[en] A low-energy test set-up for the measurement and optimisation of secondary electron currents from the collector in electron coolers is presented. A variable-field Wien filter and current-measuring aperture plates grant insight into the trajectory and energy distribution of the secondary particles. While secondary electrons flowing back from the collector can be bent away and dumped, these electrons in turn create new secondaries (“tertiaries”), and the resulting cascade is what ultimately limits the performance of the whole collector assembly, i.e. collector, optics, and Wien filter as a complete unit. Our set-up aims at understanding the behaviour of secondary and tertiary electrons inside this assembly. Using the included diagnostic devices, the efficiency of the collector itself can be measured as a function of the beam parameters and optics; some measurements of a COSY-style collector are given as an example.