Help! Tone won’t stop

Just bought a used ether wave theremin. When I turn it on, it’s already generating a tone. I can shut it off with the loop but only temporarily. The tone just plays by itself. Please tell me this isn’t normal. Is there a way to fix this issue? Is it a setting on the internal board? Please help! 

That's normal. The more the left hand get's away from the volume loop, the louder the sound. That's the principle of operation.

If your expectation was that the theremin would be normally quiet and get louder as your hand gets closer to the volume antenna, there is a modification outlined in the Etherwave Hotrodding manual (Google it) that reverses the sensing.  It's not a simple setting - it involves a few wiring changes to the components on the circuit board.

However if you plan to learn to play the theremin (as opposed to using it for special effects) I would recommend that you stick with the volume sensing as it is, even though it may seem awkward in the beginning.  There is a reason that almost everyone plays this way, and if your learning investment is based on the reversed method you may later wish you hadn't gone this route.

That said, you can adjust the pitch field so that there is a dead zone (called “zero beat”) where you can stand without your hand close to the volume loop and not have anything play. On an etherwave standard, you can adjust this by turning the knob labeled “pitch.” I’m not sure about other theremins. Generally, I adjust the pitch field so that zero beat occurs when my pitch hand (right hand in my case) is right next to my shoulder and then the lowest note starts as I move towards the pitch antenna. You can find further  guidance on how to do this by looking up how to tune your theremin.