276L Low-Power Photomultiplier Base

ORTEC Model 276L Low Power Photomultiplier Base• For use with 10-stage PMTs that fit standard 14-pin sockets
• Built-in low-noise preamplifier and focus control
• Both preamplifier output and anode output
• Test input for system testing
• Protection circuit for internal transistors

The ORTEC Model 276L Low-Power Photomultiplier Tube Base and Preamplifier incorporates an integral low-noise preamplifier, a PMT base with a low-power voltage divider network, and a focus control for optimum performance in scintillation detector applications. The unit is ideally suited for use with Nal(TI) detectors.
  • Literature +

  • More Info +

    The Model 276L provides two outputs: the preamplifier output for energy analysis and the anode output for either timing or auxiliary energy analysis. The preamplifier is dc-coupled to simplify pole-zero cancellation in the main amplifier. A Test input accepts the output of a pulse generator to calibrate and test the preamplifier and the system. The Model 276L has a diode protection network to prevent damage to the internal transistors due to sudden application or removal of high voltage to the unit. The Model 276L is powered from any ORTEC main amplifier or preamplifier power supply.

    The Model 276L is directly compatible with many commercially available integrated Nal-PMT assemblies. Also, the Model 276L is directly compatible with 10-stage PMTs that fit standard 14-pin sockets.
  • Specifications +


    Integral Nonlinearity
    <±0.02%, 0 to +10 V.
    Temperature Instability <±0.005%/°C, 0 to 50°C.
    Output Rise Time <100 ns for test input or fast scintillator.
    Output Fall Time Time constant of 50 µs.
    Output Noise <50 µV rms with ORTEC main amplifier such as Model 672 and time constant of 1 µs.
    Conversion Gain Nominally 5 µV/eV with 2- by 2-inch Nal(TI) crystal and PMT gain of 106; the typical output for a 511-keV gamma ray will be 250 mV at a PMT gain of 105.
    Saturation Level +10 V into an open circuit; +5 V into 93-Ω load.
    Voltage Divider Resistor-divider connected to 10-stage PMT base. Total resistance 5.6 MΩ resulting in bleeder current of 200 µA with typical high voltage of 1 kV. The distribution is linear to all stages with the focus adjustment on the grid.


    Focus Single-turn locking potentiometer on panel for external adjustment of PMT grid potential.


    POS HV SHV connector, AMP 51494-2, for distribution of positive high voltage to PMT base; +2000 V maximum.
    Test BNC connector, accepts pulses from an ORTEC pulse generator for testing and calibration.
    Signal Preamplifier input is connected internally to dynode 10.
    Power Captive 4-m (12-ft) power cable terminated in Amphenol 17-20090 connector accepts preamplifier operating power; compatible with all ORTEC main amplifiers and the Model 4002P Portable Power Supply.
    PMT Socket TRW 3B14. Fits JEDEC B14-38 PMT pin base.

    BNC connector furnishes preamplifier positive output pulse to any ORTEC main shaping amplifier for linear energy analysis, Zo = 93 Ω, dc-coupled.
    Anode BNC connector furnishes negative anode output pulse for use for either timing or auxiliary energy analysis; Zo = 1 kΩ ac-coupled.

    Electrical and Mechanical
    Power Required
    For preamplifier, +24 V, 16 mA; –24 V, 16 mA; for PMT base, +2000 V maximum (use rated voltage for the tube that is installed).
    Weigth Net  0.65 kg (1.5 lb).    Shipping 1.3 kg (3.0 lb).
    Dimensions 5.6 cm (2.2 in.) diameter x 10.2 cm (4 in.) long; equipped with 4-m (12-ft) captive power cable.
  • Ordering Information +

    Model Description
    276L Low-Power Photomultiplier Base
    C-24-12 RG-62A/U 93-ohm cable with two BNC male plugs, 12-ft. length
    RG-58A/U 50-ohm cable with two SHV female plugs, 12 ft length
    50-ohm Terminator, BNC