The head comprises a hollow body (21) carrying a series of capillary tubes (12) of rigid material, on to each of which is fixed a sleeve-type piezoelectric transducer (16). A resin (26) is injected into the hollow body so as to encase first portions of the transducers. A flexible printed circuit (28) is connected to another portion (26) of the transducers, the circuit having a series of pairs of conducting areas hot-soldered to two conducting terminals disposed on the outside surfaces of the transducers.The printed circuit (28) is fixed between the hollow body (21) and an intermediate block (35) which is closed by means of a sealing diaphragm (38), having a series of sleeves (40) which are a close fit on the ends of the capillary tubes remote from the nozzles. For manufacture of the head, the resin is injected by positioning the hollow body (21) in an apparatus comprising a support frame for the hollow body and a transverse member provided with a plurality of reference holes for receiving and precisely positioning the ends (13) of the capillary tubes (12) which carry the nozzles. The frame is provided with a series of seats for receiving the opposite ends of the capillary tubes. The seats are closed by a resilient strip having a series of holes which are a close fit on the portions of the transducers which are to remain free from the resin.