6L6 Valve Guitar Amps

6L6 valves have been used in guitar amplifiers since the '50s. Popularised by Fender, the 6L6 helped to establish what is known as the "American sound". Fender still uses 6L6s in the majority of its valve amplifiers, but brands like Mesa/Boogie, EVH and Morgan also use them extensively in their models. 

But why are 6L6 amp tubes used by these brands? They are known for their ability to remain clean at high volumes, meaning that the amps that they're installed in can be turned up very loud without encountering break up. This is why amplifiers equipped with 6L6 power tubes are sometimes referred to as "high headroom" amps. A 6L6 will clip harshly when pushed to the limit though, which some players like while others don't.

This doesn't apply to all 6L6-driven guitar amps though, as many high-gain amps are fitted with these valves. Instead, these amps will mostly produce distortion from their preamp sections, while the 6L6 power tubes ensure a huge and engulfing sound at high volumes.