
Re: All I had was a Z80 and a handful of switches
Excuse me, but for a valve you'll need at least 3v for the filament ( at a good 100mA bare minimum ) and 15V for the Anode/Cathode to be able to work properly.
I seriously doubt that you'll get this kind of power from a single potato and 2 nails.
Obviously, with a good bag of potatos it would be another matter entirely.