Power Tube Tone
Hi folks. Welcome back to the Corner. This week we’ll be discussing an important factor in tube amplifier tone. Power tubes! The tonal characteristics, breakup quality, headroom, and output capabilities all play a part in how a tube sounds which in turn plays a big part in how an amplifier sounds. We’re going to be talking about the 4 most common power tubes found in guitar amplifiers; 6L6, EL34, 6V6, and EL84. There are others out there like the KT66 or KT88 but understanding the basic four will lead to understanding some of the not so common ones.
The Power Section
We’ll start with a quick rundown (recap for some) of a tube guitar amplifier. Guitar amps can be divided into three major sections, the preamp, the power amp, and the power supply. From our earlier discussion on rectifiers, you already know that something as simple as a voltage converting tube in the power supply can have a rather noticeable effect on the tone. Same with the preamp, from our discussion of the magical V1 tube, you know that the preamp tubes can have a rather more noticeable effect on the overall tone. Now we get to the power tubes. These tubes not only amplify the signal from the preamp, they have their own distortion and tonal characteristics. In my opinion, the power tubes play the largest part in voicing an amplifier. The power tube types defined the “American” and “British” tonality as much as the span of water between the two countries.
Think of it like this, most higher gain amplifiers have a control for gain that increases the amount of distortion on the channel. This in turn is regulated by the master volume in order to give the user control over the overall volume. This allows for overdrive and distortion at low volumes. The distortion you’re hearing is from saturating one or more preamp tubes with signal (or cascading them) until they distort. This distortion will probably tend to sound a bit fuzzy (depending on the amp) or grainy and has very little dynamic response. You’ll also notice as you raise the master volume the amp will come to life and the tone will “fill out” in the frequency spectrum as well as gaining some dynamic response. This is from the power tubes.
Now let’s take a Deluxe Reverb, 22 watts of classic “American clean tone” right? But raise the volume to about 5 or 6 and you will hear distortion from the amplifier which sounds quite different from your overdrive pedal. You’ll notice more overtones, a full, rich drive tone, and dynamics that respond to touch and the volume knob on your guitar. These are the characteristics of power tube distortion. When a power tube breaks up it seems to be more of a slight compression characteristic as the tube overdrives. Keep in mind, part of the distortion in this example is generated by the preamp as well and the combination of the two is part of the magic!
The power tube is one of the final steps in the amplifier tone equation, right before the output transformer. Various types of power tubes used in the amp have a large determining factor in its overall tonality. Keep in mind, the overall tone of an amp is the sum of its parts, the power tubes play their part but the preamp and tone section, power supply, and speakers all add up to final product. The power tubes don’t do it on their own. So let’s talk power tubes shall we?
The 6L6 tube is very common in American amplifiers and some think it has defined the “California” tone. They are very common in Fender amplifiers as well as Mesa Boogie and others. Of the four tubes we are discussing the 6L6 has the highest headroom of the lot, needing to be pushed the hardest to overdrive. 6L6’s are capable of producing up to 30 watts depending on the amp design. I have seen small, single 6L6 driven amps rated at 15 watts clean (max volume and saturation was somewhere in the neighborhood of 22 watts) as well as a pair of 6L6’s putting out 60 watts (Hot Rod DeVille) so there is quite a range of power that can be had from these.
To me, the 6L6 tends to have a large bottom end that is boomy and tubby and beautiful. As the tube compresses and saturates the bottom tightens up a bit (depending on rectifier type). The top end can be best described as sparkle. The 6L6 is a fairly bright tube with chimey top end that may need a little taming. The big low end and bright top makes the 6L6 seem like it has a midrange “scoop” to it and this characteristic is most easily heard in a Fender amp such as a Twin Reverb, Vibrolux, or Blues Deluxe. This is the classic “Fender chime” that you always hear about. While it has great headroom, the 6L6 is magical when it saturates with an even compression and a very “vintage” low end sponginess. The mids and lows come together nicely with a bit of extended highs making the overdriven tone somewhat “hard” and bright.
The 6V6 came about shorter after the 6L6 in the late 1930’s. This “little brother” tube requires less input power and did not require an expensive, large power supply to run it. This coupled with the lower output power (roughly 7-12 watts) made it the perfect tube to implement in “student” model amplifiers such as the Fender Champ and Princeton.
To me the 6V6, while having a lower output than the 6L6, has some similar traits. There is the big low end and sparkling top but the lows are a bit tighter and more controllable and the highs are smoother with less of that spiky harshness. I also hear a more present midrange in the 6V6 making it seem to be a very balanced tube tonally. When clean I still hear a lot of sparkle but less of a “scoop” and when overdriven I hear a smooth distortion with a very even balance of highs, mids, and lows as well as a softer attack and smoother highs than the 6L6. While different than the 6L6, the 6V6 is also considered an “American” sound by some.
The EL34 was originated by Mullard in 1953. Up there with the 6L6 in output power (11-30 watts I believe) the most common EL34 based guitar amplifiers will have either a pair or a quad run in a push/pull circuit for a total output of 50 watts or 100 watts respectively. The EL34 is considered by some to be a mainstay of the “British big amp” tone. This is probably due to their popularity in Marshall amplifiers.
The EL34 is a different animal than the 6L6 or 6V6 tonally. To me I hear a tighter but present low end. Not as room filling or round as the 6’s but present nonetheless. In the highs I hear a smooth tone with lots of clarity but not as much sparkle. The midrange is where these tubes really impress me. Midrange content is full and rich but not overpowering. I find that it blends perfectly with a guitar’s frequencies to make a harmonically rich tone that, to me, doesn’t sound like a “hump” in the midrange as much as a well balanced tone that will cut through a mix nicely for lead work. When overdriven, I hear the EL34 compress and scream with singing sustain that I believe is partially due to the dynamic midrange content. EL34’s seem to be right at home when pushed past the threshold into distortion and are a lovely tube for high gain applications.
The EL84 is the most abused tube in the industry but also seems to be a favorite of many guitarists and amp builders. I believe the maximum plate rating of an EL84 is 300 volts for an output of 17 watts however many amplifiers will have the EL84 running above 400 volts. These tubes really like to run hot and since they are commonly run outside their specified limits, they tend to not last as long. Fortunately, in comparison with the others we’re discussing, they are the least expensive.
The EL84 is the basis of the “Leeds” tone. Vox has given the EL84 a signature tone that has a tight low end, chimey top, and extended midrange response that sizzles and screams when overdriven. Cleans are bright and springy while the distortion tends more toward the midrange “hump” with a tight low end and sizzling top. Most EL84 amps will cut through a mix like a knife. Since the trend toward low wattage guitar amps, a lot of builders have turned to the EL84 making it a commonly found tube. Check out a VOX AC30 for classic EL84 tone.
So we’ve covered the four most commonly found guitar amp power tubes. There are many more and variants of these four out there but these have formed somewhat of a basis of comparison for other power tubes. Keep in mind, the power tube does not determine the entire tone or “flavor” of the amplifier. The preamp, tone section, transformers, speakers, and everything else used to build a guitar amp (don’t you know that red Tolex sounds different than black?) all factor into the final equation but hopefully this will provide a sort of guide post if you’re thinking about a different style amplifier or just wanting to know more about the amps you already have. This is also a subjective article based on what I hear and others will hear things differently. For those of you that own an amplifier such as a THD Univalve, try all the tubes you can and see what you hear. Thanks for reading folks and we’ll see you next time, in the Corner.