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 Tubes

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The amplifier is powered by two single triode vacuum tubes per channel. The use of single triodes allows of better matching than the more common dual triode (two tubes in one glass envelope) can possibly offer. These tubes, type 5842 perhaps represent one of the finest examples of the triode and is ideally suited to its application within the K-70.

The larger tubes are type 6X5 rectifiers, one pair being used to supply the high voltage requirements of the 5842’s.

 Magnetics

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A pair of 600VA “R” core transformers, are built to deliver about one horse power to the transistor output stage while a third “R” core delivers a high (400V) supply to the vacuum tubes. The “R” cores have a strong following in Japan and are our transformer of choice.
The remaining six chokes provide reactor operation making the power supply capacitor free, tightly regulated and less demanding on the quality of the installation's AC source power.

 Output PCB

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This is the K-70’s main output board and is truly a labour of love to produce. Thin tracks have been replaced by flat, wide conductors with extra low inductance. The opposite side of the board contains an identical pattern, essentially creating a “Litz” configuration for better conduction. Each 140uM layer of copper is gold plated and traditional silk screening and solder masking is omitted for sonic reasons. As in the rest of the amplifier, our special “four nines” alloyed solder is used with every wire being polished and surgically cleaned before soldering. When this delicate hand soldering, performed on each side of the board is complete, a thorough cleaning and testing process begins.

The most sensitive signal paths are hard wired with our Japanese speciality silver wires and finally all metallic surfaces are sealed with a high performance nanno seal to enhance reliability and inhibit surface deterioration.

While the board actually contains very few parts by comparison, the whole critical assembly takes days to complete. It is built solely in the pursuit of reliability and sound quality.

The board houses the finest selection of parts many of which cost many times that of what others use. Such extreme attention to detail as seen in the whole fabrication of the K-70’s output board is made worthy by the purity of the circuitry it holds.

 Capacitors

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To isolate the high DC voltage from the tubes and the low DC voltage of the transistors, a capacitor is required. There are other ways of doing it but we would rather not go there… So the choice of part is important and we use this highly expensive copper foil part. Not only for sonics but for reliability.

 Binding posts

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The WBT binding posts make a nice connection and feel good. The rather large DC power connector – of true military tradition is at ease with the combination of high current and voltages used.
Further to the right, the brown “cans” are superb capacitors from Nipon Chemi-Con. Rated to withstand 105 degrees and huge ripple currents, we have placed them on the outside of the amplifier chassis to give them the coolest possible operating temperature. Further more, ripple currents are minuscule compared to standard applications thus ensuring this part a long and stress free life.

 Tube section

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The tube section is absolutely simple – as it should be. Of course hand wired with the same silver and attention to detail. Only the highest quality ceramic tube bases will do!
Negative feedback? Local feedback? Cathode followers? Nah! Lineararity and low output impedance come naturally to this circuitry.

 DC cable

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Fitted with sturdy military grade connectors the DC cable may be ordered to custom length. Power amplifiers with separate DC power supplies are rare and in such systems it is possible that the quality of the DC cable has notable audible effect. In the K-70, the cable carries no audio signal related components and therefore possible cable interaction issue are neatly side-stepped. The only remaining criteria being that the cable is safe with the currents and voltages to be passed through it.

 Transistors

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Each channel uses thirty two power transistors, each rated to 150W giving a total capacity of almost 10KW for the system! These devices are designed for exclusive use in linear amplifier design but are not custom to us. The total array of devices are configured to give an astonishingly low output impedance of some 0.07 ohms across the audio bandwidth – without the use of negative feedback. Actual power dissipation of each part is restricted to about 10W. This, with the generous heatsinking ensures the part's silicon “chips” is operated at a reasonable temperature with minimal thermal cycling to aid both sound quality and part longevity.

 Speaker cable

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Each phase is made out of 24 strands of 0.4mm gold plated oxygen free copper, all configured into a Litz construction. The cable its self is biased to minimize the effects of "cable sound".

 Socket

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We have adopted these beautifully Japanese made Teflon tube sockets. The tubes fit in snugly making excellent electrical contact while the Teflon not only provides perfect insulation but also helps to dampen vibration that might otherwise enter into the sensitive tubes thru their pins.