RF Concepts 9500, Alpha 9500 User Manual

RF Concepts

Alpha 9500 Linear Amplifier

User Manual

www.rfconcepts.com

Product Release 1

Document Issue 1.1

February 2010

Alpha 9500 Linear Amplifier User Manual RF Concepts

Product Release 1

Alpha 9500 Linear Amplifier User Manual

Prepared for RF Concepts by MRH/JH/LJW.
To reach technical support or obtain copies of this document, go to

www.rfconcepts.com.

Copyright © 2010 RF Concepts, LLC. All rights reserved. Specifications
subject to change without notice.

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Contents

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1 Product Description 1-1

1.2 Product Capabilities 1-2

1.3 Safety Considerations 1-2

1.4 Related Products 1-3

1.5 Assistance 1-3

2. Amplifier Components and Specifications . . . . . . . . . . . . . . . . . . . 2-1

2.1 Cathode (Input-Match) Board 2-2

2.2 Center-Partition Board 2-3

2.3 Controls and Display 2-3

2.4 Display Board 2-4

2.5 Firmware 2-5

2.6 Master-Control Board 2-5

2.7 Output-Tank Circuit 2-5

2.8 Power Connections 2-5

2.9 Power Supply 2-6

2.10 Tube and Tube Deck 2-8

2.11 Specifications 2-8

3. Preparing Your Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.1 Prepare Your Station 3-1

3.2 Limitations of Operation at 90–130 VAC 3-3

4. Setting Up the Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.1 Unpack the Amplifier and Transformer 4-1

4.2 Install the Transformer 4-3

4.3 Connect the Transformer 4-4

4.4 Connect the Cables 4-7

4.5 Set the Input Drive 4-10

4.6 Connect the Transceiver Keying Line 4-10

5. Operating the Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.1 Principles of Operation 5-1

Basic operation 5-1
Operational states 5-2
Tuning modes 5-4
Faults 5-5

5.2 Start Up the Amplifier 5-5

5.3 Tune the Amplifier 5-7

(Optional) Changing antenna settings 5-7
Autotuning 5-8
Manual tuning 5-9

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5.4 Program the Amplifier Memory 5-10

5.5 Operate the Amplifier 5-12

6. Operating the Amplifier from a PC . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.1 Set Up to Operate from a PC 6-1

6.2 Operate from the PC 6-2

Main window 6-3
Simulated front panel 6-4
Tools menu 6-4
Options menu 6-5

7. Maintaining and Upgrading the Amplifier . . . . . . . . . . . . . . . . . . . . 7-1

7.1 Clean the Chassis 7-1

7.2 Retune the Amplifier 7-2

7.3 Replace the Tube and Fuses 7-2

7.4 Upgrade Firmware 7-3

On the Primary Board 7-4
On the Secondary Boards 7-5

8. Diagnosing Faults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.1 Overview 8-1

8.2 Fault Codes and Resolutions 8-2

Fault code 1 8-2
Fault code 2 8-4
Fault code 3 8-5
Fault code 4 8-5
Fault code 5 8-6
Fault code 6 8-6
Fault code 7 8-6
Fault code 8 8-6
Fault code 9 8-7
Fault code 10 8-7
Fault code 11 8-8
Fault code 12 8-9
Fault code 13 8-9
Fault code 14 8-9
Fault code 15 8-10
Fault code 16 8-10
Fault code 17 8-10
Fault code 18 8-10
Fault code 19 8-11

Terminology Term-1
Schematics Schem-1

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List of Procedures

List of Procedures

Procedure 3-1, “Prepare your station,” page 3–1

Procedure 4-1, “Unpack the amplifier and transformer,” page 4–1
Procedure 4-2, “Install the transformer,” page 4–3
Procedure 4-3, “Connect the transformer,” page 4–4
Procedure 4-4, “Connect the cables,” page 4–7
Procedure 4-5, “Connect the transceiver keying line,” page 4–10

Procedure 5-1, “Start up the amplifier,” page 5–5
Procedure 5-2, “(Optional) Change the antenna settings,” page 5–7
Procedure 5-3, “Autotune the amplifier,” page 5–8
Procedure 5-4, “Manually tune the amplifier,” page 5–9
Procedure 5-5, “Program the amplifier memory,” page 5–11
Procedure 5-6, “Operate the amplifier,” page 5–12

Procedure 6-1, “Set up to operate from a PC,” page 6–1

Procedure 7-1, “Clean the amplifier,” page 7–1
Procedure 7-2, “Replace the tube and fuses,” page 7–3
Procedure 7-3, “Upgrade firmware on the primary board,” page 7–4
Procedure 7-4, “Upgrade firmware on the secondary boards,” page 7–7

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Introduction

1

1

1.1 Product Description 1–1

1.2 Product Capabilities 1–2

1.3 Safety Considerations 1–2

1.4 Related Products 1–3

1.5 Assistance 1–3

Congratulations on your purchase of a professional-quality Alpha 9500
linear amplifier.

1.1 Product Description

The Alpha 9500 (see Figure 1-1) is an self-contained autotune HF linear
power amplifier. It is capable of continuous operation at 1500 W peak
power output on single sideband (SSB), keyed continuous wave (CW),
slow-scan television (SSTV), radioteletype (RTTY), digital modes or
FM, with no time limit.

CAUTION

!

CAUTION! Study this manual carefully before operating your

amplifier for the first time. In particular, it is extremely important that
you thoroughly review the installation and operation sections. Failure
to do so could result in serious damage not covered under warranty.

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Figure 1-1 Alpha 9500

1.2 Product Capabilities

Product capabilities include:

1.3 Safety Considerations

Continuous RF output. The Alpha 9500 is capable of 1.5 kW

•

continuous RF output on all commonly used modes and on any
authorized amateur frequency from 1.8 to 29.7 MHz (other than the
60-meter band).

Compatibility with popular amateur transceivers and exciters. The

•

Alpha 9500 requires approximately 50-65 W peak RF drive for 1.5­kW output.

Capable of full CW break-in, QSK, and all digital modes when used

•

with any appropriate transceiver.
Built-in protective functions. The control system incorporates

•

protective functions that minimize the probability of accidental
damage to the amplifier or its power tubes. In most cases, when one
of the protective functions is tripped, the amplifier goes to standby.

USB and serial interface allow for remote operations, diagnostics,

•

and firmware upgrades.

Page 1–2 February 2010

Locate the Alpha 9500 where there is good air circulation all around

•

and on top of the cabinet. The unit may become hot during operation.

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Use proper lifting techniques and two people when moving the Alpha

•

9500. The Alpha 9500 weighs approximately 69 pounds when the
transformer is installed.

Although the Alpha 9500 meets international safety standards and

•

FCC regulations, remember that the equipment works with high
voltages that can be LETHAL!

This operating manual holds information, cautions, and warnings that you
must follow to ensure safe installation and operation. Read Chapter 1
before attempting to unpack or operate the Alpha 9500. Failure to perform
procedures properly may result in amplifier damage, fire hazard, or
electric shock.

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1

IMPORTANT

!

1.4 Related Products

Never open the amplifier case without unplugging the unit

•

from the wall outlet.
Never stick objects into holes in the case.

•

Never touch an antenna during transmission.

•

Never attempt to turn on the amplifier without the cover

•

securely in place (all attachment screws reinserted).
Never turn the amplifier back on after a hard fault without

•

waiting at least 20 seconds.
Never press the ON (AMP) button after the amplifier faults to

•

power off.
Never allow liquids to enter the amplifier through the cover

•

holes.
Never cover or obscure the exhaust holes in the cover of the

•

amp.

Other products available to enhance your use of the Alpha 9500 include:

1.5 Assistance

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Alpha 2100 full-1500 W-rated 50-ohm dummy loads

•

Alpha 4500 series SWR meters and wattmeters

•

For more information, go to www.rfconcepts.com or call 303-473-9232.

Technical assistance from RF Concepts is available from several sources.

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Alpha 9500 Linear Amplifier User Manual RF Concepts, LLC
Introduction Product Release 1

Go to our website at www.rfconcepts.com and click Support. On

•

this site you can get the following assistance:

FAQs

•

Legacy equipment information

•

Manuals

•

Repair information

•

Software downloads

•

Tech tips

•

Technical support

•

E-mail us at [e-mail].

•

Fax us at 303-473-9660.

•

Phone us at 303-473-9232.

•

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Amplifier Components and Specifications

2

2.1 Cathode (Input-Match) Board 2–2

2.2 Center-Partition Board 2–3

2.3 Controls and Display 2–3

2.4 Display Board 2–4

2.5 Firmware 2–5

2.6 Master-Control Board 2–5

2.7 Output-Tank Circuit 2–5

2.8 Power Connections 2–5

2.9 Power Supply 2–6

2.10 Tube and Tube Deck 2–8

2.11 Specifications 2–8

2

The Alpha 9500 uses a single 3CX1500 (8877) high-mu external-anode
triode ceramic tube for amplification. The main power supply is an
unregulated transformer/rectifier/capacitor power supply for the high­voltage (HV) and heater circuits. All other power supplies are regulated.

The biasing and tank circuits are similar in most respects to those of the
Alpha 9500’s predecessor, the Alpha 77. The unit has thoroughly modern
computer-controlled power supply and control circuitry. Extensive safety
measures protect the amplifier against most off-nominal conditions. It has
USB and RS-232 interfaces to aid in remote operation. All front-panel
features are accessible via these interfaces.

There are six main circuit boards in the amplifier. Communications
among these is via an I2C bus.

The amplifier front and back are shown below (see Figure 2-1 and

Figure 2-2). Amplifier components are listed alphabetically and described

below.

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Figure 2-1 Amplifier front and interior

Figure 2-2 Amplifier back

2.1 Cathode (Input-Match) Board

The cathode board, housed in the tube deck, consists of a set of Pi filters
controlled by a set of five relays that are enabled based on the band-switch
setting.

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2.2 Center-Partition Board

The center-partition board contains the RF decoupling circuit on the B+
line as well as the crowbar safety circuit. When you remove the top cover
of the Alpha 9500, the spring metal of this safety device shorts out the B+
line.

2.3 Controls and Display

The Alpha 9500 controls enable you to adjust and monitor the amplifier
as needed (see Figure 2-3).

IMPORTANT Note that the front panel has, in the upper-right corner, a 7-segment

LED display. The display contains 4 digits.

!

The buttons below the display control what kind of value is displayed:
FLT, Fwd, Ig, Ip, SWR, or Vp.

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2

Figure 2-3 Amplifier controls

BAND

1.8 3.5 7 10 14 18 21 24 28

SAVE RCL DEF 1 2 AUTO

TUNE LOAD

SEGMENT

12345

MEMORY

ANTENNA SELECT

1234

RF Power kW

0 0.1 0.3 0.6 1.0 1.5 2.5

Plate Current Amps

Plate Voltage kV

ALPHA

MICROPROCESSOR CONTROLLED HF LINEAR AMPLIFIER

SWR

Grid Current mA

1 1.5 2 3 >10

0 50 100 150

0 1.0 1.5

02314

Gain

10 30 50

9500

Fwd IpVpIg SWR FLT

DIM SND PEP DEL

OPER STBY ON/OFFON

ANT SELAMP

Table 2-1 Amplifier Buttons (listed alphabetically)

Button Purpose

ANTENNA SELECT Determines which one or two of the four antenna output ports to use.
BAND Selects an amateur band, designated in megahertz (MHz).
DEL Displays the delivered power from the amplifier to the selected antenna

port in watts (W).

DIM Controls the brightness of the display LEDs.

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Table 2-1 Amplifier Buttons (listed alphabetically) (Continued)

Button Purpose

FLT Sets the 7-segment display to show the last fault. Also loads new

firmware.

Fwd Sets the 7-segment display to show forward power in W.
GAIN Displays the gain in decibels (dB).
GRID CURRENT Displays the grid current in milliamperes (mA).
Ig Sets the 7-segment display to show grid current in mA.
Ip Sets the 7-segment display to show plate current in mA.
LOAD Controls the load capacitor.
MEMORY Selects one of three sets of segment memories:

DEF — factory-default settings

•

1, 2 — User 1 and User 2 memories

•

AUTO — autotune

•

ON (AMP) Turns the amplifier tube and voltage on.
ON/OFF (ANT SEL) Turns antenna select on; the amplifier tube is not on.
OPER Sets the amplifier to the operate position.
PEP Toggles between peak power (PEP) and average power.
PLATE CURRENT meter Displays the plate current in milliamperes (mA).
PLATE VOLTAGE meter Displays the plate voltage in volts (V).
RCL (Currently nonfunctional)
RF POWER kW meter Displays the forward power in W.
SAVE Saves the current settings.
SEGMENT Selects different frequencies within each band.
SND Controls the sound volume (not yet implemented).
STBY Sets the amplifier to standby (bypass).
SWR meter Sets the 7-segment display to show SWR.
TUNE (UP or DOWN) Controls the tune capacitor.
Vp Sets the 7-segment display to show plate voltage in V.

2.4 Display Board

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The display board is the largest board in the amplifier and spans the entire
inside front panel. It has three microcontrollers, one each to control the
stepper motors; the LEDs and 7-segment display and push buttons; and
the sound controller.

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2.5 Firmware

The Alpha 9500 firmware controls and implements most amplifier
features and functions.

You can upgrade the master firmware via a serial or USB connection to a
Microsoft Windows PC. For information, see

and Upgrading the Amplifier.”

Chapter 7, “Maintaining

2.6 Master-Control Board

The master-control board monitors all critical voltages and currents in the
amplifier, as well as the input power and output forward and reflected
power. It uses these converted values to control the amplifier’s operation
and to send data to the front panel, so that the correct LEDs are lit and the
stepper motors move to the correct positions. A standard 9-pin RS-232
serial port is provided for control and monitoring and is found on the back
of the Alpha 9500. A USB port is also provided. Either port may be used,
but only one may be active at any one time.

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2

2.7 Output-Tank Circuit

2.8 Power Connections

The amplifier automatically senses when a PC is attached to the USB port,
and uses that port. If nothing is connected to the USB, the amplifier
automatically switches back to the RS-232 serial port.

The output-tank circuit provides reliable high-efficiency, low-distortion
performance in a very compact volume. The basic topology is “pi-L”,
which provides harmonic attenuation adequate to meet the requirements
of all countries globally that permit power outputs of 1500 W.

Band switching is under automatic control, accomplished by a 4-wafer
band switch. These wafers are used as multifunction tap selectors, which
simultaneously select band taps on the inductors and include varying
amounts of capacitance to provide band spread on the tune and load
capacitors. The wafers are in the RF tank area. The band-switch position
is controlled by a stepper motor in the front subchassis.

When the Alpha 9500 is powered up, it measures the line voltage and
chooses, then sets the appropriate tap setting for the transformer primary.
After it is powered up, it does not reset the tap. The amplifier can be set

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to override autotaps election and use any primary tap; it may be useful to
do so if your line voltage is unsteady or on the edge of a tap setting. For
more information, contact RF Concepts technical support.

Figure 2-4 Primary connections

2.9 Power Supply

The power supply has two major sections: a switch-mode supply for the
logic circuitry and a conventional transformer supply for all other
voltages.

When the amplifier is plugged into the AC line, the switch-mode supply
is always on and all the microprocessors are active. It is usual for some of
the front panel LEDs to blink momentarily when the unit is first plugged
in.

The remaining voltages are produced by the mains and HV boards,
described below.

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Mains Board

Figure 2-5 Mains board

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2

Power-supply functions are split between the mains board and the HV
board. The mains board deals mostly with the primary side of the
transformer. The various taps for the transformer primary are routed
through this board and so is the AC line input. Relays on the mains board
connect the AC line to the appropriate taps on the transformer primary.

When the ON (AMP) button is pressed, the microprocessor on the mains
board samples the line voltage and determines which tap to select. That
voltage tap remains selected until the amplifier is turned off, and does not
change even if the line voltage fluctuates.

If you install your amplifier in a location where the line voltage is not
steady, you can force the tap selection via the serial or USB port. For
information on how to force tap selection, contact RF Concepts technical
support.

Also on the mains board is a step-start circuit. This circuit consists of a
relay and a resistor, which are time-sequenced to limit the inrush current
into the amplifier when it is first turned on.

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HV Board

The main high voltage for the amplifier is created on the HV board using
a full-wave bridge rectifier and a bank of capacitors. This power supply
has two 10-ohm resistors, one in the positive (B+) lead and one in the
negative return to the tube cathode. This combination of resistors limits
the surge current in the case of a B+ arc.

When the power-supply current exceeds about 2.5 amps, a latching relay
opens the coil circuit of the mains tap relays on the mains board, causing
the amplifier to go to the power-off state. This hard-fault circuit operates
independently of microprocessor control.

All power-supply filter capacitors on this board have bleeder resistors that
discharge the capacitors in less than 60 seconds. If you must work on this
board, confirm the discharged condition with a voltmeter, due to the
remote possibility of bleeder resistor failure.

2.10 Tube and Tube Deck

The Alpha 9500 uses a single 8877 triode tube. The tube operates well
within its published ratings. It is operated in Class AB1, with a plate
voltage of 3300 V (nominal, full output, key down) and a cathode voltage
of 9.4 V.

The tube deck is a mechanical assembly that houses the tube socket and
the cathode (or input match) printed circuit board (PCB).

A temperature sensor mounted on the cathode PCB measures the
temperature of the air immediately below the tube socket. This
temperature measurement is used by the master controller as part of the
fault-detection software.

2.11 Specifications

The Alpha 9500 linear amplifier specifications are as follows.

Table 2-2 Alpha 9500 linear amplifier specifications

Parameter Value

Frequency coverage All amateur frequencies in the range 1.8–29.7 MHz
Power output 1500 Watts minimum
3rd Order IM <–30 dBc
SWR tolerance 3:1
Drive power 65 Watts nominal
Tube 3CX1500/8877

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Table 2-2 Alpha 9500 linear amplifier specifications (Continued)

Parameter Value

Cooling Forced air
Antenna outputs 4xSO-239 connectors
Antenna selection 1 or 2 outputs per band/segment
Input SO-239 connector
Tuning/Band switching Automatic; manual override possible
Power 100, 120, 200, 220, 240V AC, 50/60 Hz
Power tap selection Automatic
Interface Serial port with full remote-control capability
Protection Protected against all common faults
Display Bar graphs as well as digital panel meter
T/R switching Vacuum relays; QSK (full break-in)
Bypass capability 1500 Watts

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Wattmeter and antenna selector active in ON1 to allow use with exciter.

HV and tube come on in ON2 for linear use.
Width 17.5 inches
Height 7.5 inches
Depth 19.75 inches
Weight 76 pounds

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Preparing Your Station

3

3.1 Prepare Your Station

3

3.1 Prepare Your Station 3–1

3.2 Limitations of Operation at 90–130 VAC 3–3

The Alpha 9500 is capable of dramatically improving the performance of

your amateur station. It is important that you observe good engineering

practices to achieve all the benefits of such a station in a safe and reliable

manner.

This chapter provides a few important operational considerations. We

recommend that you also consult a good source of general information

such as the latest Amateur Radio Relay League (ARRL) Handbook for

Radio Amateurs, especially if this is the first high-power amplifier that

you have used.

Procedure 3-1 Prepare your station

Step 1 Provide 220 VAC power.

The amplifier runs best when powered by a 200–240 VAC circuit. If you

do not have a 220 VAC outlet in your station, have a licensed electrical

contractor install one. A minimum of a 20 A capacity is required. A 20-A

breaker on your 220-V circuit is sufficient.

When you size the circuit, be sure to include the current drawn by other

equipment that may be on the same circuit.

Select a location for the outlet as close as possible to where you expect to

operate the amplifier. If you are not sure or contemplate moving the

amplifier, consider installing two outlets.

There are many styles of power plugs, some of which are country-

specific. For this reason, the amplifier is not shipped with a plug. Ask your

contractor for two or three matching plugs during installation.

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Ask the contractor to measure the voltage and record it for reference.

Alpha 9500 Linear Amplifier User Manual RF Concepts, LLC

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3

Although the amplifier can run when connected to a 110 VAC outlet, you

WILL NOT achieve full-legal-limit output in this case. Rather, you

should not expect more than 1000 W output. For more information on the

limitations of operation when connected to a 110 VAC outlet, see

3.2, “Limitations of Operation at 90–130 VAC,” page 3–3.

Note that, when the amplifier is plugged in and turned on, it is normal to

hear the capacitors and band-switch zero themselves and a slight “clunk”

as the transformer comes up to full load.

Step 2 Provide proper airflow.

It is critical that airflow around the amplifier remain unimpeded at all

times and that the top of the amplifier remain clear of any restrictions.

Maintain at least 3 inches of clearance around the amplifier to allow for

unobstructed airflow.

If you are mounting the amplifier in a console, ensure that the exhaust air

is properly and fully removed from the console. If outlet air is drawn back

into the amplifier air intake and recirculated, the amplifier gets hotter and

hotter, resulting in degraded performance or even failure. If you are

designing your own console, consider putting in additional fans and/or

ducting to deal with waste heat.

Section

Minimize the possibility of dust or other contamination getting drawn into

or falling on the amplifier. Periodically (at least annually) clean the dust

out of the amplifier, paying particular attention to the tube fins. We

recommend the use of compressed air for dust removal.

Step 3 Ready your antenna for 1500 W.

Ensure that all antennas are rated for 1500 W and that they are carefully

tuned and installed for minimum voltage SWR.

Many antennas that are suitable for general use are unsuited for operation

with a full 1500 W of power. At this power level in a 50-ohm circuit, the

RMS current is 5.5 A and the peak RF voltage is 387 V. For SWR = 2:1,

these values double to 11 A and 775 V. The actual voltage and current at

various points in or on your antenna may actually be many times these

values.

Step 4 Provide adequate RF cabling.

The importance of a well-constructed feed-line system cannot be

overstated.

Use good-quality low-loss coaxial cable of size RG/8 or larger. The Alpha

9500 is intended for a nominal 50-ohm load. With proper matching (50

ohms) between amplifier and feedline, open-wire feeders or lines of other

than 50 ohms may be used.

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Use new, clean connectors and install them according to manufacturer

recommendations. Clean the connectors after soldering them and before

mating them with the amplifier.

Install system feedlines following good engineering practice and

according to manufacture recommendations.

33

NOTE: The FCC requires users to check their installations for

compliance with published values for allowable exposure to RF fields.

This information is available in ARRL publications, FCC printed rules,

and on the web. We strongly recommend that you do this for any

installation, both fixed and at an expedition or contest site.

If you have any questions regarding engineering your amplifier into

your amateur radio station, go to www.rfconcepts.com and click

Support.

Step 5 Provide surge protection.

Induced energy from nearby electrical storms or other power transients

may damage components. Such damage is not covered under warranty. It

is therefore important to use a good lightning arrestor. However the only

lightning-proof solution available is to disconnect antenna feedlines and

AC power when the equipment is not in use.

NOTE: Whenever the amplifier is online — either off, in standby

(STBY), or in warm-up with the WAIT LED lighted — the amplifier is

bypassed and the exciter is connected directly to the antenna. The

throughput limit in all cases is 1500 W.

3.2 Limitations of Operation at 90–130 VAC

3

Electrical-power equipment draws twice as much primary current from

120 V mains as from 240-V mains. Therefore, if you operate the Alpha

9500 on typical 120 V/20 A household circuit without exceeding the 20-

A circuit rating, you limit maximum peak power output to about

600–1000 W.

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Preparing Your Station Product Release 1

3

If your line voltage is below 110 V under load, do not expect to be able

to get 1500 W output (see

Table 3-1 Amplifier behavior with nonstandard line voltages

Line voltage Expected behavior

Low: 90–110 V Power outputs above 1000 W are not expected.

Normal: 110–130 V 1500 W PEP operation (CW or SSB) may be

High: >250 V Lifetime of the tubes may be reduced. Ask your

Table 3-1).

possible if your AC line service has sufficient
current capacity (30-A circuit recommended).
However, 1500 W continuous should not be
expected.

utility company if they can reduce your line
voltage. If this is not possible, consider placing
your own step-down transformer in line between
the AC outlet and the amplifier. A transformer
with at least 4-kVA rating is required, due to the
nature of the current waveform in the primary.
Another choice for voltage control, a ferroresonant
voltage regulator, is an expensive solution, but is a
good way to stabilize primary voltage.

NOTE If you intend to operate the amplifier at ~120 V or if other equipment

draws current from the same circuit as the amplifier, the following

apply:

1. If you replace the factory-shipped 20 A/250 V fuses with 25 A/250
V “slo-blo” fuses (for line voltages of less than 100 V), be aware
that the higher current at the lower voltage significantly warms the
amplifier’s power cord. The cord (as well as fuse holders and
some internal connectors) are operating near their maximum
ratings due to the current demand at lower voltages.

2. Ensure that the AC cord is not coiled too tightly or placed where
normal air flow is restricted, causing it to overheat.

3. You must change the two lower 2A fuses on the rear panel to 5A
fuses to allow for the increased in-rush current.

Page 3–4 February 2010

DOCNUMBER 9500

Document Issue 1.1