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The Faint Object Spectrograph (FOS), one of five scientific instruments being built for the Space Telescope, has recently completed a significant milestone in its progression toward final instrument assembly, integration, and test.Seven flight Digicon phototubes have been successfully manufactured and tested and a development unit of the integrated detector assembly has successfully completed a set of difficult environmental and functional tests. This paper presents the results of these tests and details the results of the Digicon tube tests including photocathode quantum efficiency, dark count rate, uniformity, distortion, resolution, and diode array performance.