The charge in the photomultiplier output pulse is integrated on the input capacitance of the preamplifier to produce a voltage pulse. A non-inverting voltage amplifier (gain ≈ 1 ) drives this pulse into the output load. Switch selection of the input capacity permits control of the sensitivity of the preamplifier. The input capacity of the Model 113 is ~45 pF plus the capacity selected by a front-panel switch (0, 100, 200, 500, or 1000 pF).
The Model 113 should be used with a shaping main amplifier, such as ORTEC Model
460,
570 Series,
671,
672, and
590A.
A diode network prevents destruction of the input transistor if a sudden positive or negative high voltage is applied to the input.