Abstract: A number of electronic modules 82, 82′, 83, 83′ are mounted on a cold finger 100 disposed within a sealed housing 104, 110, the interior 210 of which is evacuated. To minimize heat transfer by conduction, gaps are provided in the dielectric substrates carrying the input and output transmission lines providing signal paths between the modules and electrical connectors on the exterior sidewalls 106, 108 of the housing. The gaps are bridged by thin conductive wires, thereby providing low electrical, but high thermal, impedance at the gaps. A number of module assemblies may be stacked on a single cold finger. To allow modules to be adjusted under actual operating conditions, a cover having a number of spring-loaded screwdrivers extending through vacuum tight seals and aligned with adjustable components of the modules, may be temporarily substituted for the enclosure lid 110. The springs urge the screwdrivers out of engagement when no adjustment is being made to minimize heat transfer.