ORTEC 109A - Warranty; Noticev

NOTICE
This preampl ifier has been shipped to you with its pro
tection circuit connected into the circuit ("in"). The
protection circuit makes it almost impossible to destroy the
input FET under normal operating conditions and imposes
an almost negligible resolution degradation. The preamplifier
is thus immune to almost anything the operator is likely
to do in the way of causing transients either at the Detector
Input connector or at the Bias Input connector.
The protection circuit does not protect the detector, but
even if the detector breaks down as a result of overvoltage,
the preamplifier will survive the resulting large transients if
the protection circuit is "in". This, of course, is not true
if the protection circuit is "out", in which case the input
FET is very susceptible to destruction by transients at the
detector input connector.
109A TYPICAL RESOLUTION (keV FWHM)
Ext.
Cap.
(pF)
Protection "out"
(keV)
Protection "in"
(keV)
Rise Time, 10-90% (ns)
Protection "in"
Protection "out"
SI
Ge
Si
Ge
0
50
1000
2.85
3.72
30.4
2.29
2.99
24.4
2.86
4.00
39.5
2.3
3.22
31.7
15
25
250
15
25
250
Slope
0.0276
keV/pF
0.022
keV/pF
0.037
keV/pF
0.0294
keV/pF
If this slight degradation cannot be tolerated, then the
protection circuit can be removed by simply moving the
plug-in jumper from jn to out. The jumper is located on
the printed board next to Q1.
Warranty is voided without the protection circuitry unless
the fol lowing precautions are taken.
1. The detector bias circuitry must be COMPLETELY DIS
CHARGED before a detector, cable, capacitor, or other
capacitive device or low impedance is connected to the
DET. INPUT connector,shown in the Front View on page
V of this manual. (Refer to explanation below.)
2. Discharge the detector bias circuitry before making
ANY connections to the DET. INPUT connector.
To discharge the detector bias circuitry requires that a low
impedance (short circuit preferably) be connected across
the DET. BIAS connector, shown in the Rear View on page
V, for at least 20 SECONDS.
The input transistor will be destroyed if the DET. INPUT
connector is shorted, i.e., by connecting a detector, cable,
capacitor, or other capacitive device such as a voltmeter
probe, etc., while the detector bias components are charged.
A short circuit, short-term or continuous, wil l cause the
applied bias voltage (stored on C3) to be coupled via 03
directly to the input transistor, causing catastrophic break
down. If this happens, the only recourse is to replace Q1
and perhaps Q2 also, depending on the failure mode of Q1.
If a variable bias supply is used, merely turning down the
voltage control to zero and leaving it for at least 20
SECONDS will suffice, since the bias circuitry can discharge
itself through the output impedance of the bias supply.
Sometimes it is necessary to simply disconnect the bias
supply, such as when using batteries for bias. This situation
leaves no discharge path, so a path must be provided by
placing a short circuit or low impedance across the DET.
BIAS connector on the rear panel of the unit.
DO NOT SHORT the DET. INPUT on the front panel.