The Amplex was manufactured in South Bend, Indiana around 1925. It should not be confused with another radio called the Amplex "De Exer" that was manufactured during the same time period by Amplex Instruments Labs. of New York, New York.  ThAmplex receiver consists of a standard five tube TRF circuit with most of the components mounted on the base board of the cabinet.  On the front panel, "Ensign" brand tuning dials, which are marked for 360 degrees rotation, are attached to "Ensign" brand variable condensers, both of which were manufactured by Carlton Sanders of Mishawaka, Indiana.  "Ensign" condensers were designed so that when the shaft is turned, the plates slid in or out from each other in a straight line instead of in a circular rotation, common to most variable condensers.  Other noticeable features about this set are that is uses bright red painted tube sockets that were manufactured by Cutler Hammer, and the cabinet is crafted from solid pieces of Oak wood.  Currently little is known regarding the manufacturer but judging from the overall construction of the set, the likely conclusion would be that the manufacturer wasn't much more then a garage operation.  It's unknown how many of these sets were manufactured or how many survive today but it's felt by the author that these sets are extremely rare today.