[en] In 1975 an electron current instability was observed in the Q-machine which was interpreted as an ion acoustical wave. Subsequently this interpretation had to be questioned. The present work is directed to a clarification of this issue. Measurements have been made on the parametric dependence of the saturated (non-linear) frequency and of the growth rate. An attempt is made to interpret the results. Recent theoretical investigations suggest that with an electron current flowing through the plasma a strong instability of the Buneman type occurs for which the linear growth rate is about three orders of magnitude larger than the linear frequency. Therefore the observed instability might be a fast growing oscillation rather than a slowly growing wave and the growth rate determines the temporal growth whithin the first period rather than the envelope of amplitudes over many periods. Comparison between theoretical predictions which at present concern only linear growth rates and experiments are difficult at present and would be more conclusive with the advent of a full non-linear theory. (G.Q.)