Disclosed is a method for the construction of helix travelling wave tubes in which the helix is supported by insulating dielectric supports, wherein the dielectric supports, in turn, are supported by support-forming elements which project from the internal wall of the vacuum-tight casing surrounding the set, towards the helix, thus reducing the radial dimensions of the dielectric supports. In most of the embodiments, these novel support-forming elements are made of metallic material. The disclosed method greatly simplifies the construction of delay lines with low dispersion for travelling wave tubes with very great bandwidth while, at the same time, increasing the precision of assembly that can be obtained. An additional advantage of the reduction of the radial dimensions of the dielectric lies in an improvement of the possibilities of thermal conduction from the helix to the casing that surrounds the set. Another advantage of this reduction is the possibility of using costly dielectric materials such as diamond or boron nitride with face-centered cubic lattice structure.