When you start to push an amplifier, the characteristics of these tubes become more apparent.
Power tubes can have a dramatic effect on your amplifier’s sound. At low volumes, the difference between one tube and another can be difficult to decipher; it’s almost not worth talking about. Once you start to push a little air, however, your amplifier will show off what it can do and the power tubes will display their individual characteristics more. Keep in mind, that by using pedals, you can make pretty much any amp sound like any other amp, so this discussion is focused on how a few of the most popular power tubes differ from each other when using the amp to get your sound, and not the pedals. The tubes that readers ask about most often are the EL84, EL34 and 6L6. Here is a rundown of how these tubes differ in sound.
This tube has a snarly sound, and is usually found in smaller wattage amplifiers. They break up quickest of the three power tubes mentioned here and have the least amount of headroom. EL84s can be brighter than the EL34 (i.e. the “Vox” sound) and have a bit less low-end. In America, these tubes are known as 6BQ5. They were first produced for radios, helping to eliminate the need for a driver tube.
Found in the most well-known UK heads, such as Marshall, HiWatt, Sound City, etc., these power tubes also have a snarly sound. While they have a bit more headroom than the EL84, they are also aggressive and break up quicker. EL34s tend to compress more than the 6L6 power tube and have a darker tone. This tube is most associated with the “British Sound,” an expression often used with regard to amplifiers. EL34 tubes were quite popular in stereo amplifiers years ago.
This is the power tube most associated with the term: “California Sound.” Often used in Fender amplifiers, they tend to be used in most American made amplifiers more so than in British amplifiers. The 6L6 has more headroom and does not break up as quickly as the EL84 or EL34. These tubes tend to put out a much brighter tone with more top-end sparkle (e.g the “Fender Chime”).
For the most part, the 6V6 is considered identical to the 6L6 in general tonal characteristics. Same “California” or “Tweed” kind of tone, and most often associated with Fender amplifiers. The main difference is that the 6V6 is a lower output tube. Consequently, they break up earlier than 6L6 tubes.
Again, it is not likely that you would feel these differences at low volumes. It is when you start to push an amplifier that the characteristics of these tubes become more apparent. And keep in mind that as much as power tubes differ, amplifiers differ as well, so the overall voice and behavior of the power tube will vary depending on how the amplifier is designed. If you want to really get a feel for how these tubes differ in sound, get your hands on an amplifier such as the Mesa Lone Star, that can use both the EL34 and 6L6 power tubes.
Mesa/Boogie Dual Rectifier 6L6 vs EL34 Tube Comparison
Valve Shootout: 6L6 vs EL34
EL84 vs 6V6 18watt amp by Dave Brons