The circuit is specified for roughly 20W of pure Class A audio power per channel. Both of these are situated on the same chassis, as is a fully-regulated power supply.

The audio circuits are designed with purity in mind: there are only two amplification stages, the first of which is a classic 6J5GT triode transformer coupled to the KT66 power valves (a classic British design made famous by Leak, Quad, and Williamson). The use of an interstage transformer is highly unusual, even for a valve amplifier, and this particular one has been uniquely designed to give a higher bandwidth and greater fidelity than would be possible using more conventional circuits. For that matter, the output transformers are luxuriously over-specified and allow the output valves to exert an uncommon degree of control over the loudspeakers.

Layout

Above . The transformers are all covered by stainless steel screening cans which match the chassis. In this first model, the antique 1625 output valves stand out with their top caps. As the chassis has been milled from a CAD model, the fixing holes all have very precise positions and dimensions - and it was simple to do a series of ventilation holes around each power valve socket. This particular chassis is built from 1.2mm stainless steel that has subsequently been chemically polished to a mirror-bright sheen (and is, it should be added, therefore both strong and durable). It should be added that the two carrying handles to either side are not just cosmetic - they will be needed to safely move the amplifier.

Front . As minimalist as possible, the front of the amplifier only has two gold phono sockets for each channel and the on/off switches. Having the phono sockets on the front allows them to be directly connected to the grids of the driver valves, making the signal path as short as humanly possible (very often, you'll find that valve amplifiers with phono sockets on the rear of the amp have long runs of cabling from these to the driver valves). The left-hand switch turns on the heater transformer - indicated by an orange neon - and the right-hand switch then lets the high voltage transformer be turned on - indicated by a red neon.

Back. The back of the amplifier is equally simple. The power socket - a standard IEC - lies in the centre, and the loudspeaker connections are off to either side. Running clockwise from the black socket, the three red sockets allow for 4, 8, and 16 Ohm connections. The switches next to these sockets will activate the small, transformer-coupled feedback loop: activating this may give better performance with certain loudspeakers, such as electrostatics or other difficult loads.

Underneath . The audio transformers all have perspex blanking plates to protect the multitude of audio terminals. Other than the necessary power supply cable runs and the control circuitry (on the central tag board) for the regulated power supply, this layout is extremely minimalist. The only capacitors being used for filtering are the large blue-grey LCR polypropylenes, and thus heat-sensitive electrolytics have been avoided. Not, of course, that the arrays of ventilation holes over any resistor will let the temperature below the chassis rise very much.

Operation

The two phono sockets to the front should be connected to the output of your pre-amplifier. You should then connect your loudspeakers to the terminals which best match their impedance (black is ground, and clockwise from the black terminal are the red 4, 8, and 16 Ohm terminals). You may now choose whether or not to use the optional 2-stage transformer-coupled feedback loop - you will need to experiment to see whether you prefer it on or off.