QRO Technologies HF-2000 User manual

QRO HF-2000 LINEAR AMPLIFIERQRO HF-2000 LINEAR AMPLIFIER
INSTRUCTION MANUAL
QRO TECHNOLOGIES, INC.QRO TECHNOLOGIES, INC.
1117 West High Street
P.O. Box 939
Bryan, OH 43506 USA
Tel & Fax: [phone]
E-Mail: [email protected]
Internet: http://www.qrotec.com
PUBLICATION DATE: JUNE 1995
COPYRIGHT 1995 BY QRO TECHNOLOGIES, INC. ALL RIGHTS RESERVED.
THIS MANUAL OR ANY PART THERE OF MAY NOT BE REPRODUCED IN ANY FORM WITHOUT
PERMISSION FROM QRO TECHNOLOGIES, INC.

2
SPECIFICATIONS
Band Coverage: 160, 80, 40, 20, 17, and 15 (12 & 10 export only) meter
amateur bands. 12 & 10 meter also useable in USA with
proof of license and user modification.
Drive Power Required: 120 Watts Typical
Maximum Output Power: 1,500 Watts SSB, 1250 Watts CW, 800 Watts RTTY, FM,
SSTV
Duty Cycle: 100% SSB Continuous Voice Modulation
80% CW
50% RTTY, FM, SSTV.
Continuous Carrier (Dead Key) 15 minute time limit at 800
watts with Auxiliary cooling
Automatic Limiting
Control (ALC):0 to -20 Volts negative going, adjustable from Front Panel
Harmonic Suppression: 2nd at least -45 db; 3rd - 10th at least -50db
Keying: Requires contact closure or sink of +12 VDC @ 80 ma
Input Impedance: 50 ohms unbalanced
Output Impedance: 50 ohms unbalanced with SWR 2:1 or less
Tube Requirement (2): 3-500Z, 3-500ZG, 3-500C
Power Line Requirement: 120 VAC, 50/60 Hz at 20 amperes maximum
240 VAC, 50/60 Hz at 10 amperes maximum
Front Panel: Multimeter (Plate Voltage, Plate Current, Power
(See Front Panel Pictorial) Output PEP, Relative ALC)
Grid Current Meter
Multimeter Function Switch
Transmit LED Indicator
Power LED Indicator
Power On/Off Switch
Tune & Load Controls with 6-1 Reduction Drives
Bandswitch
Rear Panel: RF Input (SO-239)
(See Rear Panel Pictorial) RF Output (SO-239)
Transmit Keying Line (RCA Phono Socket) or
+15 V Supplied by Transceiver on Transmit (RCA Phono Socket)
ALC Output (RCA Phono Socket)
Tuned Input Adjustments (160, 80, 40, 20, 17, 15,
12, and 10 meters)
Ground Post
Fuses (two 20 ampere for 100/120 VAC or two 10
ampere for 200/240 VAC)
Dimensions: 18w x 15d x 8-1/2h (Inches)
45.7w x 38.1d x 21.6h (Centimeters)
Net Weight: 76 lbs. or 34.5 kgs.

3
TABLE OF CONTENTS
Warranty 4
Proprietary Notice 4
Safety Notification 5
Unpacking & Inspection 6
Transformer & Tube Installation 6, 7
Line Voltage Selection Power Block Wiring 7
Reshipment Instructions 7, 8
Introduction 8
Location 7
AC Power Line Considerations 8,9
Antenna 9
Grounding 9
Equipment Interconnections 10
Safety Interlock Switch 10
Driving Power 10
Tube 11
Reading the Meters 11
Tune-Up Procedure 11,12
Using the ALC Adjust Control 13
Tuned Input Adjustments 13, 14
Periodic Maintenance 14
Troubleshooting Chart 15-18
Circuit Descriptions 18-22
Addendum #1 Power Block Wiring
Addendum #2 Schematics
Addendum #3 PCB Layouts
Addebdum #4 Front & Rear Panel
Pictorials

4
WARRANTY
_____________________________________
The HF-2000 is warranted against defects in material and workmanship for a period
of two years for the original date of sale. This warranty does not cover the 3-500
triode which carries a separate warranty issued buy its manufacturer. Please check
the warranty card which comes with the tube. During the warranty period, QRO
Technologies, Inc. will repair or replace the amplifier at our option if it is defective in
any way in material and workmanship. The warranty does not cover any defects
resulting from improper use by the buyer or inadequate maintenance. In such cases
the repair will be billed at prevailing service rates.
For warranty service or repair, the amplifier must be returned to the factory for
authorized service. The buyer shall prepay shipping and insurance charges, QRO
Technologies, Inc. will pay shipping and insurance charges to return the amplifier to
the buyer. Please call the factory at 1-800-956-2721 for shipping instructions. Make
sure when returning the amplifier you have insured the instrument for the full
replacement cost. QRO Technologies, Inc. is not liable for any damage incurred
during return shipments.
PROPRIETARY NOTICE
_____________________________________
This instruction manual, schematic diagrams, and technical data herein disclosed,
are proprietary to QRO Technologies, Inc. and shall not, without express written
permission of QRO Technologies, Inc.. be used, in whole or part to solicit quotations
from a competitive source or used for manufacturing by anyone other than QRO
Technologies, Inc. The information herein has been developed at private expense,
and may only be used for operation and maintenance reference purposes or for
purposes of engineering evaluation and incorporation into technical specifications
and other documents which specify procurement of products from QRO
Technologies, Inc. This amplifier is covered by copyrights both in the United States
of America and throughout the world.

5
ALWAYS THINK
SAFETY
__________________________________________________
THIS LINEAR AMPLIFIER DESCRIBED IN THIS MANUAL CONTAINS VOLTAGE
HAZARDOUS TO HUMAN LIFE AND SAFETY WHICH IS CAPABLE OF
INFLICTING PERSONAL INJURY. NEVER OPERATE THE AMPLIFIER WITH THE
TOP COVER REMOVED AND THE TOP COVER SAFETY SWITCH DEFEATED.
BEFOREREMOVING THE TOP COVER MAKE SURE THE AC LINE POWER
CORD HAS BEEN DISCONNECTED FROM THE AC POWER SOURCE. ALLOW
AMINIMUM OF 5 MINUTES TO ELAPSE BEFORE REMOVING THE TOP
COVER AFTER POWER HAS BEEN REMOVED. THIS IS NECESSARY TO
ALLOW THE PLATE VOLTAGE FILTER CAPACITORS TO BLEED DOWN TO A
SAFE LEVEL.
If this amplifier is to be powered from the AC line (mains) through an autotransformer (such as
a Variac or equivalent) ensure that the common connector is connected to the neutral (earth pole)
of the power supply.
Before operating this unit ensure that the protection conductor (green wire) is connected to the
ground (earth) protective conductor of the power outlet. Do not defeat the protective features of
the third protective conductor in the power cord by using a two conductor extension cord or a
three-prong/two-prong adapter.
Before operating this unit:
1. Ensure that the instrument is configured to operate on the voltage available
at the power source. (See Installation Section)
2. Ensure that the proper fuses are in place in the amplifier's AC line fuse holders located
on the rear panel.
3. Ensure that all other devices connected to or in proximity to this amplifier are properly
grounded or connected to the protective third-wire earth ground.
If at any time the amplifier shows visible damage, has sustained stress, emits a foul smell,
fails to operate satisfactorily, it should not be used until its performance has been checked
by qualified service personnel.

6
UNPACKING AND INSPECTION
The amplifier is shipped in three cartons: amplifier, transformer, tube. Before unpacking each
carton, check the exterior of the shipping carton for any sign of damage. All irregularities should
be noted. Unpack and remove each component carefully from its carton, preserving the factory
packaging as much as possible. Inspect each component for any noticeable defect or damage.
Notify QRO Technologies if any defect or damage is apparent.
TRANSFORMER AND TUBE INSTALLATION
Before performing any of the following installation procedures, make sure that the amplifier
has not been plugged into the AC supply line.
The Amplifier is shipped with the tubes and transformer each shipped in a separate carton. As
part of the installation process, you must install the tube and transformer. You will need the
following tools:
1. Phillips Screwdriver
2. Awl or suitable hole alignment tool
3. Adjustable wrench
Remove the Amplifier's top cover by removing the nine 6-32 x 3/8 Phillips Head machine screws
and their associated flat washers. The sides of the top cover may bend outward when the screws
are removed. This is normal, and they will return when you replace the screws and washers.
TRANSFORMER: Remove the transformer from its shipping carton. You will notice two
connectors on the ends of the transformer leads. The smaller connector is for the primary leads,
and the larger connector is for the secondary leads. Position the amplifier so the front panel is
facing you. Position the transformer so the primary leads are on your left and the secondary leads
are on your right.The amplifier's transformer compartment should be on the right side. Observe
there are matching primary and secondary leads coming from the amplifier. The primary leads
originate on the back panel, and there are three black leads and three white leads. The nine
secondary leads originate from the center divider panel. The primary and secondary leads of the
transformer and amplifier have matching "mate & lock" connectors. Place the transformer into the
transformer compartment with the secondary leads on the right and the primary leads on the left.
The transformer's four mounting holes should align with the four mounting screws coming out of
the amplifier's bottom panel. Secure the transformer with two 1/4-20 hex nuts on the two right side
mounting screws. Connect the primary and secondary "Mate & Lock" connectors together. Each
connector is indexed so they connect only one way, and you will hear a distinctive click when the
are correctly mated. Make sure the primary leads coming from the transformer do not
obstruct or prevent the free movement of the cooling fan. Check to see if the step-start
relay contact arm, located on the rear panel just above the cooling fan, has not been placed
out of position during installation. Make a check of all chassis wiring around the
transformer to make sure no wiring has been pinched by the transformer's mounting plate.
Correct any observed problems.
TUBE: The tube sockets are located on the left side of the amplifier. They have five contacts

7
which match the five pins on the 3-500 triode. Insert the tube into the socket making sure that the
pins align with the socket contacts. If the tube pins and socket contacts are not aligned, the
amplifier will not function properly and damage to the tube may result. After you have properly
inserted the tube into its socket, connect the parasitic suppressor choke coming from the top of
the plate choke to the plate connector pin located on the top of the tube. The connector should
snugly slide over the plate connector pin.
LINE VOLTAGE SELECTION POWER POWER BLOCK WIRING
Before performing any of the following installation procedures, make sure that the amplifier
has not been plugged into the AC supply line.
Refer to the four Power Block Wiring Diagrams while reading this section. Locate the Line Voltage
PowerBlock. It is located inside the just above the AC line Cord, and it contails 6 screw
connection termials. It also has black and white leads connected to it.
120 VAC: Two wire jumpers (J1 & J2) are connected to terminals. J1 is connected to terminals
1 & 4. J2 is connected to terminals 2 & 5. If there is a white wire connected to left side of terminal
6, remove it an connect it to left side of terminal 5. Also, if there is a black wire connected to the
left side of terminal 3, remove it and connect it to the left side of terminal 2. Remove the small
black wire connected to the right side of terminal 3 and connect it to the right side of terminal 2.
Make sure all screws are tightened.
240 VAC: One wire jumper (J1) is connected to terminals. If a second Jumper was previously
connected to the terminal block, you make discard it. J1 is connected to terminals 2 & 4. If there
is a white wire connected to left side of terminal 6, remove it an connect it to left side of terminal
5. Also, if there is a black wire connected to the left side of terminal 3, remove it and connect it
to the left side of terminal 2. Remove the small black wire connected to the right side of terminal
3 and connect it to the right side of terminal 2. Make sure all screws are tightened.
You are now ready to replace the amplifier's top cover. The hot air exhaust holes should be
located on the top left and the cooling air entry holes should be on the right side. Align the
mounting holes with the corresponding threaded inserts located on the chassis. You may also
need to use an alignment tool such as an awl. You may need to lightly tap the top cover into place
with your hand. The left and right sides of the top cover may need to be pushed inward as you
place the mounting screws into place. Replace the nine 6-32 x 3/8 mounting screws and washers.
Partially tighten each screw. When all nine screws have bee inserted, tighten all the screws.
Double check to make sure that the cooling air entry holes are on the right side , and the
hot exhaust air exit holes are located on the top left directly over the tube.
RESHIPMENT INSTRUCTIONS
Use the original packaging if it is necessary to return the amplifier, transformer, or tube to QRO
for servicing. The original shipping carton and the interior corner pads are designed to provide
the necessary support for safe shipment or reshipment. If the original carton along with the
internal packaging is not available, contact the factory and a new carton will be shipped to you
at a nominal cost. Always insure the package for the full replacement value and ship via UPS
ground service. QRO Technologies, Inc. will not be responsible for any damage or loss

8
during return shipment.
INTRODUCTION
The QRO Model HF-2000 Linear Amplifier is a completely self-contained, grounded grid, linear
amplifier. It is designed to operate at 1,500 watts PEP output on SSB, 1250 watts on CW, and
1000 watts on such high duty cycle emissions as RTTY, SSTV, and FM. The HF-2000 is designed
to be used with any transceiver which will deliver 120 watts or more output. It can be used with
less driving power, but it will have a lower output. A broad-band tuned input circuit for each band
feeds the 3-500 triode tubes which are connected in a grounded grid configuration. An ALC circuit
develops negative voltage that can be fed back to the transceiver to reduce its gain when the
amplifier is overdriven.The antenna transmit-receive (T/R) relay is normally actuated by relay
contacts, or an electronic switch, in the transceiver to place the amplifier in the transmit mode.
The relay contacts must be connected to ground. Operation problems will occur if the contacts
have more than zero volts DC.
LOCATION
Do not operate the Amplifier in excessively warm locations or near heating vents or radiators. Be
sure air can circulate freely around and through the Amplifier cabinet, and can provide an
unobstructed air inlet for the internal cooling fan. Do not place any books, magazines, manuals,
or equipment that will impede the free flow of air near the sides andthe hot air exhaust holes
located on the top of the cabinet.The internal fan allows an air flow of approximately 50 CFM. Do
not use an external auxiliary cooling fan with less than 50 CFM capacity.The exhaust air becomes
quite warm at high power levels. Do not position any heat-sensitive objects in the exhaust airflow
path.
AC LINE POWER CONSIDERATIONS
Before operating the amplifier, verify that the AC Voltage Power Block located inside the amplifier
has been wired correctly for the local AC supply you will be using. See the Voltage Power Block
Wiring Diagram for the correct wiring. Make sure the AC line cord has been disconnect and
filter capacitors have no charge on them before removing the top cover.
Verify that the rating of the line fuses located in the rear panel fuse holders is suitable for the AC
line voltage you will be using. The fuse should be the glass cartridge slo-blow type. The rating
should be either of the following:
120 VAC 20 Ampere
240 VAC 10 Ampere
Use only AC power outlets having a protective ground for connection to the amplifier. DO NOT
USE 2 conductor extension cords or 3 prong to 2 prong adapters that do not provide a protective
ground connection. Connection of the power cord to the power outlet must be made in
accordance with the following standard color code:
American European
Live Black Brown

9
Neutral White Blue
Ground (Earth) Green Green/Yellow
Use the following NEMA plug configurations according to the corresponding AC line voltage:
100/110 VAC 20 Ampere 5-15P
200/240 VAC 10 Ampere 6-15P or 6-20P
Due to the power involved, this Amplifier should have its own 240 VAC electric service line. This
line should have three 12-gauge conductors, and 10 ampere fuses in each "hot" wire. If a single
240 VAC line serves the entire station, make an effort to connect your equipment so the load is
balanced between the two "hot" wires.If you have only 120 VAC available, use a separate line
made up of 10 gauge conductors and 20 ampere fuses in each leg of the circuit. DO NOT use this
Amplifier at it full ratings on a regular house wiring circuit, as the ratings of the wire will almost
certainly be exceeded. Avoid excessively long runs of wire between your service entrance and
the Amplifier. A heavy flow of current in such a line results in a voltage drop which can affect the
performance of your equipment. The plug on the power cord of your Amplifier, if wired for 120
VAC operation, is for standard 120 VAC outlets (NEMA 5-15P). If the Amplifier is wired for 240
VAC operation, no plug is supplied with the line cord. Use a plug that matches your 240 VAC
receptacle (NEMA 6-15P or 6-20P). Your power connection must conform to section 210-21 (b)
of the National Electric Code, which reads, in part:
"Receptacles connected to circuits having different voltage, frequencies, or types of current (AC
or DC) on the same premises shall be of such circuits are not interchangeable."
When you install a new plug, make sure it is connected according to your local electrical code.
Keep in mind that the green line cord wire is connected to the Amplifier chassis.
ANTENNA
The output circuit of the Amplifier is designed to be connected to an unbalanced transmission line
that has a 50 ohm characteristic impedance. Lines of other characteristic impedance may be used
providing the SWR (standing-wave-ratio) does not exceed 2:1. In addition, the built-in wattmeter
is only accurate at 50 ohms.The RF OUT connector is a UHF type SO-239. You will need a
mating PL-259 plug for your transmission line.Use coaxial cables like RG-8U, RF-11U, or similar
types, for the transmission line. Due to the power level, the smaller types RG-58U, RG-8X, and
RG59/U are not recommended.The "A.R.R.L. Antenna Book" is readily available and includes
comprehensive reference work on transmission lines and antennas. Other similar handbooks for
the radio amateur are offered for sale and can often be found in a public library.
GROUNDING
Connect a good earth or water pipe ground to the ground post on the rear of the Amplifier. Use
the heaviest and shortest connection possible. Before you use a water pipe ground, inspect the
connections around your water meter and make sure that no plastic or rubber hose connections
are used. These connections interrupt the continuity to the water supply line. Install a jumper
around any insulating water connectors you may find. Use heavy copper wire and pipe clamps.
It is best to ground all equipment to one point at the operating position and then ground this point

10
as described above.
EQUIPMENT INTERCONNECTIONS
Interconnection between the Amplifier and a typical transceiver is shown in the "Interconnection
Diagram" located inside your tranceiver owners manual. Many brands of equipment usually follow
the same general pattern. Please refer to this diagram plus the amplifier's Rear Panel Pictorial
while reading the following:
RF IN Connect this socket to the RF output connector of your transceiver.
RF OUT Connect this socket to the cable coming from your antenna.
Note: Use shielded cable, such as audio-type cable, for the following connections.
KEY XMT Connect this socket to the Relay socket or keying contact on your transceiver. This
connector requires contacts that are normally open in the receive mode and closed in the transmit
mode. This contact sinks +12 VDC to ground at 80 mA.
+15 V XMT If your transceiver has a provision for +15 VDC on transmit for keying external
devices, such as linear amplifiers, connect this socket to the appropriate socket on your
transceiver. This provision requires factory activation at the time of shipment.
Note: If your transceiver has neither of the above keying methods, you will have to use some
other means. For instance, you could use a shorted RCA phono plug by placing it in the Key XMT
socket. Then, you would have to manually turn off and on the Operate/Standby switch located on
the front panel.
ALC OUTPUT Connect this socket to the ALC input of your transceiver. A 0 to 20 V negative ALC
voltage is present at this socket. Refer to your transceiver manual for proper connection
information. Whenever the Amplifier is overdriven, the ALC circuitry creates a negative voltage
that is fed back to the transceiver to reduce its gain and help prevent "flat-topping".Protective
circuitry of this nature is a valuable circuit element, but it is not a substitute for proper adjustment
of the transceiver drive.
SAFETY INTERLOCK SWITCH
While the Amplifier's top cover is in place, the interlock switch closes to allow AC line voltage to
reach the power transformer. When the top cover is removed, the interlock switch opens and
disconnects the line voltage. This does not discharge the bank of power supply filter capacitors.
Be sure to allow the filter capacitors to discharge before you touch anything inside the Amplifier.
You can select the High Voltage function of the Multimeter to check the high voltage potential.
DRIVING POWER
This Amplifier is designed to operate at full ratings when it is driven by a transceiver that has

11
approximately 100 watts of RF output. You can use a transceiver that has lower output power, but
the Amplifier's output will be less. If you use a transceiver that delivers more than 100 watts,
carefully adjust the driving power to avoid "overdrive" and the creation of spurious signals, which
create needless interference to other operators. IMPORTANT: In no case should you advance
the power output control of your transceiver beyond the point where the Amplifier's power output
indication ceases to increase. If you turn the control past this point , nonlinear operation may
occur.
TUBE
It is not abnormal for the tube to show a dull red color. But if the plate shows a bright orange or
yellow color, immediately investigate the tuning and drive conditions and make any necessary
corrections. After prolonged operation, let the Amplifier run for several minutes without drive
applied so the fan will cool the tubes before you turn the Amplifier off.
READING THE METERS
Refer to Front Panel Pictorial while you read the following information:
Multimeter: The Multimeter switch on the front panel of the Amplifier selects the right-hand
meter functions. Read the meter scale which corresponds to the setting of the Multimeter
switch as shown in Table A.
Grid Meter: The left-hand meter always indicates grid current between 0 and 300
milliamperes. Each Division indicates 10 milliamperes.
Table A
Multimeter Switch
Position Measures Scale Indication
Plate Voltage (PV) Plate Voltage Center scale indicates 0 to 3500 volts
(normal operating range is 2700 to 3200
volts) Each division represents 100 volts.
Plate Current (IP) Plate Current Top meter scale indicates 0 to 1400
milliamperes. Each division represents 40
milliamperes.
Power Output (PO) PEP RF Power Bottom meter scale indicates 0 to 2000
(PEP) voice peak only watts. Does not
measure average or RMS power
ALC ALC Detector Indicates relative ALC Output
TUNE-UP PROCEDURE

12
Please refer to the Front Panel Pictorial while reading the following.The current and voltage
figures given in this section are approximate. Actual indications will vary at each installation with
such factors as line voltage, transceiver drive, and load impedance. The following procedure for
tuning the Amplifier should only take a few seconds after you go through it a few times. Note the
Tune control position and the Load control position so you can preset it the next time you use a
particular band and frequency.For your convenience, the following chart shows typical settings:
TUNE-UP TABLE (50 Ohm Resistive Load with 240 VAC Line Voltage)
Freq
(Mhz) Band Drive Tune Control Load Control Plate Voltage Plate Current Grid Current Power Output
1.80 160
1.90 160
3.55 80
3.90 80
7.20 40
14.20 20
18.10 17
21.30 15
24.90 12
28.50 10
28.70 10
CW, RTTY, SSTV Procedure
Make sure you have the Amplifier connected as described in the Equipment Interconnections
Section. IMPORTANT: Before you proceed, make sure you have a dummy load or an appropriate
antenna is connected to the Amplifier RF Output connector.
1. Preset the Amplifier controls as follows:
On/Off Off
Operate/Standby Standby
Multimeter PV
ALC Adjust Minimum (Fully
counter clockwise)
2. Plug the line cord into a proper AC outlet.
3. Set the On/Off switch to On. The meter lamps should light and the fan should run. The red
power indicator LED should also be lite. The 0 to 3500 V scale on the Multimeter should indicate

13
approximately 2900 - 3200 volts.
4. Make sure your transceiver has been turned on and its drive level control has been set to
minimum.
5. Turn the Band Switch to the same band as you have selected on the transceiver. Then preset
the Tune Control and the Load Control to the positions indicated in the above chart for the band
you have selected.
6. With the transceiver drive still at minimum, set the Multimeter Switch to Plate Current (IP). The
0to 1400 ma scale should indicate zero. Now set the Operate/Standby switch to the Operate
position.
7. Key the transceiver (with no drive applied) and observe the plate current on the 0 to 1400 ma
scale. The plate current should read approximately 160 ma. more or less.
8. Apply only enough drive to obtain 50 ma of grid current and no more than 400 ma of plate
current. Now tune the Tune Control for maximum grid current. Unkey the transceiver. NOTE: It
is normal for the plate current to dip (be reduced) when you have maximum grid current. If the
grid current goes over 200 ma, immediately reduce the drive.
9. Again key your transceiver and observe the peak RF watts on your wattmeter. Adjust the Tune
Control and Load Control for maximum output on your wattmeter. This is accomplished by going
back and forth between each control.
10. Increase the transceiver drive until you obtain 250 ma of grid current. Now readjust the Tune
Control and Load Control for maximum output. The grid current should decrease.
11. Increase the transceiver drive for 200 ma of grid current. Then readjust the Tune Control and
Load Control for maximum output power. The output should now be around 1200 watts with 120
watts of transceiver drive power.
12. Apply only enough drive to indicate either 1200 watts of output power, or 160-200 ma of grid
current. Repeak the Tune Control and Load Control. Note: The grid current, plate current. and
output power must not exceed the following limits:
Grid current 220 ma
Plate current 800 ma
Output Power 1200 watts
13. When you operate in CW, reduce the drive power until the plate current is 700 ma or
less. Also when operating RTTY or SSTV, reduce the drive power until the plate current is
600 ma or less.
The Amplifier is now fully loaded for operation on CW, RTTY, or SSTV.
SSB Procedure

14
1. Tune up the Amplifier as described for CW operation.
2. Advance the transceiver drive and audio levels so that the modulation crest does not exceed
400 ma of plate current, 100 ma of grid current, or 1,500 watts of PEP output.
USING THE FRONT PANEL ALC CONTROL TO ADJUST AMPLIFIER
OUTPUT POWER.
You may want to utilize an alternative to adjusting the drive power at the transceiver. The Front
Panel ALC Adjustment Control allows you to adjust the ALC for the amount of output power you
desire. Using this procedure, you would set the ALC Control to minimum (fully counter-clockwise).
Tune the amplifier for maximum output. Then advance the ALC Control (clockwise) for the amount
of output power you want. The ALC circuit of the amplifier supplies negative feedback voltage
to the transceiver which reduces the amount of drive coming into the amplifier. Only use this
feature after your Amplifier has been properly tuned.
TUNED INPUT ADJUSTMENTS
Please refer to the Rear Panel Pictorial while reading the following.
Your Amplifier's tuned input circuits have been factory preset for the optimum match. However
before your initial operation, you may want to check the tuned input circuits for each band to see
if it has the proper match. A nominal match will show no more than 10 watts reflected with 100
watts of drive applied. NOTE: DUE TO THE LARGE BANDWIDTH ON 80 METERS, THE SWR
ON THE ABOVE 3.950 MHZ IS HIGH. YOU MAY HAVE TO USE YOUR TRANSCEIVER'S
ANTENNA TUNER FOR A BETTER MATCH.
To check the tuned input match, follow the following procedure:
1. Place a wattmeter in line between the transceiver and the Amplifier which reads reflected RF
power.
2. Select one of the HF bands on your transceiver, and then select the corresponding band on
the amplifier.
3. Place the amplifier in the Operate mode, and tune the amplifier according to the tune up
procedure.
4. Observe the reflect power between the transceiver and the amplifier. If it exceeds 5 watts,
adjust the corresponding mica trimmer capacitor located on the rear panel. This trimmer capacitor
is located through the corresponding rear panel access hole in the area marked Tuned Input
Adjustments. Use only a non-conductive flat blade adjustment tool.
5. Advance the mica trimmer capacitor's adjustment screw either clockwise or counter-clockwise
and observe the reflected power indication on the watt meter. Adjust for minimum reflected power.
6. Repeat this procedure for each band.

15
PERIODIC MAINTENANCE
Make sure the Amplifier has been disconnected for the AC power source and the high
voltage filter capacitors have bleed down to zero.
Remove the top cover from the Amplifier at least once a year and remove the dust. Dust
accumulationcan help cause the variable capacitors to arc between plates. Use the blower
connection on a vacuum cleaner or a soft bristle brush. Also, remove the tube from its socket and
check to see if any tarnish buildup has developed on the tube socket contacts. If so, use a Q Tip
and Tarn-X solution, and clean each of the socket contacts.
TROUBLESHOOTING CHART
Thefollowing charts lists specific difficulties that could occur in your Linear Amplifier. Several
possible causes may be listed for each difficulty. Refer to the Printed Circuit Board diagrams
(PCB) and the Schematic Diagrams to locate and identify the parts listed in this chart. If a
particular part is mentioned as a possible cause, check that part and other components
connected to it to see if they are defective. AS ALWAYS, BE SURE THE AMPLIFIER POWER
CORD HAS BEEN REMOVED FROM THE AC LINE RECEPTACLE AND THE HIGH VOLTAGE
FILTER CAPACITORS HAVE BLED DOWN TO ZERO VOLTS BEFORE REMOVING THE TOP
COVER FOR YOUR INSPECTION.
TROUBLESHOOTING CHART
DIFFICULTY POSSIBLE CAUSE
No AC power 1. Fuse F1 or F2 rear panel
2. Jumpers missing on Terminal Block TB1
3. Transformer T1
4. On/Off Switch SW2A or SW2B
5. Interlock Safety Switch SW1
6. Step Start Relay K1 or related circuitry
Multimeter inoperative in High Voltage
Function 1. Resistors R301, R302, R303, R304, High Voltage PCB-110
2. Multimeter Switch SW401A or SW401B
Meter Switch PCB-510
3. M-2 Multimeter
Multimeter inoperative in Plate Current
Function 1. Resistors R308 - R310 LV & Bias PCB-260 2. Switch SW401A&B Meter Switch PCB-510
3. M-2 Multimeter

16
Multimeter inoperative in Power Output
Function 1. Components on ALC/Power PCB-610 a. Capacitors C601 -C603, C604, C608,
C609
b. Diodes D601, D602
c. Resistors R601, R605, R606
d. POT R605
e. Transistor Q601
2. Switch SW401A&B Meter Switch PCB-510
3. M-2 Multimeter
4. +12V Regulated Power Supply on LV & Bias
PCB-260
Multimeter inoperative in ALC Function 1. Components on ALC/Power PCB-610
a. Capacitors C606 & C607
b. Resistors R602 & R603
c. Diodes D603 & D604
2. POT R13 on front panel
3. Resistor R312 LV & Bias PCB-260
4. Switch SW401A&B Meter Switch PCB-510
5. M-2 Multimeter
Plate idle current over 160 ma or does not read
zero in standby mode 1. Components on LV & Bias PCB-260 a. Transistor Q302
b. Diodes D303 - D310
c. Resistor R304
d. Transient Voltage Suppressor TSD301
e. Capacitor C302
f. Resistors R308 - R310
No Plate idle current 1. Components on LV & Bias PCB-260
a. Transistor Q302
b. Diodes D303 - D310, D311
c. Resistor R301 &R304
d. Transient Voltage Suppressor TSD301
e. Capacitor C302
f. Resistors R308 - R310
g. Relay K301A
No Plate Voltage or only 50% Plate Voltage 1. Components on HV Capacitor PCB-105
a. Capacitors C201 - C208
b. Resistors R201 - R208
2. Components on HV Diode PCB-110
a. Diodes D101 - D110
b. Capacitors C101 - C110
c. Resistor R209

17
No Plate Idling current cut-off when amplifier is
not keyed or is in standby mode 1. Components on LV & Bias PCB-260 a. Transistor Q302
b. Diodes D303 - D310, D311
c. Resistor R301 &R304
d. Transient Voltage Suppressor TSD301
e. Capacitor C302
f. Resistors R307 - R310
g. Relay K301A
h. Zener Diode ZD301
2. Components on HV Diode PCB-110
a. Resistors R301 - R304
Meter Lamps do not light 1. Components on LV & Bias PCB-260
a. Fuse F302
b. Bridge Rectifier D311
c. Capacitors C303 - C305
d. +12v Regulator Q303
2. Associated +12v Supply wiring
3. Meter Lamps PL1 - PL4 Meter Switch PCB-
510
No Grid Current Meter Indication with Plate
Current Indication OK 1. Components on LV & Bias PCB-260 a. Resistor R311
b. Capacitor C306
2. Grid Meter M-1
Amplifier will not key when transceiver is keyed
to transmit 1. Components on LV & Bias PCB-260 a. Fuse F301
b. Bridge Rectifier D302
c. Capacitor C301
2. Components on RF I/O Switching PCB-350
3. Operate Standby SW4 Front Panel
Amplifier will not key when transceiver is keyed
to transmit 1. Components on LV & Bias PCB-260 a. Fuse F301
b. Bridge Rectifier D302
c. Capacitor C301
2. Components on RF I/O Switching PCB-350
3. Operate/Standby SW4 Front Panel
ALC Inoperative 1. Improper connection between transceiver
and amplifier
2. POT R13 (ALC Adjust) on front panel

18
No RF Output 1. Improper connections between transceiver,
amplifier, and antenna
2. Transceiver and amplifier are set to different
bands
3. Improper Tuned Input adjustment
4. Defective RF I/O Switching PCB-350
5. Defective RF Output T/R Relay RY1
6. Defective Band Switch SW3A, SW3B
7. Defective Tuned Input Band Switch SW3C
Tuned Input can not be adjusted for proper
match 1. Defective Component Tuned Input PCB-450 2. Defective Tuned Input Band Switch SW3C
3. Components on LV & Bias PCB-260
a. Fuse F302
b. Bridge Rectifier D311
c. Capacitors C303 - C305
d. +12v Regulator Q303
4. Associated +12v Supply wiring
5. Transceiver and amplifier are set to different
bands
6. Improper connections between transceiver,
amplifier, and antenna
Red Power LED not functioning 1. +12 VDC supply located on LV & Bias PCB-
260 and related wiring
2. LED D1 defective
Green Transmit LED not 1. +12 VDC supply located on LV & Bias PCB-
260 and related wiring
2. LED D2 defective
3. Relay K301 and related keying circuitry
CIRCUIT DESCRIPTIONS
Refer to the Appropriate Schematic Diagrams and PCB Layouts while you read the following
paragraphs.
POWER SUPPLY
Power transformer T1 supplies the power required to operate the Linear Amplifier. A dual-winding
primary allows the amplifier to be operated from120 VAC or 240VAC. These winding are
connected in parallel for 120 VAC operation or in series for 240 VAC operation. Two 10 ampere
or two 20 ampere fuses protect the transformer against overload depending on the primary
voltage. Capacitors C11 & C12 provide AC line bypassing.This amplifier uses a special
combination safety interlock/step-start circuit. Interlock switch SW1, On/OFF power switch
SW2A&B must be closed before power is supplied to the primary of transformer T1. Relay K-1

19
provides a step-start when the amplifier is switched on. Components C12, R10, D10 provide the
time delay to minimize the inrush current. Resistors R11 & R12 limit the inrush current while the
delay circuit cycles. After a 1 to 2 second delay the contacts on relay K-1 close allowing the full
current to be applied to the primary of T-1.Terminal Block TB1 allows for the selection of the line
voltage to be used. See the Terminal Block Wiring Diagram for the correct wiring. Cooling Fan
B1 is provided 100/120 VAC by connection across only one of the primary windings at TB1. B1
always operates on 100/120 VAC regardless of which AC line voltage is used.The secondary
windings of T1 provides the following secondary voltages: 5.6 VAC tube filament, 12.0VAC +12
VDC Power Supply, 110 VAC RF I/O Switching Supply, 1200 VAC Plate Voltage Supply
PLATE VOLTAGE
The 1200 VAC output of T1 is connected to a full-wave voltage doubler circuit consisting of the
components on HV Capacitor PCB-105 and HV Diode PCB-110. Diodes D101 - D110 rectify the
secondary AC voltage and capacitors C201 - C208 filter this voltage. Capacitors C101 - C110 are
connected across the diodes to protect them against transients. Resistors R201 - R208 are
connected across the filter capacitors to equalize the voltage drop across each capacitor. These
resistors also act as bleeder resistors for the filter capacitors to discharge them when the amplifier
is turned off. One of the red 1200 VAC secondary lead is connected to the junction of C204 &
C205, and the other red 1200 VAC secondary lead is connected to the junction of D105 & D106.
During the AC line cycle when the lead at C204 & C205 junction is positive, diodes D101 - D105
conduct and capacitors C201 - C204 are charged. During the other half of the AC line cycle, the
red lead connected to the junction of D105 & D106 becomes positive. Capacitors C205 - C208
charge and Diodes D106 - D110 conduct. The two capacitor strings are in series across the load,
and the voltages of each capacitor group add together. The capacitor bank charges to twice the
peak voltage of the 1200 VAC secondary voltage (1200 VAC x 1.414 x 2 =3,393 VDC).Resistor
R209 is a protection resistor connected in series with the Plate Voltage Circuit. If a short
develops, this resistor prevents the B- from rising to the B+ potential. Thus providing protection
for all the components within the B+ circuit including the 3-500 triode. Resistors R301 - R304 are
discussed under Metering Circuits.
TUBE FILAMENT AND BIAS
The 5.2 VAC secondary windings on T1 secondary supplies 15 amperes for the amplifier's tube
filament. The filament voltage is fed to tube V1 through RFC2 which is a bifilar wound coil on a
ferrite rod core. This coil forms a choke to raise the tube filaments above RF ground potential so
that the driving voltage is not short circuited. Capacitors C59 & C60 keep RF out of the filament
supply circuit. In the transmit mode, the center tap of the filament winding (5.2 VAC) is connected
to ground through the bias circuit located on the LV & Bias PCB-260. This circuit consists of bias
transistorQ302, transient suppressor TSD301, bias resistor 301, bypass capacitor C302,
resistors R304 & R311, relay K301A, diodes D303 - D310. This bias circuit develops +11 VDC
operating bias for tube V1 and limits the idling plate current. In Standby (receive) Mode, a +24
VDC voltage is formed across resistor R307. This voltage is applied to the tube filaments, in
addition to the AC voltage, to bias the tube beyond cut off so that no plate current flows.
12 VAC SUPPLY

20
The 12 VAC secondary winding of T1 supplies the voltage for the +12 VDC supply circuit located
on the LV & Bias PCB-260.
110 VAC ISOLATION SUPPLY
The 110 VAC secondary winding of T1 provides an isolated supply voltage for the +110 VDC
power supply located on the LV & Bias PCB-260.
RF INPUT CIRCUITS
When the amplifier is in the Stanby Mode (receive), Relay RY1 and Relay RY2 (located on the
RF I/O Switching PCB) are in their normally open state. Thus, RF energy supplied from the
transceiver passes through RF Input Connector (J2), RY2, RY1, and RF Output Connector (J1)
to the antenna. The amplifier has been bypassed. Capacitors C70 & C71 tune the mismatch that
occurs with the relay contacts located inside RY1 & RY2.When the amplifier has been keyed
(Transmit Mode). RY2 closes and the RF energy supplied by the transceiver passes though
RY2's closed contacts to the Tuned Input PCB-450. The signal then passes through the selected
input matching network and then on to coupling capacitors C57 & C58 located at the tube
filaments.
TUBE
The amplifier's tubes are connected in a class AB2 grounded grid circuit. RF driving power is
applied to the filaments in the normal cathode driven configuration. As mentioned in the Filament
&Bias Section, RFC2 holds the filaments above RF ground.Pins 2, 3, and 4 of the tube are
internally connected together and are connected to ground.Parasitic chokes PC1 & PC2 are
connected to the plate lead to suppress any VHF parasitic oscillations. The positive side of the
power supply (B+) is connected to the tube's plate through RFC3 (Plate Choke). Capacitor C56
provides a low impedance path to ground for any RF energy that my get through RFC3.
Capacitors C54 & C55 are DC blocking capacitors. They allow the RF signal to enter the output
tank circuit, and they block the DC high voltage from entering the tank circuit.Fan B1 circulates
cooling air around the tubes.
RF OUTPUT CIRCUITS
The tuned output circuit of the Amplifier is a pi network in conjunction with a 4:1 transformer(L3).
The pi circuit transforms the plate load impedance down to 200 ohms. The 4:1 transformer further
transforms the 200 ohms down to 50 ohms. L3 has a secondary function to provide a broadband
L coil for harmonic suppression.Band Switch SW3A progressively shorts out the unused portions
of tank coils L1 & L2. The tank coil turns in use are tuned to resonance by Tune Capacitor C5.
Load Capacitor C50 is tuned to complete the impedance match between the tube and the 4:1
transformer L3. Transformer L3 is then connected to RF Output connector J1 through T/R relay
RY1. Capacitor C52 provides additional capacitance for C51 on 80 & 160 meters. Capacitor C53
provides additional capacitance for C51 on 160 meters. If DC plate voltage should enter the tank
circuit due to a short in either DC Blocking Capacitors C54 & C55, the DC voltage has a path to
ground through the 4:1 Xfmr (L3). This will short-circuit the high voltage supply which will blow
the AC line fuses. Also, DC plate will be prevented from entering the Antenna.