Spatial power-combining devices for higher frequency operation and increased bandwidth applications are disclosed. The spatial power-combining device includes a center waveguide section with a plurality of amplifier assemblies. The plurality of amplifier assemblies forms an input end and an output end, and an input inner conductor is mechanically attached to the input end, and an output inner conductor is mechanically attached to the output end. A method for joining a plurality of amplifier assemblies together to provide a center waveguide with an input end including an input connector receptacle and an output end including an output connector receptacle is also disclosed.