Explanatory notes
… 8540.91 - - Of cathode-ray tubes 8540.99 - - Other This heading covers only those valves and tubes which, for … tubes, stabilising valves, thyratrons, ignitrons, etc. The heading includes : (1) Rectifying tubes and valves . These … are vacuum tubes in which an image (usually of infra‑red radiation) is projected on to a photoemissive surface which …