RAISING THE TONE Heart Of Glass
in the first of a two-part feature, Jamie Dickson explores how valves influence your tone
Valves, like speakers, are one of those critically important components that nonetheless often gets overlooked when seeking to make gains in tone. If you use a solid-state amp or a digital modelling device, of course, then you don’t need to worry about these rather antiquated bottles of vacuum and voltage. But for the rest of us, a little more understanding of what makes valves tick can help you get even more from your rig – and who better to guide us through the subject than Adrian Emsley, the man who designs Orange’s formidably good-sounding combos and heads?
While small triode valves such as the ubiquitous 12AX7/ECC83 control gain, EQ and other functions in the preamp section of your amp, Adrian explains, it’s the big tubes in the power stage of the amplifier – the so-called power valves – that really define the sonic character of your amp.
To illustrate why, Adrian points to some important design differences between the British power valves, such as the EL34, KT88/66 and EL84, and the American ones, such as the 6L6 and 6V6.
“American power valves are pulled to a tighter vacuum and they are heated less,” Adrian says, referring to the necessity for all valves to be electrically heated and for a vacuum to exist inside the bottle in order for them to work. “The heaters draw less current, so the US power valves run cooler, last longer and stay clean later – but then distort much more suddenly when they do start to break up.The 6V6 is the softer-sounding of the US bunch, being the lower-powered tube. So they will have a softer, more gradual distortion. But the further up the power spectrum you go, with valves like the 6L6, the later it will stay clean and the more suddenly it will distort when it distorts. The American valves are associated more with glassy-sounding clean tones and more sudden distortion.
“With the British power valves,” Adrian continues, “the distortion starts sooner but builds much more gradually.You get many more shades to it, all the way until it goes into full saturation. The downside is that they won’t last as long: they’re pulled to a softer vacuum and they’re heated more, so the heaters draw more current across the board – getting on for double what the American equivalents draw. On the other hand, the American counterparts will make slightly less output in the same circuit. A KT88 can be pushed to higher voltages than a 6550, for example. Those are the two biggest families of power valve in terms of tonal differences.”
“With the British power valves, the distortion starts sooner but builds much more gradually. You get many more shades to it”
Adrian’s very popular designs for Orange, including the best-selling ‘Terror’ family of amps, often make use of the relatively lowpowered British EL84, which also forms the bedrock of the Vox AC30 sound.Why is that, we ask?
“Purely because they’re a very ‘high slope’ tube,” he explains. “What that means is that you get more out for the signal you put in.The American tubes tend to be much lower. So you have to give them a bigger signal to get the same output. Also, with a high-slope tube you can cathode-bias it and get it to make nearly as much power as if you’d grid-biased it,” Adrian says, referring to two common electronic methods used to govern an amp’s power valves so they run in the sweet spot of their performance envelope, producing ample power and good tone without burning out. Grid-biasing is often associated with extra clout and clarity, while cathode-biased designs are often thought to be more organic and crunchy.
“A lot of companies tend to grid-bias EL84s and hit them with too much voltage,” he argues. “And that is not the best thing for either tone or reliability. I always cathode-bias EL84s – Dick Denney did it with the Vox AC30 back in the late 1950s and that is the bestsounding way to run them. Also, you’re not going to get much extra power out of an EL84 if you grid-bias it, whereas if you grid-bias an American power valve like a 6V6 or a 6L6 you’ll get probably double the power.
“A cathode-biased amp is drawing current across most of the cycle, so it’s on all the time,” Adrian explains further. “It doesn’t really matter whether you’re cranking it or whether it’s just on and ready to play – it’s still going to be drawing a similar amount of current. When [current fluctuates] too much it starts messing with the guitar tone,” he says. “So if you can get that to move around a lot less, what you get out of the amp is closer to what you put in, tonally. It’s about messing with the audio as little as possible – and then letting it go into natural saturation when you push it. Let the device do what it’s gonna do!” he smiles.
Stay tuned for next month’s column, when Adrian explains how to spot telltale signs that a valve is coming to the end of its life, how to examine vintage valves to determine if they’re still in good nick and worth buying – and how to avoid buying poor-quality new valves.