2 with two lateral wings 230 a 230 b arranged at the end to the core according to an advantageous feature core 200 is provided with means for maintaining connection points of wires 21 22 in their position illustrated in fig1 namely against the core and parallel to its axis these holding means generally include longitudinal notches formed on the centering side surfaces for example the section view of fig1 shows longitudinal slots 253 a 253 b formed in the centering side surfaces 213 a 213 b these notches being intended to respectively apply and maintain the connection wires 21 22 against the core 200 as shown in fig1 connection wire 22 is also maintained by longitudinal slot 252 a of side surface 212 a in order to improve the retention position of the connection wires second centering side surfaces are provided on the core 200 to retain the connection wires 21 22 in the longitudinal slots once they are introduced there as illustrated in fig1 for example the second retaining side surfaces of wire 22 are referenced 261 a 262 a other side surfaces of this type not shown in the drawings are symmetrically present to hold the wire 21 into the corresponding slots according to fig1 conductive annular rings 101 102 103 are then put in place by sliding along the axis of core 200 to get them respectively next to pods 240 to which they must be electrically connected fig1 shows a sectional view of the final disposition of the conductive ring 103 around the core 200 the core 200 equipped with all conductive rings is shown in fig1 rings 101 102 103 are then welded to intermediate pods 240 by laser welding electrical welding or any other suitable technology this can be.