The HP 5061 manual describes the use of a low-frequency coil built into the beam tube to check that the basic functions of the beam tube (emitting and detecting cesium atoms) are okay. This check splits the debugging problem for a failed clock approximately in half. FTS/Datum made replacement cesium beam tubes for these clocks, as well as similar tubes for their own cesium clocks. Does anyone know whether their tubes have an equivalent LF coil? And if they do, what are the appropriate frequency and amplitude to drive the coil for the test? Cheers! --Stu