I built this one a few years ago for a headphone system. It sounds spectacular but honestly, Im just not much of a headphone guy so this one has sat idle most of the time.
I might have 100 hours on it total. This one has the c4s upgrade as well as the impedance switch upgrade. Here is a link to when I built it.The item "Bottlehead SET Tube Integrated Amplifier S. X 2.1 Headphone Speakers" is in sale since Friday, December 13, 2019. This item is in the category "Consumer Electronics\TV, Video & Home Audio\Home Audio\Receivers & Amplifiers\Amplifiers & Preamps". The seller is "pirchera" and is located in Peoria, Arizona. This item can be shipped to United States.