A combustor includes an end cover, an end cap downstream from the end cover, and tubes that extend through the end cap. An outer support tube extends downstream from the end cover and connects to an upstream surface of the end cap. An inner support tube extends downstream from the end cover and connects to a downstream surface of the end cap. A first plenum surrounds the inner support tube between the end cover and the upstream surface and extends radially between the upstream and downstream surfaces. A second plenum surrounds the first plenum between the end cover and the upstream surface and extends radially between the upstream and downstream surfaces.