There’s one more concession to economy. Biasing the valves is an easy task, but not as easy as the automated systems now in place in more exotic equipment. It means you need to tangle with a multimeter and probes, in the way you always had to in the good ol’ days of audio. But with this, comes a little treat, albeit one that ‘is not recommended’ (but, curiously, mentioned) in the manual. The bias voltage and current has set recommendations for the type of output tube; turning the bias current up beyond that recommendation takes the amplifier out of Class AB1 and into pure Class A. This is ‘not recommended’ because it causes the valves to run hotter and shortens their working life. However, moving to pure Class A is tempting, because the sound is sweeter (and a lot of today’s valve amp makers push their amps into Class A by default). Just remember that turning up the bias means gently pushing the tubes out of their comfort zone; it does not mean cranking the bias so high you have four incandescent lamps burning bright (and burning out) before your very eyes.
The other options open to the listener are two sets of toggle switches that switch the amp between triode-strapped and full (ultralinear) pentode mode (triode is generally sweeter, but not as powerful) and a cut in global feedback (sort of ditto; lower feedback sounds a little more direct). As with all these concepts, the best answer is ‘experiment’. Try it with and without, depending on loudspeakers. Don’t expect profound changes though; it’s more subtle than that.
The one design hiccup in my opinion is the switches for adjusting feedback or changing bias are hidden behind the valve cage. As are the neat retro power meters. The cage hides all this from view, and the cage itself undermines the elegance of the overall design. I can’t suggest playing the amplifier without the cage for the same reason the manufacturer can’t recommend turning the bias up to put the amplifier in Class A. From a Euromentalist viewpoint, hiding the tubes behind a cage prevents them from escaping into the wild, burning, cutting, and electrocuting any life-forms that happen to be in the room at the time. Pragmatically, unless you have young kids, you might want to consider using the amplifier nude – the amp, not you.