A new thermal, supersonic cluster source for the investigation of binary metal cluster formation at thermodynamically well-defined expansion conditions is described. The source consists of two separately heatable cartridges. A first cartridge can be heated up to 1220 K and the second high temperature cartridge reaches maximal temperatures of 1800 K. A temperature difference of 1000 K between the two cartridges can be maintained for at least 3 h. Clustering occurs upon supersonic expansion from a conical nozzle. This cluster source has two main applications: (a) the generation of mixed metal clusters and (b) the investigation of pure metal clusters at various expansion conditions. The performance and applications of this source are illustrated by presenting results of the heterocluster formation of mixed sodium/gold and sodium/silver heteroexpansions. In addition, the influence of the oven parameters on the internal temperatures of the generated clusters is illustrated with the example ofNa2.©1997 American Institute of Physics.