Krohn-Hite 7500 User manual

Model 7500
DC to 1MHz
Wideband Power Amplifier
Operating Manual
Copyright 2004. All rights reserved. Contents of this publication may not be reproduced in any form without the written
permission of Krohn-Hite Corporation. Printed in U.S.A. 8-04
Unit 4, 15 jonathan Drive, Brockton, MA 02301-5566 U.S.A.
Tel: [phone]; Fax [phone]
email: [e-mail]; web: www.krohn-hite.com

Notes

DC to 1MHz
WIDEBAND POWER AMPLIFIER
MODEL 7500
CONTENTS
Section Page
1GENERAL DESCIPTION....................................................................................1
2OPERATION......................................................................................................9
3INCOMING ACCEPTANCE AND PERFORMANCE CHECK...............................13
ILLUSTRATIONS
Figure Page
1Model 7500 Amplifier..........................................................................................ii
2Typical Average Power Output vs Frequency Curve .............................................4
3Typical RMS Voltage Output vs Frequency Curve ................................................5
4Typical RMS Output Current vs Frequency Curve.................................................5
5Typical Distortion vs Frequency Curve.................................................................6
6Typical Frequency Response Curve ....................................................................6
7Response to Square Wave Input .........................................................................7
8Operating Controls, Connectors and Indicators.....................................................8
9AC Input Wiring Diagram ....................................................................................9
10 Output Current Limiting Curve...........................................................................12
11 Test Setup for Measuring Power Output.............................................................14
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Model 7500 Wideband Power Amplifier
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Section 1
–
General Description
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SECTION 1
GENERAL DESCIPTION
1.1 INTRODUCTION
The Krohn-Hite Model 7500, shown in Figure 1, is an all solid state, direct coupled amplifier, that
provides 75 watts of continuous power (150 watts at DC), at 125 volts RMS, from DC to 100 kHz.
Frequency response of the 7500 is flat to within 0.1db, and harmonic distortion at full power output is
less than 0.1%, from DC to 10 kHz. A front panel control selects 20 db (10) or 40 db (100) of fixed
gain, or zero to 40 db of continuously variable gain. The output of the 7500 can be offset ±200 volts,
open-circuit, by means of a front panel DC offset control. The 7500 provides selectable input coupling,
either direct (DC) or capacitive (AC).
The amplifier’s output is protected from short-circuit or other abnormal load conditions by a unique
output protection circuit, that uses a modified form of foldback current limiting. The output stage is
convection cooled by a special heat sink configuration.
An optional rack-mounting kit (part no. RK-519) is available for installing the unit in a standard 19” rack
spacing.
The amplifier is carefully inspected, aged and adjusted before shipment, and should be ready for
operation when it is unpacked. If it appears to have been damaged in shipment, make a claim with the
carrier, and notify Krohn-Hite immediately.
1.2 SPECIFICATIONS (Specifications apply after a 30 minute warm-up.)
Frequency Range
DC to 1 MHz
Output Power, Voltage & Current (Specifications apply using a 200 ohm resistive load):
Power: 75 watts, DC to 100 kHz; 40 watts at 500 kHz; 10 watts at 1 MHz.
Voltage: 125 volts RMS, DC to 100 kHz; 90 volts RMS at 500 kHz; 45 volts RMS at 1 MHz.
Current: 625 milliamperes RMS, DC to 100 kHz; 450 milliampers RMS at 500 kHz; 225
milliamperes RMS at 1 MHz.
Frequency Response
Flat to within ±0.1 db, DC to 1kHz; ±1.5 db to 500 kHz; -3 db at approximately 1 MHz.
Harmonic Distortion
At 75 watts into 200 ohms, less than 0.1% to 10 kHz, approximately 1.5% at 100 kHz.
Voltage Gain
Fixed, 20 db ±0.2 db (X10) or 40 db ±0.2 db (X100), or continuously variable, zero to 40 db.
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Model 7500 Amplifier
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Gain Stability
Less than ±0.1 db change for a 10% change in line voltage.
Dynamic Range
Greater than 85 db.
Phase Shift
Zero ±1 degree from DC to 10 kHz. Phase shift increases linearly to 100 degrees (lagging) at
1 MHz.
Square Wave Response (At 100 Vp-p into 200 ohms)
Risetime, less than 500 nsec, overshoot less than 5%. Zero droop in DC coupled mode.
Maximum Input Voltage
±20 volts peak in the VARIABLE and X100 GAIN positions; ±200 volts peak in the X10 GAIN
position.
Maximum DC Component
±200 volts (except VARIABLE GAIN position) in the AC position of the INPUT COUPLING
switch.
Input Sensitivity
1.5 volts RMS at maximum gain setting.
Input Coupling
Either direct (DC), or capacitive coupling (AC) with low frequency cutoff at approximately 1 Hz.
Input Impedance
1 megohm in parallel with 85 pf in fixed gain modes; 5,000 ohms in variable gain mode.
Output Regulation
No load to 200 ohms, less than 0.5%, DC to 10 kHz.
Output Hum and Noise (1 MHz Bandwidth)
Less than 4 millivolts RMS with input shorted; less than 10 millivolts RMS with input open and
shielded.
Output Coupling
Direct.
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Section 1 –General Description
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Output DC Level
Normally zero volts. Adjustable.
Output DC Offset ( No Load)
Variable, zero to ±200 volts. Combined AC plus DC offset limited to ±200 volts.
Output DC Level Stability (After Warm-Up)
Vs. Line (short term): Less than 1 mv for 10% line voltage change.
Vs. Time: Less than 2 mv/8 hr.
Vs. Temperature: Less than 5 mv/°C.
Internal Impedance
Less than 1 ohm, DC to 10 kHz; less than 10 ohms at 100 kHz;l less than 75 ohms at 1 MHz.
Load Impedance
Capable of driving any load within the voltage and current limitations of the amplifier.
Load Power Factor
1.0 to zero, leading or lagging.
Ambient Temperature
o°C to 45°C.
Controls
Front Panel: POWER switch, 3 position push-button GAIN selector, variable GAIN control, 3
position push button DC OFFSET selector, variable OFFSET control, screwdriver control for
DC output level.
Rear Panel: CHASSIS/FLOATING ground switch.
Front Panel Indicators
Power ON, output OVERLOAD
Terminals
Front Panel: BNC for INPUT, binding posts for OUTPUT.
Rear Panel: BNC for INPUT, binding posts for OUTPUT, AC power receptable.
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Model 7500 Amplifier
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Power Requirements
105-125 or 210-250 volts, single phase, 50-400 Hz, 85 watts quiescent, 400 watts maximum.
Fuse Protection
AC line, 5 ampere slow blow (115 V), 2.5 ampere slow blow (230 V); output stage unregulated
supplies, 1 ampere fast blow (each supply).
Dimensions and Weights
Model 7500: 16-5/8” wide, 5-1/4” high, 17” deep, 35 lbs/16 kgs net, 40 lbs/18.2 kgs shipping.
Optional Rack-Mounting Kit
Part No. RK-519: Permits installation of the 7500 into a standard 19” rack spacing.
1.3 PERFORMANCE CHARACTERISTICS
The performance characteristics of the Model 7500 are illustrated in Figures 2-7. Figure 2
represents the amplifier’s typical output power levels for different resistive loads. The
maximum power output of 75 watts is obtained with a 200 ohm load. Figures 3 and 4
represent the amplifier’s RMS voltage and current output, under similar load conditions. The
amplifier’s maximum output voltage is approximately 140 volts RMS, open-circuit. The
maximum output current is obtained with a 100 ohm load. Figure 5 shows the typical distortion
of the 7500 at full power (75 watts) output. Distortion in the 7500 is less than 0.1% over most
of its range. Figure 6 represents the frequency response of the 7500 for both open-circuit and
full power output conditions. The frequency response of the 7500 to a square wave input is
shown in Figure 7 (b); the input of the 7500 is shown in Figure 7 (a). Note that the amplifier
produces very little ringing or overshoot on the signal, and that there is little, if any, rounding of
the square wave’s corners.
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Section 1
–
General Description
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Figure 2. Typical Average Power Output vs. Frequency, for Different Resistive Loads.
Figure 3. Typical RMS Voltage Output vs. Frequency for Different Resistive Loads.
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M
odel 7500 Amplifier
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Figure 4. Typical RMS Output Current vs. Frequency, for Different Resistive Loads.
Figure 5. Typical Distortion vs. Frequency at Full Power Output.
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