The performance of prototype Vacuum Phototriodes in the first full sized Supercrystal array for the ECAL Endcaps

The performance of prototype Vacuum Phototriodes is presented from the first full sized Supercrystal array for the CMS ECAL Endcaps. The array was exposed to high energy electrons in H4 and tested in magnetic fields of up to 3 T in H2, in the CERN North area, in July and August 1999. The mean VPT electron yield, normalised to a naked crystal light yield of 8 photoelectrons into an HPMT, was found to be 25 electrons/ MeV at 3 T for devices from Research Institute Electron, 35 electrons/MeV for devices from Hamamatsu and 18/23 electrons/MeV from Electron Tubes.