Noritake is a famous for making china-ware "Setomono" but also for VFD (Noritake Ise denshi). I've known VFD is just a device showing digit but they made a incredible device. A triode by VFD technology!!!
Most of vacuum tune requires high voltage but VFD is just around 12V. Moreover it is quite compact compared to general vacuum tube! They have already nice website and referring to data sheet ( You can ask KORG to get it on the website ), I quickly design a headphone amplifier!!
As same as general vacuum tube, Nutube has high input and output impedance. For driving headphone, some impedance converter is required and I simply added voltage follower. As a place holder, I used TL072 but in the real device I will use NJM8920 (MUSES8920), which is also very famous ( in Japan only?) good operational amplifier.
Not as same as general vacuum tube, minimum anode voltage of Nutube is just 8 V! (working up to 50 V from data sheet). As another voltage, GRID bias is needed, just around 3.3V. Anyway it is quite handy and safety compared to general vacuum tube circuit!
As same as another my recent project on hackaday.com, I have a plan to sell the full kit including this wonderful Nutube! A brief review of Nutube can be found in the following movie... Have fun!