The Theremin was the first electronic musical instrument inventend 99 years ago by Russian Physicist Leon Theremin (or "Lev Termen").
To celebrate the centennial of the Theremin next year Burkhard Kainka has transferred the Theremin-circuit with JFETs (published in Elektor-magazine in the Maqrch/April 2017 issue) to the "original" circuit with vacum tubes.
Burkhard is an expert in making tube-circuits work with low anode-voltage (only 40V) here and has bublished many books and articles in Elektor about tube-experiments.
The development story is told in a part story here (sorry, only in German):
There you can already see the final circuit and build a Theremin of your own.
The only piece of silicon in the circuit is a 3-transistor ring-oscillator to create the 40V from the 12V-DC for the heaters of the tubes. So it´s perfectly safe.
We forged the circuit in a (in our view) beautifully looking piece of hardware which is a miniature (but nevertheless fully working) model of the original version.
Because we need a minimum volume to make the handbend volume-antenna and the special cases we decided to make the project a Kickstarter-Campaign to bring it to the public: https://www.kickstarter.com/projects/kainkalabs/a-tube-theremin
A video with a bit of background info and a demo where I "play" the Tube-Theremin can be found on YouTube https://youtu.be/qo9lOXU81t4