The invention relates to a plastic tube sealing device comprising a clamp which has a pair of jaws that can move relative to each other for inserting and crimping a plastic tube, said jaws containing high-frequency (HF) jaw electrodes (12a, 12b), and comprising an electrical HF power supply circuit (8) including an HF generator (10) and the HF jaw electrodes. The plastic tube sealing device according to the invention further comprises an impedance control device (9) for acting towards maintaining an impedance of the HF power supply circuit constant during a respective welding operation by correspondingly controlling the variable impedance HF resonant circuit. For this purpose, the HF generator includes a variable impedance HF resonant circuit with a capacitor unit (13) and a coil unit (14), and comprising the jaw electrodes, wherein the inductance of the coil unit and/or the ohmic resistance of the HF resonant circuit is/are variably adjustable and/or wherein the capacitance of the capacitor unit is variably adjustable and the capacitor unit comprises an electrically controllable capacitance diode or at least one movable capacitance-altering capacitor electrode arranged in the clamp. A plastic tube sealing device of this type can be used, for example, for welding of blood collection tubes for blood donation bags.La présente invention concerne un dispositif de scellement de tube en plastique comprenant une pince qui comporte une paire de mâchoires qui peuvent se déplacer lune par rapport à lautre pour insérer et sertir un tube en plastique, lesdites mâchoires contenant des électrodes haute fréquence (HF) (12a, 12b) de mâchoire, et comprenant un circuit dalimentation électrique HF (8) comprenant un générateur HF (10) et les électrodes HF de mâchoire. Le dispositif de scellement de tube en plastique selon linvention comprend en outre un dispositif de commande dimpédance (9) permettant dagir en direction de la maintenance dune impédance de la constante de circuit dalime
