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85.40 - Thermionic, cold cathode or photo-cathode valves and tubes (for example, vacuum or vapour or gas filled valves and tubes, mercury arc rectifying valves and tubes, cathode-ray tubes, television camera tubes). - tubes Cathode-ray television picture tubes, including video monitor cathode-ray : 8540.12 8540.20 - - Monochrome - Television camera photo-cathode tubes tubes; image converters and intensifiers; other 8540.40 - Datalgraphic display tubes, monochrome; datafgraphic display tubes, colour, 8540.60 - Other cathode-ray tubes with a phosphor dot screen pitch smaller than 0.4 rnm - Microwave tubes (for example, magnetrons, klystrons, travelling wave tubes, carcinotrons), excluding grid-controlled tubes : 8540.7 1 8540.79 - - Magnetrons - - Other - Other valves and tubes : 8540.81 8540.89 - - Receiver or amplifier valves and tubes - - Other 8540.91 - - Of cathode-ray tubes 8540.99 - - Other This heading covers only those valves and tubes which, for different purposes, utilise the effect of electrons emitted from a cathode either in a vacuum or in gas. There are three types : thermionic valves and tubes, in which the cathode must be heated before the electrons are emitted; cold cathode valves and tubes; and photo-cathode valves and tubes, in which the cathode is excited by the action of light. According to the number of their electrodes they are termed diodes, triodes, tetrodes, etc. The same envelope may contain two or more systems with different h c t i o n s (compound valves). The envelopes are of lass, ceramic or metal or of combinations of these materials and may Incorporate means of coo mg (cooling fins, water circulation system, etc.). P There are many kinds of valves and tubes, some of which are designed for special p oses such as microwave tubes (e.g., magnetrons, travelling wave tubes, carcinotronsxystrons), disc-sealed (lighthouse) tubes, stabilising valves, thyratrons, ignitrons, etc. The heading includes : (1) Rectifying tubes and valves. These are designed for rectifying AC into DC. They ma be vacuum type, gas-filled or filled with vapour (e.g., mercury vapour), and in general ave two electrodes. Certain types (e.g., thyra.trons) have control gnds so that their operation can be regulated and even reversed (thus converting DC into AC). E (2) Cathode-ray tubes. (a) Television camera tubes (image pick-up tubes, e.g., image orthicons or vidicons). These are electron-beam tubes for the conversion of an optical image into a corresponding electrical signal, usually by a scanning process. (b) Image converter tubes. These are vacuum tubes in which an ima (usually of infra-red radiation) is projected on to a photoemissive surface whicrin turn produces a corresponding visible image on a lumiescent surface. (c) Image intensifier tubes. These are electronic tubes in which an image projected on to a photoemissive surface produces a ccrresponding intensified image on a luminescent surface. (d) Other cathode-ray tubes in which electrical signals are converted, directly or indirectly, e is the storage tube. In television receiver into visible images. An example of this or video monitor tubes, the electrons om the cathode(s), after being focussed, deflected, etc., fall in the form of a beam on a part of the inner wall (usually the end of the tube covered with fluorescent material, which constitutes a screen showing the picture t e viewer sees. % h Cathode-ray tubes are also used in radar, in oscilloscopes and in certain automatic data processing system terminals (display tubes). (3) Photoemissive tubes, vacuum or gas-Klled (also known as photoemissive cells). These consist of a glass or quartz tube containing two electrodes, of which the cathode is coated with a layer of photosensitive material (usually alkaline metal); under the action of the light, this la er emits electrons which es:ablish conductibility between the electrodes and are collecte on the anode. d' Photomultipliers are photosensitive vacuum tubes comprising a photoemissive cathode and an electron multiplier. (4) Other valves and tubes. These are usual1 vacuum type, and some have several electrodes. They are used for roducing h i d frequency oscillations, as amplifiers, as detectors, as scan converters (wi out the use of a photocathode), etc. & PARTS \ Sub'ect to the general provisions regarding the classification of parts see the General Exp anatory Note to Section XVI), parts of the goods of this heading are also c assified here, for example, electrodes (cathodes, grids, anodes), envelopes (of materials other than glass) for tubes, anti-implosion casin s for cathode-ray tubes, deflection coils for mounting around the necks of cathode-ray tubes or scanning purposes. I ! The heading excludes : (a) Glass face-plates and cones of envelopes for cathode-ray tubes (heading 70.11). (b) Metal tank mercury arc rectifiers (heading 85.04). (c) X-ray tubes (heading 90.22).