A headset with an adjustable microphone boom which can be adjusted to and from a position near the mouth of a user and is mounted in a housing by a friction part being coupled to a flexible friction coupling which is configured in a plate in that co-operating plates are stamped out of the plate and are connected to the plate by means of flexible arms. The cover encloses an outwardly extending flange portion of a threaded closure body. The control system can maintain the anode source spot location relative to the output structure notwithstanding a change in one or more operating conditions of the x-ray source assembly.