KT66 is a rugged tube with a similar construction to the GE 6550. The JJ producer decided to differentiate their products from other KT66 makers by removing the physical resemblance to the original British tube.  The tone of the tube is balanced and centered around some thick warm mid-range tones. 

TungSol KT66

TungSol KT66 possesses solid endurance with solid lows and smooth treble responses. The mids are balanced and don’t have the extremely sounding scooped or nasal. Moreover, the built-in quality is also very good just like any other TungSol product. Unfortunately, this model has been discontinued by the manufacturer, hence, the availability of the TungSol KT66 in the market is not good. 


All things considered, 6L6GC and KT66 are very similar with a little difference in the power output, the heater current, and the design. The sounds of these two are slightly different which proves crucial once it comes to making a choice. Keep in mind that since 6L6GC and KT66 are interchangeable, you could use them to good effect after rebiasing the amp.