A Channel Electron Multiplier (CEMA) detector was launched on 24 February 1979 as part of the SOLEX Solar X-Ray Spectrometer/Spectroheliograph experiment aboard the U.S. Air Force Space Test Program P78-1 satellite. Since launch, this detector has successfully recorded X-rays in the 3–25 Å wavelength range. This report describes the comprehensive laboratory testing program of the flight and flight spare CEMA detectors. Quantum efficies, energy resolution and gain are given as a function of different incident photon wavelengths, voltage configurations, incident angles and life time exposures. Our results are compared to other published values.