1
ORTEC MODEL 142AH PREAMPLIFIER
1. DESCRIPTION
The ORTEC 142AH Preamplifier is a charge-
An input protection circuit is built into the
sensitive unit that is designed for use with room-
preamplifier circuits to protect the input FET from
temperature-operated silicon
surface-barrier
any large transient voltages that would otherwise
detectors. It has been designed to give the ultimate
damage the transistor. This is discussed in the
in both energy and timing resolution, with no
Notice on page vi. The protection circuit also
compromise through either output circuit. The
provides a damping resistance on the input so that
142AH Preamplifier is compatible with detectors
relatively long cable lengths can be used between
that have a capacitance in the range from 0 to 100
the detector and preamplifier without disrupting the
pF. It can operate with higher capacitances that
system stability.
are slightly degraded. The 142AH has a low-noise
intercept and a moderate slope.
An internal rise time compensation adjustment is
A differentiated timing output is directly compatible
See Section 4.5 for adjustment information.
with most timing applications. The typical ORTEC
modules that can use the timing signals from the
If it is necessary to remove the cover for any
142AH include the 436 100-MHZ Discriminator, 454
reason, observe the following instructions carefully
Timing Filter Amplifier, 473A Constant-Franction
to prevent serious injury to yourself and/or damage
Discriminator, and 574 Timing Amplifier.
to the instrument.
The energy range expected in typical applications
Observe the steps that are included in the
is from 0 to 200 MeV. Two simultaneous outputs
Notice on page vi to discharge the high
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
when not in
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.
accessible through a hole in the case of the unit.
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 and alter operating
characteristics.
See Section 4 for instructions that involve the
protection circuit.
