Alpha 8410 User Manual, Latest Version 1.1 (August 2015)

Alpha 8410 User Manual, Latest Version 1.1 (August 2015)
Alpha 8410 Linear Amplifier
User Manual
RKR Designs LLC
Document Issue 1.1
August 2015
Alpha 8410 Linear Amplifier User Manual
RKR Designs LLC
Alpha 8410 Linear Amplifier User Manual
RKR Designs LLC
632 S Sunset St
Longmont CO 80501
303-473-9232
To reach technical support or obtain copies of this document, go to
www.rksdesignsllc.com.
Copyright © 2014 RKR Designs LLC. All rights reserved. Specifications
subject to change without notice.
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Product Release 1
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 1-4
2. Amplifier Components and Specifications . . . . . . . . . . . . . . . . . . . 2-1
2.1 Boards 2-3
2.2 Controls and Display 2-6
2.3 Output-Tank Circuit 2-6
2.4 Tubes and Tube Deck 2-6
2.5 Specifications 2-7
3. Preparing Your Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
3.1 Prepare Your Station 3-1
3.2 Limitations of Operation at Nonstandard Voltage 3-4
4. Setting Up the Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
4.1 Unpack the Amplifier and Transformer 4-1
4.2 Connect the Transformer 4-2
4.3 Check the Tubes and Exhaust Chimney 4-3
4.4 Connect the Voltage Tap 4-3
4.5 Connect the Cables 4-4
4.6 Set the Input-Drive Power 4-6
4.7 Connect the Transceiver Keying Line 4-7
5. Operating the Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5.1 Principles of Operation 5-1
5.2 Start Up the Amplifier 5-2
5.3 Tune the Amplifier 5-3
5.4 Operate the Amplifier 5-7
6. Maintaining the Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6.1 Clean the Amplifier Chassis 6-1
6.2 Replace Tubes and/or Fuses 6-2
6.3 Retune the Amplifier 6-3
7. Diagnosing Faults and Troubleshooting
7.1 Diagnose Faults 7-1
7.2 Troubleshoot Problems 7-4
. . . . . . . . . . . . . . . . . . . . 7-1
Terminology Term-1
Schematics Schem-1
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Contents
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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, “Connect the transformer,” page 4–2
Procedure 4-3, “Check the tubes and the exhaust chimney,” page 4–3
Procedure 4-4, “Connect the voltage tap,” page 4–4
Procedure 4-5, “Connect the cables,” page 4–4
Procedure 4-6, “Connect the transceiver keying line,” page 4–7
Procedure 5-1, “Start up the amplifier,” page 5–2
Procedure 5-2, “Tune by the recommended dip-and-load method,”
page 5–5
Procedure 5-3, “Tune by the alternate nominal-gain method,” page 5–5
Procedure 5-4, “Operate the amplifier,” page 5–7
Procedure 6-1, “Clean the amplifier chassis,” page 6–1
Procedure 6-2, “Replace tubes and/or fuses,” page 6–2
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1
1 Introduction
1.1
1.2
1.3
1.4
1.5
Product Description 1–1
Product Capabilities 1–2
Safety Considerations 1–2
Related Products 1–3
Assistance 1–4
Congratulations on your purchase of a professional-quality Alpha 8410
linear amplifier.
1.1 Product Description
The Alpha 8410 (see Figure 1-1) is a self-contained manual-tune 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.
REMEMBER
Remember
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Amplifier components as photographed for this manual may differ
from those in your amplifier, depending on your amplifier vintage.
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Introduction
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Figure 1-1 Alpha 8410
1
1.2 Product Capabilities
Product capabilities include:
• Continuous RF output. The Alpha 8410 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 8410 requires ~50-W peak RF drive for 1.5-kW 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 interface allows for remote operations, diagnostics, and
firmware upgrades.
1.3 Safety Considerations
• Locate the Alpha 8410 where there is good air circulation all around
and on top of the cabinet. The unit may become hot during operation.
• When moving the Alpha 8410, use proper lifting techniques and two
people. Never transport the amplifier with the transformer in place.
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Alpha 8410 Linear Amplifier User Manual
Introduction
FCC regulations, remember that the equipment works with high
voltages that can be LETHAL!
This operating manual contains 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 8410. Failure to perform
procedures properly may result in amplifier damage, fire hazard, or
electric shock.
IMPORTANT
!
• NEVER open the amplifier case without unplugging the unit
from the wall outlet.
• NEVER touch an antenna during transmission.
• NEVER turn on the amplifier without the cover securely in
place and all attachment screws inserted.
• NEVER turn on the amplifier without a good ground
connection on the rear-panel ground terminal.
• NEVER turn the amplifier back on after a hard fault (that is, a
fault to power off) without waiting at least 20 seconds.
• NEVER cover or obscure the exhaust holes in the amplifier
cover. Never stick objects into the holes or allow liquids to
enter through the holes.
• NEVER allow key-down plate current to exceed 1.5 A for
more than 1 or 2 seconds. If you do and a plate current trip
occurs, it automatically resets in ~4 seconds if the amplifier
is returned to receive (key-up).
• NEVER allow the red GRID LED to stay brightly illuminated
for more than 1 second.
1.4 Related Products
Other products available to enhance your use of the Alpha 8410 include:
• Alpha 2000 full 1500-W-rated 50-ohm dummy loads
• Alpha 4500 series standing-wave-ratio (SWR) meters and wattmeters
For more information, go to www.rksdesignsllc.com or call 303-4739232.
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• Although the Alpha 8410 meets international safety standards and
1
Alpha 8410 Linear Amplifier User Manual
Introduction
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11
1.5 Assistance
Technical assistance from RKR Designs is available from several
sources.
1
• Go to our website at www.rksdesignsllc.com and click Support. On
this site you can get the following assistance:
• Alpha Forum
• FAQs
• Legacy equipment information
• Manuals
• Repair information
• Software downloads
• Tech tips
• Technical support
• E-mail us by completing a support request at
www.rksdesignsllc.com.
• Fax us at 719-428-1919.
• Phone us at 303-473-9232.
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2 Amplifier Components and Specifications
2.1
2.2
2.3
2.4
2.5
REMEMBER
Remember
Boards 2–3
Controls and Display 2–6
Output-Tank Circuit 2–6
Tubes and Tube Deck 2–6
Specifications 2–7
Amplifier components as photographed for this manual may differ
from those in your amplifier, depending on your amplifier vintage.
The Alpha 8410 uses ceramic-and-metal forced-air-cooled tetrode
vacuum tubes for amplification. The main power supply is an unregulated
transformer/rectifier/capacitor power supply for the high-voltage (HV)
and heater circuits. All other power supplies are regulated.
The control circuit uses a microprocessor “in the loop” to monitor and
control amplifier operation. There are seven circuit boards in the
amplifier:
• Center-partition board
• Control board
• Display board
• HV board
• Mains board
• Transmit/receive (T/R) board
• Tube-deck board
In addition to these, the tubes, tank circuit assembly, and transformer
complete the main sections of the amplifier. These major blocks are
described below.
The amplifier includes a 5-V power supply mounted behind the front
panel. Whenever the amplifier is plugged into the mains power, this
supply is active and there is power to the microcontroller on the main
control board. This feature enables the amplifier to be turned on or off
remotely. It also enables remote monitoring and debugging via a USB
cable connected to a computer.
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The amplifier front, back, and interior are shown below (see Figure 2-1,
Figure 2-2, and Figure 2-3). Amplifier components are listed
alphabetically and described below.
Figure 2-1 Amplifier front
2
Figure 2-2 Amplifier back
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your amplifier, depending on its vintage)
22
Figure 2-3 Amplifier interior (components may differ from those in
2
2.1 Boards
The following amplifier boards are described below in alphabetical order:
• Center-partition board
• Control board
• Display board
• HV board
• Mains board
• Transmit/receive (T/R) board
• Tube-deck board
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 amplifier, the spring metal of this safety device shorts out the B+
line.
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IMPORTANT
RKR Designs LLC
Do not defeat this safety circuit. It is placed there for your protection.
!
Control Board
2
The control board is the heart of the amplifier. It is based on a PIC
microcontroller. This microcontroller has a built-in multichannel analogto-digital converter that 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 drive the display board on the front panel.
A USB port on the back of the amplifier is provided for remote
monitoring. The USB driver for the amplifier is provided on the CD that
ships with the amplifier or is available at www.rksdesignsllc.com.
Display Board
The display board uses a MAX7219 LED driver chip. It receives data
from the controller via a serial peripheral interface (SPI). It contains a
regulator to drop voltage from +12 V to +5 V for the display.
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 that goes to ground. This combination of resistors limits
the surge current in the case of a B+ arc.
The voltage across the resistor in the negative return is used to monitor
tube plate current in the control board. It is also used to generate a hardfault condition. When the power-supply current exceeds ~2.5 A, a 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.
The regulated screen supply is also located on this board.
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.
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Amplifier Components and Specifications
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.
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. When the amplifier is initially
turned on, the tap relays operate from a voltage derived from resistors
from the AC line. They hold via contacts on the trip relay on the HV
board. The regulated –12 and –124-V supplies are also located on this
board. Many of the important voltages for the amplifier are brought to test
points on this board.
The primary voltage taps are located on the top of the mains board,
between the transformer and the front panel.There is a row of five “faston” connectors (J22 through J26) and a flying jumper connector that
mates with them.
T/R Board
The transmit/receive (T/R) board contains the RF input and RF output
relays as well as the input-power detection and output directional
wattmeter. Voltages from the detector are connected to the control board.
A trimmer capacitor on this board has been adjusted at the factory with
the amplifier operating into a good 50-ohm dummy load. This capacitor
should be adjusted only at the factory.
The board also has an 800-V protection device on the RF output.
Tube-Deck Board
The tube-deck board is located in the tube deck, below the tube sockets. It
contains critical circuit elements that need to be in close proximity to the
tubes. The tube heater, bias, and screen connections are all located on this
board. The tube-deck temperature sensor and the input match for the tubes
complete this board.
For more information on the tube deck, see Section 2.4, “Tubes and Tube
Deck,” page 2–6.
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Mains Board
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2.2 Controls and Display
The Alpha 8410 controls enable you to adjust and monitor the amplifier
as needed (see Table 2-1).
2
Table 2-1 Amplifier controls
Control
Purpose
BAND
Selects an amateur band, designated in megahertz
(MHz).
LOAD
Controls the load capacitor. Sets the amplifier plate
loading and determines the power level at which best
efficiency and linearity are achieved. In general,
loading is heavier at higher output power.
TUNE
Controls the tune capacitor. Sets the output tank circuit
to resonance within each band. Higher frequencies tend
to tune toward the 0 end and lower frequencies toward
the 100 end of the dial scale.
2.3 Output-Tank Circuit
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 manual 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. A variable resistor inside
the front subchassis is used by the control board to determine which band
you have selected.
2.4 Tubes and Tube Deck
The amplifier uses two 4CX1500B (Alpha part number VTX-X120)
tetrode tubes, operating well within their ratings and in parallel.
The tubes are very rugged and normally operate with a large margin of
safety. They should provide outstanding service for many years if they are
not damaged by abuse such as overdrive or blockage of cooling airflow.
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The tubes are operated as a “swamped grid” tetrode design. The tube grids
are tied at RF to a 50-ohm swamping resistor that absorbs most of the
input-drive power. The RF voltage across this resistor is added to the
grid 1 DC bias to provide the net low-impedance tube grid 1 bias. The RF
impedance represented by grid 1 and its capacitance is compensated for
by a series inductance to provide SWR <2:1 on each band at the
amplifier’s input. At higher frequencies, a relay switches in a separate
matching network. This relay is under microprocessor control and is
actuated according to the band.
NOTE
To prolong tube life, refrain from cycling AC power on-off-on-off
repeatedly. It is less stressful to leave equipment in standby for
several hours than to cycle it on and off repeatedly.
The tube deck is a mechanical assembly enclosing the tube sockets and
the tube-deck board. The tube sockets contain the integral screen grid
(grid 2) RF bypass capacitors as well as contacts for the screen, heater,
and filament of the tubes.
2.5 Specifications
The Alpha 8410 linear amplifier specifications are as follows.
Table 2-2 Alpha 8410 linear amplifier specifications
Parameter
Value
Frequency coverage
1.8–29.7 KHz
Input-drive level
50 W nominal
Power output
1500 W
SWR tolerance
3:1
Duty cycle
100%
Tubes
2 4CX1500B (Alpha part number VTX-X120
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The tubes are operated in Class AB1, with a plate voltage of 2800 V
(nominal, full output, key down), a grid 1 voltage of –50 to –60 (minus 50
to minus 60) V, and a grid 2 voltage of 200 V. They have a lowinductance resistor in series with their cathodes. This resistor stabilizes
the tube bias and provides negative feedback, which improves linearity
and hence intermodulation distortion (IMD) performance. Electronic bias
switching (EBS) increases the negative grid 1 voltage in pauses in speech
or between Morse code elements. This reduces the standing bias on the
tubes, resulting in less waste heat, longer tube life, and higher overall
amplifier efficiency. The artifacts of EBS are not noticeable under normal
communications conditions.
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2
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Table 2-2 Alpha 8410 linear amplifier specifications (Continued)
Parameter
Value
Intermodulation level
30 dB minimum, two exciter
Harmonics
–50 dBc
Mode of operation
CW, SSB, FM
Input AC voltage
100, 120, 200, 220, 240 selectable
AC current
<15 amps @240 VAC @1500 W
Input impedance
50 ohms
Output impedance
50 ohms
RF connectors
SO-239
Cooling
Forced air
Size
17.3"W x 7"H x 21.0"D including fan space
Weight
70 lb (31.8 kg)
T/R relay
Vacuum QSK
Tuning/band switching
Manual
Display
Bar-graph LED
Interface
USB
Protection
Against all common faults
RF bypass level
<500 W
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3 Preparing Your Station
3.1 Prepare Your Station 3–1
3.2 Limitations of Operation at Nonstandard Voltage 3–4
3.1 Prepare Your Station
The Alpha 8410 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 240 VAC power.
The amplifier runs best when powered by a 200–240 VAC circuit. If you
do not have a 240 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 240-V circuit is sufficient.
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.
The amplifier is shipped with a NEMA 6-20-style plug installed.
Ask the contractor to measure the voltage and record it for reference. If
possible, have the contractor measure the line voltage with a 10-A current
draw, and use this value for setting the transformer tap.
Although the amplifier can run when connected to a 120-VAC outlet, you
MAY 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 Section
3.2, “Limitations of Operation at Nonstandard Voltage,” page 3–4.
Step 2
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Provide proper airflow.
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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 in. of clearance around the amplifier and at least 4 in.
of clearance around the air intake and exhaust areas to allow for
unobstructed airflow. Ensure that exhausted air cannot recirculate back
into the amplifier air intake. We recommend that you do not stack
equipment on top of the amplifier.
3
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.
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
at full 1500-W 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.
On a simple dipole with sharp wire ends, corona (localized ionization) can
easily occur. Corona can (and has!) led to fire in nearby objects. Traps in
beams and verticals can heat up significantly during high-power
operation. Melting or flashover of traps have occurred in many
installations where insufficient thought has been given to their ratings. If
an antenna has been deployed for a long period of time, take it down for
inspection before full-power operation. If any insulators are cracked or
show signs of tracking, replace them.
Step 4
Provide adequate RF cabling.
Use good-quality low-loss coaxial cable.
Use new, clean connectors and install them according to manufacturer
recommendations. Clean the connectors after soldering them and before
mating them with the amplifier.
Remove any excess solder from the connector; likewise, remove any
fragments of braid and the like.
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Preparing Your Station
Ensure that the connection from feed line to antenna is waterproof.
Provide for disconnection of the feed line when it is not in use. This
protects against damage caused by wind static and lightning strikes,
which are not covered under the amplifier warranty.
The importance of a well-constructed feed-line system cannot be
overstated. The purpose of the amplifier is to provide approximately 2 S
units (12+ dB) of improvement in your radiated signal. Cheap, poor, or
underrated coax and connectors can degrade performance by at least one
S unit. (This means that you could have bought a 375-W amplifier and
achieved the same radiated signal by buying good-quality feed-line
components!) Never use old coax, which may have had moisture
penetrate under the jacket.
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.rksdesignsllc.com and click
Support.
Step 5
Provide surge protection.
Induced energy from nearby electrical storms or other power transients
may damage amplifier 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, on standby
(STBY), or warming up with the WAIT LED lighted — the amplifier is
bypassed and the exciter is connected directly to the antenna. For
SWR = 1:1, the throughput limit in all cases is 500 W. For a higher
SWR, the power level should be reduced accordingly. Any power level
higher than this may damage the RF switching relays in the amplifier.
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Support the coax frequently using noncompressive clips so that it does not
hang or stretch under its own weight. Avoid sharp or kinked bends (most
manufacturers specify a minimum bend radius for their product).
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3.2 Limitations of Operation at Nonstandard Voltage
Electrical-power equipment draws twice as much primary current from
120-V mains as from 240-V mains. Therefore, if you operate the Alpha
8410 on typical 120-V/20-A household circuit without exceeding the 20A circuit rating, you limit maximum peak power output to ~600–1000 W.
3
For expected behaviors at nonstandard line voltages, see Table 3-1.
Table 3-1 Amplifier behavior with nonstandard line voltages
Line voltage
Expected behavior
Low: 90–130 V
For a line voltage of <120 V, do not expect to be
able to get 1500 W output. For maximum
efficiency, tune the amplifier for no more than
1000-W output.
For a line voltage of 110–130 V, 1500 W PEP
operation (CW or SSB) may be possible if your
AC line service has sufficient current capacity (30A circuit recommended). However, 1500 W
continuous should not be expected.
High: >250 V
NOTE
Tube lifetimes may be reduced. Ask your 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.
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. Ensure that the AC cord is not coiled too tightly or placed where
normal air flow is restricted, causing it to overheat.
2. Change the lower 2-A fuse on the rear panel to a 5-A fuse to allow
for the increased in-rush current.
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4 Setting Up the Amplifier
4.1
4.2
4.3
4.4
4.5
4.6
4.7
IMPORTANT
!
Unpack the Amplifier and Transformer 4–1
Connect the Transformer 4–2
Check the Tubes and Exhaust Chimney 4–3
Connect the Voltage Tap 4–3
Connect the Cables 4–4
Set the Input-Drive Power 4–6
Connect the Transceiver Keying Line 4–7
The Alpha 8410 is easy to set up, tune, operate, and maintain.
However, failure to carry out each procedure exactly as described in
this manual is likely to lead to amplifier damage, which is not covered
under warranty. Damage to other station equipment may also result.
Proceed slowly throughout these procedures to avoid bumping and
damaging adjacent wires, connectors, and components.
4.1 Unpack the Amplifier and Transformer
Procedure 4-1 Unpack the amplifier and transformer
Step 1
Prepare your station as described in Chapter 3, “Preparing Your Station.”
Step 2
Remove the amplifier and transformer from their cartons.
The Alpha 8410 ships in two heavy-duty double-wall cardboard boxes.
The carton containing the amplifier weighs 50 lb (23 kg); the carton
containing the transformer weighs 43 lb (20 kg).
2a Inspect the boxes for shipping damage.
2b Unpack the boxes and place the contents on a workbench or table.
2c Retain the boxes and all packing material in case you need to ship the
unit later.
Step 3
Inspect the amplifier and transformer for shipping damage.
If you find damage, call RKR Designs technical support.
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4.2 Connect the Transformer
NOTE
• The transformer is very heavy. When moving it, use due caution
and handle only by the lifting handle.
4
• Do not over-tighten the screws that hold the transformer in place,
as doing so may cause excessive vibrations or noise.
• If you move the amplifier, even if only from one site to another
locally, remove the transformer first to avoid the possibility of
damage.
Procedure 4-2 Connect the transformer
Step 1
Remove the amplifier cover and set it aside.
Step 2
Position the amplifier on a flat surface, at or near where it is to be used,
with plenty of room for you to work.
The amplifier chassis is designed for the mechanical loads experienced
when the amplifier is on a flat surface with the tilt bail up or down.
Installing the amplifier on a tilt so far that the transformer is cantilevered
or hangs out to any degree can cause the chassis to distort.
Step 3
Pick the transformer up by the handle and move it onto the lip at the edge
of the chassis, about half way into the amplifier.
Step 4
Connect the transformer:
4a Connect the transformer’s 9-pin white Molex connector to the
matching 3x3 Molex connector on the back of the amplifier’s back
wall. Use the handle to move the transformer all the way into the
amplifier and push it toward the center.
4b Connect the transformer’s 8-pin orange connector to the matching
pins on the amplifier’s mains board (the upper of the two boards).
4c Connect the transformer’s 6-pin yellow connector to the matching
pins on the amplifier’s HV board (the lower of the two boards).
4d Ensure that all connector pins on these three connectors engage fully
and correctly.
Step 5
Page 4–2
Secure the transformer into place from the bottom of the amplifier by
inserting the supplied bolts (1/4/20 ½-inch hex bolts) with ¼-inch
washers through the four clearance holes in the chassis and into the nuts
in the transformer base.
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CAUTION
CAUTION! Do not use the transformer’s shipping bolts. They are too
long and will damage the transformer!
4
4.3 Check the Tubes and Exhaust Chimney
With the amplifier cover removed, check and, if necessary, adjust the
tubes and the exhaust chimney.
Procedure 4-3 Check the tubes and the exhaust chimney
Step 1
Ensure that the tubes are firmly seated in their sockets.
The 4CX1500B tubes have bayonet-style bases. Each tube is installed
onto a central pin in the tube socket and then rotated clockwise into place
so that the flanges on the tube line up with the connectors in the socket. To
remove a tube, rotate it counter-clockwise and then pull it up out of the
socket.
Step 2
Ensure that the anode connector is tightly clamped to the tube.
Step 3
Ensure that the silicon-rubber exhaust chimney is straight and that the
bottom is firmly against the tube deck and completely covers the airflow
opening in the deck.
The chimney should be flush with the top cover when it is placed back on
the amplifier. Tube-cooling exhaust must exit only through the tube anode
fins; it must not be allowed to escape outside them.
IMPORTANT: Damage caused by insufficient cooling
airflow is not covered under warranty.
4.4 Connect the Voltage Tap
Selecting the appropriate tap for your situation optimizes amplifier
performance, safety, and lifetime.
IMPORTANT
!
We strongly recommend that you operate the amplifier on 240 VAC.
If you choose to do otherwise, see Section 3.2, “Limitations of
Operation at Nonstandard Voltage,” page 3–4.
The primary voltage taps are located on the top of the mains board,
between the transformer and the front panel.There is a row of five “faston” connectors (J22 to J26) and a flying jumper connector that mates with
them (see Figure 4-1).
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Figure 4-1 Amplifier power settings
4
Procedure 4-4 Connect the voltage tap
Step 1
Ensure that the amplifier is unplugged.
Step 2
Move the flying lead to the AC spade post marked with the appropriate
voltage.
These five nominal primary voltages — 100, 120, 200, 220, and 240 V —
cover all the line voltages normally encountered around the world. The
nominal midrange voltage for each tap is printed on the mains-board
circuit board.The acceptable line voltage for each tap is the center voltage
plus or minus 10 V. Never use a tap other than the proper voltage, or
damage to the tube and amplifier will result.
4.5 Connect the Cables
Procedure 4-5 Connect the cables
Step 1
Page 4–4
The amplifier ships from the factory with a power cord and plug. If you
ever need to change them, perform this step.
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WARNING
WARNING! To avoid the hazard of a potentially fatal electric shock
and/or severe damage to the amplifier and other equipment:
• NEVER operate the amplifier with the cover removed.
• ALWAYS use an AC plug that is appropriate for the primary mains
voltage, current rating, and configuration.
• ALWAYS use grounding-type AC connectors that conform to local
codes.
• NEVER use 120-VAC plugs to connect to power receptacles for
190–250-V circuits.
• ALWAYS connect ALL station equipment to a good common
ground. Failure to do so may allow RF feedback to leak into the
transceiver and cause severe signal distortion.
1a Connect the green wire in the amplifier power cable only to the AC
mains safety ground (or to neutral, as may be necessary with a 240-V
circuit configured 120V-N-120V without a separate ground,
commonly found in the US).
1b Connect the black-and-white power cord wires to the two hot wires
of the AC source. Either wire may be connected to either side of the
line. For best results, use a dedicated 200–240-V branch circuit of
#10 AWG copper wire or equivalent, rated at 20 A, to feed the
amplifier.
Step 2
Replace the amplifier cover and all attachment screws.
Use only the 6-32 screws supplied with the amplifier and do not tighten
any of the screws until all are started.
!
WARNING
WARNING! Do not attempt to operate the amplifier with the cover
removed or placed on the unit without the attachment screws. Doing
so damages the amplifier and may also cause injury or death to the
operator.
Step 3
Place the amplifier in its operating position on a stable surface with
sufficient space to the rear, sides, and top to allow good air flow and safe
placement of cables.
Step 4
Connect the amplifier RF INPUT to the transceiver RF OUTPUT.
Use 50-ohm coaxial cable-RG-58C/U or equivalent.
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The amplifier’s relay jack has ~12 V on it. When pulled all the way to
ground, a current of 10 mA flows. For information on how to connect to
an external amplifier, see your transceiver manual.
Step 5
4
Connect the amplifier RF OUTPUT to the antenna.
Be certain to use coax cable that is rated for at least 1500 W.
Step 6
Connect the transceiver (T/R) control cable to the amplifier’s KEY IN
input.
The amplifier has a full break-in vacuum relay QSK system that requires
only the normal interconnection when used with a modern QSK
transceiver. The amplifier requires a contact closure (short circuit) on
transmit on the amplifier’s KEY IN jack center pin to the chassis. This
function is supplied by the transceiver, usually from a dedicated relay that
is normally open in receive and closed in transmit.
6a Use shielded wire for the T/R control cable. Fit the amplifier end with
a common phono (RCA-type) plug and the transceiver end with a
suitable connector.
6b Ensure that the T/R relay contact closes. Protection circuitry prevents
hot-switching when RF drive is applied. Modern transceivers have
the proper time delay between key-up and the start of the transmitted
signal to allow the amplifier to follow the CW keying.
NOTE: The Alpha 8410’s grid-current-limiting circuits provide
substantial tube protection against possible damage. The amplifier
does not generate or use Automatic Level Control (ALC) voltages to
control an exciter. You need only set the input-drive power as
explained in Section 4.4, page 4–3.
For proper operation, set the exciter transceiver’s power output so as
not to overdrive the amplifier input. If the transceiver is more than 15
years old, reduce the power output so that voice peaks do not
overdrive the transmitter under any modulation condition.
4.6 Set the Input-Drive Power
You must set the transceiver output power properly. Virtually all damage
to date has resulted directly from severe overdrive. The amplifier requires
50-W drive for full rated output.
Damage caused by applying several-times-rated drive power to the
amplifier is not covered under warranty. Fortunately, most modern
transceivers maintain quite consistent output from band to band and mode
to mode when set up properly.
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!
CAUTION
CAUTION! It is not sufficient to set only the transceiver POWER or
RF PWR control.
Several popular transceivers can generate RF spikes of 200–300 W.
Control these spikes with a knob labeled DRIVE (IC-781, FT-1000) or
PROCESSOR OUT (TS-940,TS-950). On SSB, when you are not
using speech processing, adjust the MIC or MIKE controls. For more
information, see the manual for your particular transceiver.
4.7 Connect the Transceiver Keying Line
Procedure 4-6 Connect the transceiver keying line
Step 1
Connect the transceiver keying line.
The following is a list of popular transceivers and considerations for their
connection to the amplifier. For advice on other transceivers, contact
RKR Designs as described in Chapter 1, “Introduction.”
Table 4-1 Popular transceivers
Transceiver
Connection and keying information
Icom
RF —
T/R — Connection with the “Send” jack. For
information, see the transceiver user manual.
Kenwood
RF —
T/R — For information on connecting to external
amplifiers, see the transceiver user manual.
Yaesu
RF —
T/R — Connection with the RCA TX GND connector
and/or TX GND signal in the DIN Band Data
connector. For information, see the transceiver user
manual.
Older
transceivers
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For information on connecting to external amplifiers,
see the transceiver user manual.
Page 4–7
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Some transceivers may produce RF spikes upon keying during SSB
operations. Do not operate the amplifier with transceiver power controls
set at full power output. Do not rely on the mic gain control to set power.
Rather, set up the transceiver with proper mic gain and processor levels at
normal power level to drive the amplifier (typically 50 W).
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4
Page 4–8
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5 Operating the Amplifier
5.1
5.2
5.3
5.4
Principles of Operation 5–1
Start Up the Amplifier 5–2
Tune the Amplifier 5–3
Operate the Amplifier 5–7
5.1 Principles of Operation
Once your Alpha 8410 linear amplifier is set up as described in the
previous chapters, before first use you must tune it for peak RF output and
lowest current for the selected antenna port over the range of band
segment frequencies to be used. At that point it is ready for use.
The Alpha 8410 can be in one of seven operational states, listed in
Table 5-1
Table 5-1 Operational states
State
Off
Description
Plugged in but OFF.
To enter this state: Plug the amplifier into the AC line supply.
In this state: The front panel is dark. The internal auxiliary 5-V power supply is on.
The microprocessor is powered up and communicates via the USB port.
On (warmup)
Tube is warming up and HV is present.
To enter this state: Press the ON/OFF switch to ON.
In this state: The AC line is connected to the primary of the transformer and all
amplifier voltages are present (including the high voltage for the tubes).
A 3-minute warmup countdown begins, with LEDs lighting up sequentially along the
RF OUTPUT bargraph. The amplifier cannot be switched to Operate until the
countdown timer reaches 0. The number of seconds remaining is displayed in the
serial data.
During warmup, we recommend that you check the plate voltage by rotating the
multimeter selector switch to HV. The LED bargraph should show 3 kV.
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Table 5-1 Operational states (Continued)
State
Description
Standby
Tubes are ready and amplifier is in bypass mode (exciter only).
To enter this state: Wait for the amplifier to complete its 3-minute warmup.
5
In this state: The exciter can use the antenna, but the amplifier does not amplify the
signal. Certain faults cause the amplifier to return to this mode.
Operational but
unkeyed
Key-in has not been asserted.
To enter this state: Wait for the amplifier to complete its 3-minute warmup, then
press the OPER switch.
In this state: The amplifier is fully warmed up, but the key-in line has not been
activated. The exciter is still connected to the antenna.
Keyed, no RF
Key-in has been asserted, but no RF is sensed.
To enter this state: Wait for the exciter to short the key-in line to ground.
In this state: The input and output relays are activated, the tubes are biased on at a
very low current, the exciter is connected to the input of tubes, and the antenna is
connected to amplifier output.
Power
Amplifier is keyed, RF has been sensed, and amplifier delivers power.
To enter this state: Wait for the amplifier to sense RF.
In this state: The tubes are biased to the operational condition. The amplifier is now
fully operational and delivering power to the load.
IMPORTANT
!
To clear a fault:
• For a gain fault, wait for the amplifier to reset itself.
• For all other faults, resolve as described in Chapter 7,
“Diagnosing Faults and Troubleshooting.” Then move the
amplifier’s OPR/STBY switch to STBY and finally back to OPR to
continue.
5.2 Start Up the Amplifier
Procedure 5-1 Start up the amplifier
Page 5–2
Step 1
Install and set up the amplifier as described in the preceding chapters.
Step 2
Power up the amplifier by moving the OPR/STBY switch to STBY
(standby).
Step 3
Rotate the multimeter selector switch to HV.
Step 4
Press the POWER/ON switch.
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• The fan and blower begin to operate. If there is no air flow from the
amplifier and no sound of blower operation, immediately turn the
amplifier off and investigate.
• Within 2 seconds, the HV display moves all the way to the right,
certainly to more than 2500 V. If it is lower than this, investigate
further; the primary taps may not be correctly set.
• The red LED representing 1800-W output power lights up, indicating
the start of a built-in180-second countdown (1800/10 = 180 seconds).
As the timer counts down, the remaining time is indicated by the
currently lit LED on the power-output bargraph.
Step 5
Move the multimeter selector switch to Ip (plate current).
No current should be indicated during the entire warmup period. The
WAIT LED blinks about twice per second, indicating that warmup is still
in progress. The FAULT, OPER, and STBY LEDs remain unlit.
Step 6
Ensure that exhaust air is detectable from the exit vent holes above the
tubes. If exhaust air is not detectable:
6a TURN OFF the amplifier immediately.
6b Ensure that the exhaust chimneys are properly positioned over the
tubes.
6c Power up the amplifier again.
6d When the WAIT LED goes out and the OPR or STBY lights stop
blinking, indicating that warmup is complete, move the OPR/STBY
switch to OPR.
Step 7
Proceed to Section 5.3, “Tune the Amplifier,” page 5–3.
5.3 Tune the Amplifier
Each Alpha 8410 shipped from the factory includes a table showing the
tune and load settings that we used to achieve full output power on that
particular amplifier into an AP 2100 50-ohm dummy load. These settings
usually vary slightly from those in this guide.
Your goal in tuning the amplifier is to maximize output power for a given
input power.
Any linear amplifier must be adjusted for optimum efficiency and
linearity at each specific power level. Operation at higher or lower power
results in the following:
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The following occur:
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• Operation at higher power without appropriate readjustment results
in flat-topping, also known as “splatter,” and (usually) excessive
amplifier grid current.
• Operation at lower power results in decreased amplifier efficiency.
5
Recommended practice is to tune first into a dummy load or artificial
antenna, then connect the antenna and make any slight final adjustments
that may be needed.
For any frequency where antenna VSWR is >1.5:1, it is important to
carefully tune the amplifier for a proper match.The Alpha 8410 does not
contain an antenna tuner. The SWR can be tuned via the antenna or an
external tuner connected to the amplifier output. Nevertheless, at SWR of
<2:1, the additional RF power loss of an antenna tuner can be avoided by
tuning the amplifier into the slight mismatch. There is no advantage to
using a tuner to tweak” the last bit of SWR; in fact, you lose power this
way.
The Alpha 8410 senses the beginning of any RF arc in, for example, a
TUNE or LOAD variable capacitor and automatically switches the
amplifier to standby within a few milliseconds.This system has virtually
eliminated RF arc damage in current Alpha amplifiers. The system
similarly detects severe mistuning and, if drive exceeds ~25 W, switches
the amplifier to standby. The 25-W input trip threshold permits safe
tuning at low power levels without aggravating and unnecessary trip-outs.
REMEMBER
Remember
A properly tuned amplifier has the following properties:
• Full legal power output:
— For voltage SWR <2.0:1, normal value is 1500 W (with 40–60
W drive).
— For SWR > 2.0.1, full output may not be possible but the other
tuning indications are the same.
• Grid-current green LED either lit or unlit.
• Gain indication in right half of bargraph.
• Plate current normal value of 1 A at 1500 W. (The system alarms
at values exceeding 1.2 A.)
!
CAUTION
CAUTION! If, at any time in the following procedure, the amplifier
fails to respond as described, do the following:
1. Remove drive immediately.
2. Turn the OPR/STBY switch to STBY.
3. Verify all connections and cables.
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4. Turn the OPR/STBY switch to OPR.
5. Proceed with the tuning procedure.
Tuning by the
Recommended Dipand-Load Method
5
This is our recommended way to tune the amplifier.
Procedure 5-2 Tune by the recommended dip-and-load method
Step 1
Start up the amplifier as described in “Start Up the Amplifier,” page 5–2.
Step 2
Set the BAND, TUNE, and LOAD controls to the values given in your
amplifier’s specific tuneup table. Note that final TUNE and LOAD
settings will vary with operating frequency, antenna characteristics, and
power level.
Step 3
Please limit the transceiver drive to ~65 W for tuning and operating the
amplifier.
Step 4
Move the multimeter selector switch to Ip (plate current).
Step 5
Set the TUNE and LOAD controls to the values given in your amplifier’s
specific tuneup table.
Step 6
Key the amplifier with 20 W drive and adjust the TUNE control for a peak
in RF out that should be at the same point as a dip in Ip.
Step 7
Increase the drive to get 1000 W output, going back and forth between
TUNE and LOAD to peak the RF output. If more output is desired,
increase drive from the amplifier slightly, increase LOAD for a peak in
RF out, then peak RF out with TUNE control.
When the amplifier is tuned correctly on 160 through 40 m, the following
should be the case:
• The Ip should range between 0.9A and 1.1 A (read on the 0–1.5-A
scale) for 1500 W output.
• The input-drive power should not be more than ~60 W.
• On 20 m, the Ip is usually ~1.0 A for 1500-W output.
Plate current (Ip) is the most useful parameter to monitor on the
multimeter bargraph during normal operation.
Step 8
Tuning by the Alternate
Nominal-Gain Method
Proceed to “Operate the Amplifier,” page 5–7.
This is an alternative way to tune the amplifier.
Procedure 5-3 Tune by the alternate nominal-gain method
Step 1
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5
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Step 2
Set the BAND, TUNE, and LOAD controls to the values given in your
amplifier’s specific tuneup table. Note that final TUNE and LOAD
settings will vary with operating frequency, antenna characteristics, and
power level.
Step 3
Reduce the transceiver carrier output control to 0.
Step 4
Move the OPR/STBY switch to OPR (operate).
The OPR LED lights up.
Step 5
On the multimeter selector-switch bargraph, select the GAIN function.
Step 6
Switch the transceiver to CW and increase its carrier output to ~15 W (the
amplifier output will be ~300–500 W).
Step 7
Do the following:
7a Adjust the TUNE control to deflect the GAIN LED maximum
rightward.
7b Adjust the LOAD control to place the illuminated GAIN LED
between the white lines above and below the LED bargraph.
Repeat this step at least twice.
Step 8
Increase the excitation power until the amplifier output is ~1500 W.
Step 9
Do the following:
9a Adjust the TUNE control to deflect the GAIN LED maximum
rightward.
9b Adjust the LOAD control to place the illuminated GAIN LED
between the white lines above and below the LED bargraph.
Step 10
Touch up the TUNE control for maximum power output.
The amplifier is now correctly tuned to deliver 1500 W RF output on SSB,
CW, FSK, SSTV, and FM.
The GAIN LED normally fluctuates during modulation or keying. If the
first red LED on the RF OUTPUT bargraph lights, output exceeds 1500
W. It is normal for the GAIN LED to vary during standard operation,
especially for SSB.
Step 11
Page 5–6
Proceed to “Operate the Amplifier,” page 5–7.
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Procedure 5-4 Operate the amplifier
55
Step 1
Start up and tune the amplifier as described in “Start Up the Amplifier,”
page 5–2 and “Tune the Amplifier,” page 5–3.
5
Step 2
Apply RF.
5.4 Operate the Amplifier
The amplifier requires only ~50 W for full output.
Step 3
Ensure that exhaust air is detectable from the exit vent holes above the
tube. If exhaust air is not detectable:
3a TURN OFF the amplifier immediately.
3b Ensure that the exhaust chimneys are properly positioned over the
tubes.
3c Power up the amplifier again.
3d When the WAIT LED goes out and the OPR or STBY lights stop
blinking, indicating that warmup is complete, move the OPR/STBY
switch to OPR.
Step 4
Monitor grid current.
The amplifier operates in Class AB1 when delivering maximum output
power consistent with excellent linearity. A small amount of grid current
flows, which you can monitor as follows:
• The GRID MIN LED lights up green as drive approaches the
optimum level.
• The GRID LED flickers green on SSB voice peaks and lights up
under CW/SSTV/RTTY carrier conditions.
• The GRID MAX LED does the following:
• Lights dim red at maximum output and efficiency
• Lights full red as overdrive approaches
For SSB operation, optimum output consistent with good linearity occurs
when the GRID LED lights up green on most voice peaks and the GRID
MAX LED flickers dim red on only the highest peaks.
Excessive grid current results from overdrive and/or inadequate loading.
The solution is to restrict drive and/or increase amplifier loading. The
amplifier’s VTX-X120 tubes are well protected and these adjustments
tend to be less critical than in many other amplifiers. Grid bias is
stabilized against grid current fluctuations.
Step 5
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Monitor plate current.
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In the event of grossly excessive plate current or fault in the high-voltage
circuitry, the plate-current relay quickly turns the amplifier off. However,
the relay does not prevent tube or other damage due to either short-term
or long-term overdrive or improper tuning. It is your responsibility to
ensure safe tuning, drive, and general operating conditions.
5
If the overcurrent relay trips, remove AC power from the amplifier, then
determine and correct the cause of the trip before turning the amplifier
back on. This hard-fault trip circuit does not rely on the microcontroller
for its operation, and protects the amplifier under all conditions, even if
the processor is damaged or malfunctioning.
Idling plate current for the Alpha 8410 is ~350–400 mA during full-power
transmission. A detector senses RF drive, and, during pauses in speech
and key-up intervals, reduces plate current to 30–50 mA, substantially
reducing average power supply loading, heat generation, and wasted
energy.
NOTE
Page 5–8
If the amplifier faults, it usually resets itself after 4 seconds. For
information about faults, see Chapter 7, “Diagnosing Faults and
Troubleshooting.”
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6 Maintaining the Amplifier
6.1 Clean the Amplifier Chassis 6–1
6.2 Replace Tubes and/or Fuses 6–2
6.3 Retune the Amplifier 6–3
IMPORTANT
!
• The Alpha 8410 is extremely easy to set up, operate, and
maintain. However, failure to carry out each procedure exactly as
described in this manual is likely to lead to amplifier damage,
which is not covered under warranty. Damage to other station
equipment may also result.
• Do not apply oil or grease to any amplifier components. There are
no user-accessible lubrication points in the amplifier.
• The amplifier is equipped with a cover interlock switch that
removes primary power from the amplifier and a crowbar that
short-circuits high voltage to the chassis when the cover is lifted.
These interlocks protect against electric shock resulting from
accidental contact with the lethal voltages inside the amplifier.
The cover interlock is intended only as backup protection against
accidents. Never depend on it! Always disconnect the power cord
from the AC mains before removing the cover.
IMPORTANT: Do not disable the interlock switch for any
reason.
6.1 Clean the Amplifier Chassis
Perform this procedure at least once a year.
Procedure 6-1 Clean the amplifier chassis
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Step 1
Power down the amplifier.
Step 2
Clean the exterior with a mild liquid detergent. Do not use chemical
solvents, as these may severely damage the front panel or cabinet finish.
Never use an abrasive cleaner.
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!
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WARNING
WARNING! Do not allow any liquids to enter the cover’s tubeexhaust holes.
6
Step 3
Disconnect the AC line cord from the power source and lift the cover.
!
WARNING
WARNING! Disconnect the AC line cord from the power source
before lifting the cover for any reason.
Step 4
Clean the interior, particularly high-voltage areas, with a vacuum cleaner
and a soft bristle brush frequently enough to prevent visible accumulation
of dust. Optimally, remove the plate under the tube deck (attached with 4
screws) and use compressed air to blow out the cooling fins in the tubes.
Step 5
If conditions are extremely dusty, secure a thin air filter of the type used
for window air conditioners across the air intake on the rear panel.
Step 6
Replace the cover and reconnect the AC line cord to the power source.
6.2 Replace Tubes and/or Fuses
Perform this procedure only as needed.
Procedure 6-2 Replace tubes and/or fuses
Step 1
Power down the amplifier.
Step 2
Disconnect the AC line cord from the power source and lift the cover.
!
WARNING
WARNING! Before lifting the cover for any reason, disconnect the
AC line cord from the power source.
Step 3
Replace tubes as needed. Ensure that cooling airflow to the tubes is
sufficient.
Use a matched pair of high-quality VTX-X120 tubes.
Step 4
Replace fuses as needed.
For 190–220-VAC service, use only 20-A, 250-V-rated fuses. For
90–130-VAC service, you may optionally use 25-A fuses with caution.
IMPORTANT: Never replace a fuse with one of a different
type or greater current rating. Damage resulting from
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Maintaining the Amplifier
Blowing of one or both primary-line fuses indicates that the maximum
safe average power capability of the amplifier has been substantially
exceeded or that an equipment failure has occurred.
The slow-blow fuse (F3), located below the primary-line fuses, may
prevent damage to the step-start resistors and HV rectifiers in the event of
abnormal turn-on conditions or HV faults. If the AC interlock is defeated
and primary power is applied while the HV crowbar is closed, the stepstart fuse normally blows.
Step 5
Replace the cover and reconnect the AC line cord to the power source.
6.3 Retune the Amplifier
Normally you need to retune the amplifier only if you change radios,
antennas, or some other aspect of your shack.
Your objective in tuning the amplifier (and the drive applied to it) is to
obtain optimum efficiency and linearity at the desired output power. You
must adjust the amplifier for optimum efficiency and linearity at each
specific power level. If you attempt to operate at higher or lower power
levels than those for which you have adjusted, the following happens:
• At higher power, the amplifier flattops, splatters, and (usually)
produces excessive amplifier grid current.
• At lower power, the amplifier decreases efficiency considerably.
For instructions on retuning the amplifier, see Section 5.3, “Tune the
Amplifier,” page 5–3.
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use of a fuse of incorrect size or type is not covered
under and may void the warranty.
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6
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7
7 Diagnosing Faults and Troubleshooting
7.1 Diagnose Faults 7–1
7.2 Troubleshoot Problems 7–4
7.1 Diagnose Faults
If the amplifier encounters unsafe operating conditions, it enters a
protective fault mode and faults into STBY or OFF. The OPR LED goes
off and the FAULT and STBY LEDs go on.
When this happens, the tubes are biased off and the relays are placed in
bypass mode, causing RF from the radio to go directly to the antenna. The
FAULT LED on the front panel flashes on and off for ~4 seconds. After
this period, unless the OPER/STBY switch has been placed in the STBY
position, the amplifier attempts to return to OPERATE mode. You can
shorten this 4-s period by toggling the OPER/STBY switch.
While the FAULT LED is flashing, the Ip and HV LEDs indicate which
fault type caused the amplifier to enter fault mode. Fault-type codes are
also reported in the amplifier telemetry data via the USB port on the rear
of the amplifier. These fault types are summarized in Table 7-1 and
described in the following text.
Table 7-1 Fault types
Fault type
LED behavior
Ip LED
1
Blinking Blinking Amplifier gain is below 10 dB.
2
3
4
Cause
HV LED
Dark
Dark
Plate current in the tube exceeds
1.5 A.
Blinking Reflected power is too high.
Dark
Input-drive power is too high.
5*
Plate current exceeds 2.5 A.
6*
Plate current was detected during
warmup.
* Faults 5 and 6 do not display on the front panel. Rather, they indicate
only through telemetry via the USB port.
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Fault type 1
7
LED behavior
Both Ip and HV LEDs are blinking.
Cause
Amplifier gain has fallen to <10 dB.
This is an important safety feature of the amplifier, as many different
problems can be detected as a drop in gain. So that this fault does not
occur while the amplifier is being tuned, gain fault detection is disabled
when drive power to the amplifier is below ~20 W. This allows correct
initial amplifier tuning to be achieved before going to full power.
Resolution
1. Reduce the input-drive power.
2. Retune the amplifier.
Fault type 2
LED behavior
Cause
Resolution
Ip LED is blinking.
Plate current in the tube has exceeded 1.5 A. If the current exceeds
~2.5 A, AC select relays are de-energized and the amplifier shuts off
completely.
1. Retune the amplifier.
2. Ensure that the amplifier is not overdriven.
3. Fix any problems in the bias-control circuitry.
4. If the amplifier has shut off, wait at least 20 seconds, then use the ON/
OFF switch to turn the amplifier back on.
5. If the amplifier trips again immediately, investigate and resolve the
problem before attempting to turn the amplifier on again.
DO NOT repeatedly hit the ON switch when the amplifier trips out.
Doing so is likely to result in severe damage to amplifier components.
When you are certain that you have taken care of the problem that
caused the fault, you may turn the amplifier back on.
Fault type 3
LED behavior
Cause
HV LED is blinking.
Reflected power is too high.
The amplifier trips when reflected power exceeds ~250 W. At 1500-W
output, this represents a voltage standing-wave ratio (VSWR) fault
exceeding 3:1.
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Alpha 8410 Linear Amplifier User Manual
Diagnosing Faults and Troubleshooting
1. Check the output coaxial cable and connectors; replace or reconnect
as needed.
2. Check the antenna SWR using an external wattmeter or by putting the
amplifier in standby mode and using the SWR meter on your
transceiver. Make adjustments as needed.
Fault type 4
LED behavior
Cause
Neither Ip nor HV LED is blinking; both are dark.
Input-drive power is too high.
The amplifier behaves as follows at various input-drive power levels:
• When power is below 75 W, the amplifier operates normally.
• When power spikes above 75 W, a 500-ms timer starts, during which
time the power threshold is reduced from 75 to 65 W. If you do not
reduce the power to below the threshold at the end of 500 ms, Fault 4
results.
• When power exceeds 100 W (the absolute maximum value at which
the amplifier can operate), an immediate Fault 4 results.
Resolution
Decrease the input-drive power.
Fault type 5
LED behavior
Cause
Resolution
The amplifier shuts off and goes to State 0.
A hard fault has occurred because input-drive power exceeded 125 W,
causing plate current to exceed 2.5 A (Ip > 2.5 A).
Decrease the input-drive power or retune the amplifier.
Fault type 6
LED behavior
Cause
Resolution
The amplifier shuts off and goes to State 0.
A hard fault has occurred because significant plate current was detected
when the amplifier was warming up or was unkeyed (States 1–3). The
threshold for this fault is one-third of the value for a “soft” Ip trip, or
533 mA.
1. After the amplifier shuts off, wait at least 20 seconds, then use the
ON/OFF switch to turn the amplifier back on.
IMPORTANT: When the amplifier trips out, DO NOT
repeatedly press the ON/OFF switch to attempt to turn
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Resolution
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the amplifier back on. Doing so is likely to result in severe
damage to amplifier components.
2. If the plate current again starts to rise while the amplifier is warming
up, investigate and resolve the problem before attempting to turn the
amplifier on again.
7
3. Fix any problems in the bias-control circuitry.
4. When you are certain that you have taken care of the problem that
caused the fault, turn the amplifier back on.
7.2 Troubleshoot Problems
Amplifier does not turn on;
nothing happens when the
ON switch is pushed
1. External AC wiring, a fuse, or a circuit breaker may be open. Check
and correct wiring, replace fuse, or reset circuit breaker.
2. The amplifier cover may not be in place or properly secured or the
cover safety interlock may be open. Ensure that the cover is in place
and all screws are securely inserted.
3. One or more connectors may be loose. Check that all of the
transformer connectors are securely attached, that the 3x3 molex
connector at the back of the amplifier is fully engaged, and that the
two connectors between the transformer and the HV power supply
boards are firmly inserted.
4. Fuse F1–F3 may be open or missing. Check fuses with an ohmmeter.
Replace any blown fuses with fuses of the same size.
5. The step-start resistor may be open. Check the resistor. If it is
damaged, replace it.
Amplifier turns on but no HV
is indicated by the multimeter
LED bargraph
1. The multimeter selector switch may be in the wrong position
(example: Ip). Set the switch to the correct position.
2. The transformer may be plugged into the power supply incorrectly.
Check the power-supply wiring and connectors to ensure that the
input and output connectors and the voltage taps are set properly.
3. An HV circuit fault may exist. Check the line voltage.
4. The HV sampling resistor in the power supply may be damaged.
Contact RKR Designs technical support.
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The plate voltage to the power supply may be too low. Check the line
voltage and confirm that the tap is set correctly.
77
Amplifier turns on but HV
reading is low as indicated on
the multimeter bargraph
Alpha 8410 Linear Amplifier User Manual
Diagnosing Faults and Troubleshooting
7
Amplifier turns on but time
delay does not complete and
WAIT LED does not turn off
The timing circuitry on the control board may be damaged or defective.
Contact RKR Designs technical support.
Amplifier turns on and time
delay completes but amplifier
does not transmit
The T/R control-line (key-line) connection to the amplifier may be faulty.
1. Confirm that the key line is inserted into the correct jack on the back
of the amplifier.
2. Confirm that the key line is connected to the correct port on the
transceiver and that amplifier-keying is enabled.
3. If the tube current has exceeded 2.5 A, follow the resolution
instructions for “Fault type 2,” page 7–2 and “Fault type 5,”
page 7–3.
4. Confirm that the cable is good.
5. Confirm, with the multimeter switch in the Ip position and the
amplifier keyed with no RF, that plate current is drawn.
Amplifier operates properly,
then turns off completely
The tube current may exceed ~2.5 A. See the resolution instructions for
“Fault type 4,” page 7–3.
Amplifier transmits but red
GRID LED lights often
The amplifier may be overdriven or incorrectly tuned; most likely the load
control is set too low. Reduce the transceiver output and adjust the tune
and load controls to maximize efficiency with minimum grid lights.
When switching from STBY to
OPR mode, receive signals
disappear or are severely
attenuated
1. The RELAY (T/R) control cable from the transceiver may be shorted.
Check the cable to ensure that it is switching properly. Replace it if
needed.
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2. The transceiver may be locked in transmit. Ensure that the transceiver
is properly switching between TRANSMIT and RECEIVE modes.
For assistance, see the transceiver manual.
7
When amplifier is in STBY or
RECEIVE mode, plate current
is indicated
Distorted SSB signal; grid
bias is unexpectedly
decreasing
The tube bias supply or T/R bias switch may be faulty. Contact RKR
Designs technical support.
1. The RF drive from the transceiver may be excessive and/or amplifier
loading may be insufficient. Decrease drive from the transceiver.
Recheck the amplifier tuning.
2. The coaxial connector, coax feed line, antenna feed point balun,
tuner, or antenna trap may be arcing on voice peaks. Replace the
faulty components.
3. RF feedback may exist from the antenna into the transceiver via the
transceiver power cord, microphone or key cable, or other unshielded
station patch cables. Ensure that all power cords, microphone and key
cables, and other cables are properly shielded and grounded.
4. The station RF ground may be poor. Ensure that the amplifier and
transceiver have a proper RF ground.
Required drive to maintain
1500 W is steadily increasing
Page 7–6
The tubes may be aging. Contact RKR Designs technical support to
determine whether the tubes need to be replaced.
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Terminology
Terminology
NOTE: For detailed explanations of the following terms, see various publications including the latest
American Radio Relay League (ARRL) Handbook.
A
AB1 — Modulation class AB1. Class that provides
good linearity in a push-pull configuration.
AC — Alternating current. Electric current whose
magnitude and direction vary with time.
ALC — Automatic Level Control. Technology
that automatically controls output power.
ampere — Unit of electric current.
ARRL — American Radio Relay League. US
national organization of amateur radio
operators. For more information, go to
www.arrl.org.
AWG — American wire gauge. Standard method
of denoting wire diameter.
B
B1 — Modulation class AB1. Amplifier-circuit
class that provides good linearity in push-pull
configuration.
C
CW — Continuous wave. Electromagnetic wave
of constant amplitude and frequency.
D
dB — Decibel. Logarithmic unit of measure of the
power of sound relative to a reference level.
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E
EBS — Electronic bias switching. A form of
switching that increases negative grid 1 voltage
in pauses in speech or between Morse code
elements, resulting in reduced standing bias on
the tubes.
exciter — Radio that provides RF drive for the
amplifier to operate. The transmitter portion of
the transceiver.
F
FCC — Federal Communications Commission.
For more information, go to www.fcc.gov.
FM — Frequency modulation. Modulation scheme
in which information is conveyed over a carrier
wave by variations in frequency.
FSK — Frequency-shift keying. Type of
frequency modulation in which information is
conveyed by shifts in the output frequency
between predetermined values.
H
HF — High frequency. Radio frequency within the
range 3–30 MHz.
HV — High voltage. Electrical circuit in which the
voltage used presents risk of both electric shock
and electrical arcing.
Hz — Hertz. One periodic event per second.
I
Ip — Idling plate current. Plate current measured
when the amplifier is keyed and RF is not
present.
K
key — Signal from the radio to the amplifier that
instructs the amplifier to switch from receive to
transmit mode because the radio is ready to
generate RF power. The (programmable) delay
between keydown and RF out is generally 8–12
ms. When the amplifier is keyed, it is in State 5.
Page Term–2
kV — Kilovolt. 1000 V.
kVA — Kilovolt-ampere. 1000-W capability.
kVA * 0.8 = kilowatts.
kW — Kilowatt. 1000 W.
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Terminology
L
LED — Light-emitting diode. Semiconductor
diode that emits incoherent narrow-spectrum
light, providing a form of electroluminescence.
LV — Low voltage. Electrical circuit in which the
voltage used presents risk of electric shock but
only minor risk of electrical arcing.
M
mA — Milliampere. 10–6 A.
MHz — Megahertz. 106 Hz.
O
OPR — Operate.
PCB — Printed circuit board. Board that
mechanically supports and electrically connects
electronic components.
P
PSK — Phase-shift keying. Digital modulation
scheme in which information is conveyed by
changes, or modulations, in the phase of a
reference signal.
Q
QSK — Quadrature-shift keying. Digital
modulation scheme in which the transmitter is
on only for the duration of each dot or dash and
switches to receive between each dot or dash,
allowing the operator to hear any signal being
sent.
R
RCA — Radio Corporation of America. Also a
type of interconnecting plug.
RF — Radio frequency. Frequency within the
range 3 Hz–300 GHz.
RG-x/x — Coaxial cable type.
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RMS — Root mean square. Statistical measure of
the magnitude of a varying quantity such as a
wave.
RTTY — Radio teletype. Telecommunications
system consisting of two or more teleprinters
using radio as the transmission medium.
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RKR Designs LLC
S
SSB — Single sideband. Modulation scheme that
refines upon amplitude modulation.
SSTV — Slow-scan television. Picturetransmission method for transmitting and
receiving static pictures via radio.
STBY — Standby. Mode in which an electronic
appliance is turned off but under power and
ready to activate on command.
SWR — Standing-wave ratio. Ratio of the
amplitude of a partial standing wave at an
antinode (maximum) to the amplitude at an
adjacent node (minimum). Measure of antenna
and feedline efficiency.
T
T/R — Transmit /receive.
transceiver — Device that has both a transmitter
and a receiver within the same circuitry or
chassis.
U
UHF — Ultra-high frequency. Radio frequency
US — United States.
within the range 300–3000 MHz (3 GHz).
V
VAC — Volts of alternating current.
VDC — Volts of direct current.
Page Term–4
VSWR — Voltage standing-wave ratio. Example:
If VSWR = 1.2:1, the maximum standing-wave
amplitude is 1.2 times greater than the
minimum standing-wave amplitude.
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Schematics
Schematics
NOTE: The following pages contain detailed schematics for the Alpha 8410 linear amplifier.
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