[en] An evaluation of the test results on a full-size helical tube bundle model with non-uniform tube spacings but equal ascending sense of the tube spiral, is carried out in the light of recent developments. It is shown that the excitation mechanism in such a narrowly spaced helical tube bundle is jet instability associated with broad band turbulence rather than vortex shedding. The critical tube vibration was found to be the third mode, and the corresponding lift coefficient to be Csub(L) = 0.083 for an average amplification factor of Q = 200. The annular gas space between the inner and outer shells is excited to resonance up to modes with four circular nodal lines. However, the resonances are not sharp, owing to the nature of the excitation. A fluid-elastic instability arising from coupling between the elastic tube vibration and the flow path variation was detected at the upper limit of the velocity range tested. This instability seems to be restricted to the tube bundle region in which the flexible frequencies of the neigbouring tubes are not only very close to each other, but also near to a gaseous resonance of the annular space. This condition may be critical for the operation of the heat exchangers. Thus, the gas column resonance compensate the damping effect of the non-uniformity of the tube spacings, and made it no longer an efficient means of avoiding fluid-elastic instability. (Auth.)