Abstract: A tuner (10) for a reverberation chamber is provided comprising a plurality of electrically conductive surfaces (12) attached to each other in a Z-fold configuration. Each lateral edge (15) of the tuner is contacted with a generally planar, laterally positioned substrate (16) which prevents lateral extension or medial compression of the Z-fold. Optionally, end substrates (18) are attached to each of the two leading edges (17). Also, a device minimizes electromagnetic radiation leakage along a shaft including: a bearing housing; a plurality of thrust bearings contacting the bearing housing and axially juxtaposed along the shaft so that at least two thrust bearings oppose each other; a radial bearing intermediate each thrust bearing; and a provision for adjustably moving the thrust bearings toward each other so as to compress the thrust bearings against the bearing housing.