• Two Model 575A Amplifiers in a one-wide NIM for energy spectroscopy with multiple detectors
• For scintillation detectors, proportional counters, and semiconductor detectors
• Selectable shaping time constants (0.5, 1.5, and 3 µs)
• Gated active baseline restorer for high-count-rate applications
• Automatic baseline restorer threshold control

The ORTEC Model 855 Dual Amplifier is an economical, general- purpose dual amplifier in a one-wide NIM module. The low-input noise, selectable shaping time constants, and gain range allow operation with semiconductor detectors, proportional counters, and scintillation detectors in a variety of applications. The high performance and low cost of the Model 855 allow a wide range of uses in such fields as research, environmental monitoring, and teaching.

The Model 855 incorporates an automatic gated baseline restorer (BLR) that causes the system resolution to be nearly independent of input counting rates. The gated baseline restorer includes a discriminator that operates the sensing circuits, that normally establish the baseline reference for the multichannel analyzer. Performance of the spectrometer often depends on the precision of the setting of the BLR threshold. The Model 855 offers the convenience of an automatic threshold control that typically gives results as good as, or better than, those the most experienced operator could achieve manually.

The pulse-shaping networks in the Model 855 produce semi-Gaussian-shaped output pulses resulting in improved noise performance and reduced amplifier resolving time. The shorter resolving time permits higher counting rates than in amplifiers with classical RC pulse-shaping networks. The Model 855 provides a 10-V linear output with excellent dc stability for both unipolar and bipolar output pulses.

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