R&D Stories: The Korg Nutube 6P1

February 13 2019, 09:30
Sometimes it might seem as if any interest about tubes is always about looking back in time. But with consumer's interest in "tube sound" continuing to grow, there are companies looking at the future of tubes in a different way. This article provides an overview of the Korg Nutube 6P1, a new, miniature, low-power dual directly-heated triode device. It was developed by Korg (of musical instrument fame) and Noritake Itron, a manufacturer of vacuum fluorescent displays, in Japan. Although it is a true directly heated triode, it is manufactured differently than traditional vacuum tubes, which gives it some unique attributes.

As Pete Millett writes, "Electrically, the Nutube 6P1 is somewhat comparable to the battery-powered “hearing aid” tubes. It operates on very low voltages—the filament is rated at 700 mV, and plate supply voltages can be as low as 5 V... the filament consumes only 12 mW of power per triode, and the plate dissipation is rated at only 1.7 mW. The consequence of such low-power operation is that, compared to most traditional vacuum tubes, it also has low transconductance (gm)."

And detailing the physical construction of the device, he adds, "The Nutube is manufactured by Noritake Itron in Japan, using a process similar to the one used to make vacuum fluorescent displays. It is, in fact, a one-pixel vacuum fluorescent display (VFD) device. The plate is coated with a phosphor just like a VFD, and it glows a blueish-white color when plate current is flowing."

"A close look at a 6P1 triode shows a fine coated wire running across the device. This is the filament. Even though it is heated enough to emit electrons, it does not get hot enough to show a visible glow. Below the filament is a fine, open mesh — this is the grid. Below that is a metal plate with the phosphor (glowing) applied — this is the plate. Two triodes are packaged together into one glass package, which is again borrowed from VFD manufacturing. It looks a bit like an old 40-pin DIP IC package, but only has pins along one edge."

This article was originally published in audioXpress, May 2017.

Read the complete article now available online.
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