Abstract: In a plant comprising a tunnel oven (2) and a plurality of carts moving around a closed circuit, each cart is equipped with a gripper (3) for gripping the stem of the television tube and with a set for forming the vacuum in the television tube; the gripper (3) is made up of a seat (13) and a gland (14A, 14B) for an O ring seal (11) to provide leaktightness around the stem. The ring seal (11) is protectively cooled by providing at least one block (331A, 431A) that conducts heat well when combined with one of the components (13 and/or 14) of the gripper (3). This block is able to transfer the heat from the gripper (3) out of the oven and give it up to a cold source such as a stream of air, through fins (331B, 431B) or the like. A protective shield (45) is also provided.