Hi Andrew, I'm Marcus,
I looked at you're site with the interesting schematics and found the Black Top tube pre/octave up.
http://www.geocities.com/thetonegod/black_top/black_top.html
I'm seduced in building it, but it does not state what base voltage it needs, 120 or 240 AC (or, are you from the UK or USA).
It will depend on the transformer but most dual primary transformers use a pair of 120v windings. Since you use only one winding as a transformer you would use 120v.
Andrew