Thursday, February 05, 2015

A Vacuum Tube on a Chip

A Nutube is a special kind of vacuum Tube. the marketing buzz-phrase has been "a vacuum tube on a chip," The idea has a lot of appeal and a lot of potential applications. The Nutube 6P1 is a full triode or half of a 12ax7, which is the most common type you'll find in a tube amp. Their goal is clear...but I'll try to stow my cynicism for the time being. More here and here.

Like the classic analog component, the Nutube is structured with an anode, grid, and filament.It's purported to generating the same rich harmonics as conventional vacuum tubes. But there are three substantial advantages to Nutube.
  • Low power Consumption – less than 2% of the power used  by conventional vacuum tube
  • Size - It's under 30% of the size of a conventional vacuum tube
  • Reliability – This model offer up to 30,000 hours of continuous operating life
I don't like quoting marketing literature but those are some bold claims.We have had sub-miniature tubes since the 40s, but those models were not designed for audio applications. they were almost exclusively for military applications. DARPA actually introduced micro-machined vacuum tubes for amplifying sub-millimeter waves in 2013. [SOURCE] So that work continues with tiny tubes. Most modern amps use MOSFET transistors . This has some upsides and downsides. Transistors still produce more distortion than tubes.  (If you define distortion as any component of the output that is not a component of the input) In a good solid-state amp this can be compensated for but not eliminated. For example a JFET (junction gate field-effect transistor) can be used to emulate some tube sound.

The project is a product of a partnership between Korg and Noritake.  But It was Noritake's background in vacuum fluorescent displays on which this design is based.  The Nutube appears to be (basically) a two-segment VFD (Vacuum Fluorescent Display .)That old tube comprised of anode, grid, and filament is very similar to a VFD composed of a monofilament cathode, grid, and anode. But because of that base design I have doubts that it provides much amplification. So it may be more for color, so to speak.