KORG NUTEKT OD-S Analog Drive Pedal: Guitar and synth test // Building the NUTUBE kit - YouTube
Korg OD-S NuTube Overdrive
Guitar Pedal X - GPX Blog - Vox's Valvenergy NuTube Mystic Edge AC30 style and Copperhead Drive JCM800 style Overdrive / Preamps are fairly decent budget options for those genres
Review] Korg OD-S Nutube Overdrive - YouTube
Korg's DIY headphone amp and overdrive pedal go on sale in February | Engadget