for now just an idea because I've got the parts in my collection (including WW2 ammo crate/box), and I've never built tube circuits before...
specs: mono, cinch line-in, magic eye for level display, 5V USB output for smartphone/mp3player charging while playing. epic volume knob.
Optional: guitar input
Important: must look "original"/weathered (fabric cable etc). I may remove the USB output from the concept because of this (or just add an old mains outlet on the box)