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The ORTEC 142AH Preamplifier is a charge-

sensitive unit that is designed for use with room-

temperature-operated

detectors. It has been designed to give the ultimate

in both energy and timing resolution, with no

compromise through either output circuit. The

142AH Preamplifier is compatible with detectors

that have a capacitance in the range from 0 to 100

pF. It can operate with higher capacitances that

are slightly degraded. The 142AH has a low-noise

intercept and a moderate slope.

A differentiated timing output is directly compatible

with most timing applications. The typical ORTEC

modules that can use the timing signals from the

142AH include the 436 100-MHZ Discriminator, 454

Timing Filter Amplifier, 473A Constant-Franction

Discriminator, and 574 Timing Amplifier.

The energy range expected in typical applications

is from 0 to 200 MeV. Two simultaneous outputs

are provided; the output marked E is for energy

measurements and the output marked T is for

timing applications. Either or both outputs may be

used as desired, since their circuits are isolated

from each other. For best results, however, the T

output should be terminated in 50

use.

A bias circuit is included to accept the operating

voltage required by the surface-barrier detector.

The bias input circuit in the preamplifier includes a

100-M

load resistor, and any detector leakage

current will have to pass through this high

resistance. A voltage drop is expected across this

load resistor, proportional to the detector leakage,

and this must be added to the bias valve for the

detector when adjusting the supply level.

ORTEC MODEL 142AH PREAMPLIFIER

1. DESCRIPTION

silicon

surface-barrier

when not in

An input protection circuit is built into the

preamplifier circuits to protect the input FET from

any large transient voltages that would otherwise

damage the transistor. This is discussed in the

Notice on page vi.

provides a damping resistance on the input so that

relatively long cable lengths can be used between

the detector and preamplifier without disrupting the

system stability.

An internal rise time compensation adjustment is

accessible through a hole in the case of the unit.

See Section 4.5 for adjustment information.

If it is necessary to remove the cover for any

reason, observe the following instructions carefully

to prevent serious injury to yourself and/or damage

to the instrument.

Observe the steps that are included in the

Notice on page vi to discharge the high

voltage to prevent shock; the voltage levels

that are used are lethal and the capacitors

are very high quality and retain a charge

much longer than is normally expected.

Do not touch the high-megohm resistors, R4

and R7, with your bare fingers; the presence

of skin oil can reduce the resistance of the

component

characteristics.

See Section 4 for instructions that involve the

protection circuit.

The protection circuit also

and

alter

operating