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    User name Bryon

    Log entry time 21:43:34 on February 7,1998

    Entry number 3143

    This entry is a followup to: 3142

    keyword=SOS Cerenkov LEDs

    The SOS Cerenkov detector now has LEDs mounted on the outside of each of the
    4 phototube Winston cones. At the Present time the LED's can be driven from the
    hall C counting house via old lucite Cerenkov signal cables which have been
    connected to the LED feedthroughs as:

    Phototube # Lucite Channel Patch panel #
    1 LC5- I575
    2 LC6- I576
    3 LC7- E262
    4 LC8- E263

    Note that LC7- has some problem because a fast signal is attenuated and broadened
    on this cable; there seems to be a reflection at or very near the patch panel
    feedthrough in the counting house.

    The signal cables for the LED's DO NOT have current limiting resistors; the
    LEDs can therefore generate a lot of light. The LEDs should be drive by a
    fast (~10-20 nanosecond) pulse of +2 to +5 volts and should NEVER be driven by
    a DC voltage or any voltage above 5 volts. The best device I have found to drive
    the LEDs is a BNC pulse generater, model 8010. This device has a single positive
    polarity output with adjustable peak voltage and pulse width (down to
    ~10 nanoseconds). When the peak width is 10ns the peak voltage can be adjusted
    until the phototube generates an average of 1 photoelectron per pulse. This can then
    be used to measure the single photoelectron spectrum.