Such a great thread! This is very similar to what we're wanting to build. We want to have a gate at our Maker's Faire in Tyler Tx that is a working theremin. But if we needed too, instead, we could do simple tube like in Gordon's you tube video post above. I love the tone it makes.
Unfortunately, we've never made a theremin! So glad you guys are here! If I wanted to make one like in the you tube video above ( tall & soothing tone) then do i google 'pitch only theremin schematics' or is there something more specific? I don't think it's in the budget to buy a kit. I'll be doing this from scratch.
Alternatively, a terpsetone would be really cool that people dance around instead of using just their hands. Are these more expensive to build? Or what are the pros and cons of each style? See this one in Melbourne: http://youtu.be/of_SuSc3OlM