Are there any low voltage vacuum tube theremins? (Or kits?)

Are there any schemas for low voltage vacuum tube theremins?

Example:

The ECC 82 needs 200 … 300 V, it works already with 50 V.

The ECC 86 needs 6.3 or 12.6 V.
(With such a vacuum tube there could be a low voltage vacuum tube theremin.).

Best regards
bernd