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What are power amp tubes used for?
What are the major differences between EL34, EL84, and 6L6 tubes?
Can I change one power amp tube for another?
In my previous article “12AX7 vs 12AT7 vs 12AU7 Tube Shootout” I explored some of the differences you can find in various tubes used in the preamp section of guitar amps and other audio gear. However, guitar amps typically feature two different tube-powered amplifier sections: the aforementioned preamp, and the power amp.
The power amp section of your guitar amp is what actually drives volume into a speaker, which requires a significantly higher amount of amplification power than the tubes used in the preamp.
As such, guitar amps have a wide variety of even more tubes that are used to power the amp, each with their own unique tone-shaping characteristics. We’ll dive into the differences between three of the most commonly used tubes found in power amps: EL34, EL84, and 6L6 tubes.
EL34 vs EL84 vs 6L6: Differences Explained
Since these tubes are used to provide output volume to drive your guitar amp’s loudspeaker, it’s natural to think that different tubes would simply provide different wattages to best drive any given speaker. That is somewhat true, but in guitar amps we actually like the sound that the tube provides when it is overdriven, so the “best” isn’t so simple.
In general, EL34 and 6L6 tubes are typically used in higher wattage applications, usually amps that are over 50 watts. EL84 tubes are used for lower wattage amps, typically in the 15 to 30 watt range, but have essentially the same sonic “flavor” as EL34 tubes. 6V6 tubes are another common type that are used for lower wattage applications and are similarly scaled-down 6L6 tubes and provide a similar sound.
The EL34 tube is among one of the most used tubes in any guitar amp. They are known for their very high headroom and high output wattage, with a pair easily being able to push out around 50 watts in a typical Class AB amp configuration.
EL34 tubes are commonly found in and associated with the “classic” big stack British guitar amplifiers, such as high wattage Marshalls, Orange, and Hiwatt. When pushed, these tubes play a big part in the classic “crunch” tone associated with British amplifiers, with a beefy midrange and lots of low-end.
It is important to note that amplifier designs that employ EL34 tubes are typically large and tend to sound best when they are pushed into loud volumes, so these amps might not be the best for your studio apartment!
On the surface, an EL84 tube is essentially a “scaled-down” version of the EL34, providing lower output volume and having a lower headroom. While it is common to see them in the same types of amplifiers as an EL34, the EL84 is also commonly used in amplifiers with a Class A design, such as the Vox AC15 and AC30.
Class A amps are a simpler output design that typically provide a sweeter and warmer saturation tone in exchange for a lower overall output volume. EL84 tubes typically exhibit a “chime-y” and bright high end, as well as a similar mid-range punch as an EL34, and a warmer, but still powerful low-end sound.
Amps with EL84s are great for getting a nice tube saturation at medium volumes, so they are great for gigging and practice while still getting true power tube saturation.
This Slovakian tube has colorful lows, loose and easy-going mid body, and a brightly shining chime for the highs. In overdrive, it offers a tight and focused bite with crisp, bright and well-defined articulation.
The 6L6 tube is generally regarded as the “American” cousin to the EL34 tube. The 6L6 is a high headroom, high wattage power tube, but it has a significantly different sonic signature to the aggressive crunch tone of the EL34.
6L6 tubes are known for their clean and bright sound, without distorting nearly as much as an EL34 or EL84. They are also characteristically known for providing a deep and clean low end and a sparkling high end without a big midrange bump.
6L6 tubes are used in virtually all of the “classic” Fender amps, which are known for their clean tones, as well as in applications in modern high gain amps such as Mesa Boogie amps or the EVH 5150. If you’re looking for an amp to be warm, bright, loud, and not add to much distortion character of its own to your amp, 6L6 is probably the way to go.
Because of their lower distortion characteristics, you can find 6L6 tube amps in higher and lower wattage amps, ranging from 30 watts to 100 watts.
Common amps that use 6L6 tubes are:
Fender Twin Reverb
Mesa Boogie Dual Rectifier
Fender Hot Rod series
Major Guitar Amp Design Styles
While I briefly mentioned some of the various amp designs that different power tubes provide, understanding the overall characteristics of different guitar amp “archetypes” can also make it easier to understand the differences between tube types.
Big British rock amps typically use EL34 tubes, and are known for their bold and aggressive rock sounds and higher gain. Amps known for their “chimey” and saturated sound, like Vox amps, typically use EL84 tubes, which can provide a medium amount of gain but in a very sweet and saturated character.
American clean amps like Fenders commonly use 6L6 tubes, as well as lots of high-wattage, high gain amps such as Mesa/Boogie amps.
Are EL84 and EL34 tubes interchangeable?
As a general rule of thumb, power amp tubes are never interchangeable for a multitude of reasons, but one of the biggest is safety. The power sections of guitar amplifiers are designed to drive a speaker (which is a significant amount of voltage) in conjunction with whatever selection of tubes the manufacturer has decided for the circuit design.
Using a different tube can result in the amplifier or speaker getting the wrong amount of voltage, which can cause the speaker to burn up, the amplifier to blow up, or both!
It’s also typically unsafe to simply swap the power amp tubes in any amp without knowing what you are doing. This is because there are other components in an amplifier that can still carry some electrical charge for quite a while after you’ve disconnected it from the power. If you accidentally touch one of these components while trying to swap a tube you can receive a fatal shock.
It’s always best to have a professional amplifier tech switch out your tubes if you do not understand the design or location of your amp’s tubes. In the specific case of swapping an EL34 for an EL84, you actually can’t swap them because the two different tubes have a different number of pins on their sockets. If you have an amplifier that runs EL34 tubes and you want to use EL84 tubes in it, you’d have to actually modify the amplifier’s power circuit and the mounting sockets to accommodate the EL84 tube.
What Is The Difference Between EL84 and EL34 Tubes?
As mentioned earlier, the EL84 and EL34 tubes are very similar in their sound, with the EL84 sometimes being referred to as a “scaled-down” EL34 tube.
When it comes to EL84 vs EL34 tubes, the biggest difference is in their headroom and overall output characteristics, with the EL84 being a lower wattage and headroom tube. You also commonly see smaller amplifier designs using EL84 tubes, but not the other way around. This is because in order to actually get a decent sound out of EL34 tube amps you need to have a significantly higher output wattage and power.
What Tube Amps Use EL84 Tubes?
The most common tube amp that uses EL84 tubes is the Vox AC30, as well as most other amps manufactured by Vox. Their circuit design is generally regarded as the “classic” use of EL84 tubes, providing a sweet gain-y midrange sound and a medium output volume.
Generally, I really like JJ tubes for EL84s or EL34s, and Mesa/Boogie for 6L6 tubes. Electro-Harmonix/Sovtek also make really great power tubes that are somewhat more affordable and generally last for a long time.
In the same way as preamp tubes, there are only a handful of actual power amp tube manufacturers in the world today, with the same factories producing the tubes for multiple brands.
While there is some tonal variation between the various brands out there, the biggest difference between any power amp tube brand comes down to their testing and tolerances between individual tubes.
Since virtually all tube amps use either a pair or a quad set of power tubes, it’s really important to try to get matched sets of tubes. A matched tube set will be tested so that the pair of tubes is essentially identical to each other, which will allow for the best performance in your amp.
At the end of the day, it’s hard to say which brand is objectively the best, as it really depends on what type of power amp tube you are after.