QRO Technologies HF-2500DX User manual

QRO HF-2500DX LINEAR AMPLIFIERQRO HF-2500DX LINEAR AMPLIFIER
INSTRUCTION MANUAL
QRO TECHNOLOGIES, INCQRO 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: October 1996
COPYRIGHT 1996 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: 50 to 60 watts nominal for rated output
Maximum Output Power: 1,500 watts peak all modes including SSB, CW, and con-
tinious carrier or modulated carrier. Carrier operation (RTTY,
FM, or SSTV) for more than 30 minutes requires use of
auxiliary cooling,
Power Gain: Nominally 14 db
Automatic Limiting
Control (ALC):0 to -20 Volts negative going, adjustable from Front Panel
Harmonic Suppression: Meets F.C.C. Requirements
Keying: Requires relay contact closure or sink of 80 ma @ 100 VDC
or +15 VDC on transmit supplied by transceiver
Input Impedance: 50 ohms unbalanced, VSWR <1.5:1
Output Impedance: 50 ohms unbalanced with SWR 2:1 or less
Tube Requirement (2): Svetlana GU74b (4CX800A) (2) Tetrodes
Power Line Requirement: 200/240 VAC, 50/60 Hz at 25 amperes maximum
Front Panel: Multimeter (Plate Voltage, Plate Current, Screen Voltage)
(See Front Panel Pictorial) Screen 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
Fan High/Fan Low Switch
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)
Ground Post
Fuses (two 20 ampere for 100/120 VAC)
Dimensions: 20"W X 19"D X 8"H
Net Weight: 90 lbs. (48 kgs.)

3
TABLE OF CONTENTS
Warranty 4
Proprietary Notice 4
Safety Notification 5
Unpacking & Inspection 6
Reshipment Instructions 6
Top Cover Removal 6
Transformer & Tube Installation 6, 7
Line Voltage Selection Power Block Wiring 7
Introduction 7, 8
Location 8
AC Power Line Considerations 8, 9
Antenna 9
Grounding 9
Equipment Interconnections 9, 10
Safety Interlock Switch 10
Driving Power 10
Tube Precaution 10
Reading the Meters 10, 11
Front Panel Switches & Controls 11, 12
Initial Power Up 12
Tune-Up Procedure 12, 13, 14
Using the ALC Adjust Control 14
Periodic Maintenance 14, 15
Troubleshooting Chart 15, 16, 17
Circuit Descriptions 17, 18, 19 20, 21, 22
Addendum #1 Power Block Wiring
Addendum #2 Schematics
Addendum #3 PCB Layouts
Addebdum #4 Front & Rear Panel
Pictorials

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WARRANTY
_____________________________________
The HF-2500DX 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
GU-74B (4CX800A) tetrodes which carry a separate one year warranty. 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, printed circuit board layouts, 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
fromQRO Technologies, Inc. This amplifier is covered by copyrights both in the
United States of America and throughout the world.

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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, plate transformer, tubes/control transformer.
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.
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
during return shipment.
TOP COVER REMOVAL
Remove the Amplifier's top cover by removing the ten 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 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 , plate transformer, and filament transformer each shipped
in a separate cartons. As part of the installation process, you must install the tubes and
transformers.
Filament & Control Transformer: Remove the filament & control transformer (smallest
transformer) from its shipping carton. You will notice one indexed connector on the ends of the
transformer leads. Place this transformer in the rear of the power supply compartment next to the
blower. Position the transformer so the transformer leads and indexed connector is on the right
side when viewed from the front of the amplifier. The four mounting holes on the chassis should
align with the transformer mounting feet. Use at least three of the four 1/4-20 x 5/8 screws and
nuts to secure the transformer. One mounting foot is difficult to reach, and it is not absolutely
necessary to secure it. Locate the amplifier's matching index connector. Connect the two
matching connectors. There is only one way the two connectors can go together. When the two
connectors are locked together, you should hear a snap sound.
PLATE TRANSFORMER: Remove the plate transformer (large transformer) from its shipping
carton. You will notice two indexed connectors. Position the transformer so the connector with the
red leads is on the left and the connector with the black and white leads is on the right side when

7
viewed from the front of the amplifier. Carefully place the plate transformer into the power supply
compartment cavity between the blower and the circuit board stack located behind the front panel
meters. Align the transformer with the chassis mounting holes and secure it to the chassis with
at least three 1/4-20 x 5/8 mounting screws and nuts. The fourth hole is rather difficult to access,
and it is not absolutely necessary to secure it. Locate the two amplifier's matching index
connectors. Connect the two matching connectors. There is only one way the two connectors can
go together. When the two connectors are locked together, you should hear a snap sound.
TUBES: The tube sockets are located on the left side of the amplifier. They each have seven
contacts which match the seven pins on the 4CX800A tetrodes. Remove the tubes form their
shippingcartons, and insert each tube into the socket making sure that the pins align with the
socket contacts. The tubes should seat without too much pressure applied. If you have to use a
lot of pressure, you most likely have the wrong pin alignment. If the tube pins and socket contacts
are not aligned, the amplifier will not function properly and damage to the tube may result. Once
the tubes have been properly seated in their sockets, slip the two anode connectors over the tube
anodes.
LINE VOLTAGE SELECTION POWER BLOCK WIRING
Your amplifier has been factory wired for 220 - 240 VAC 50/60 Hz. operation. If you need to
change the line voltage configuration, refer to the two Power Block Wiring Diagrams while reading
this section. Locate the Line Voltage Power Block. It is located inside the amplifier just behind the
filament & control transformer. It contains 5 screw connection terminals. It also has black and
white leads connected to it.
Convert 240 VAC to 200 VAC: One wire jumper (J1) is connected to terminals 3 & 4. Remove
the J1 connection to terminal 3 and connect it to terminal 2. Remove the small back wire
connected to the right side of terminal 3, and connect it to right side of terminal 2. Remove the
large white wire connected to the left side of terminal 6 and connect it to the left side of terminal
5. 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 ten 6-32 x 3/8 mounting screws and washers.
Partially tighten each screw. When all ten screws have been 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 tubes.
INTRODUCTION
The QRO Model HF-2500DX Linear Amplifier is a completely self-contained, grounded cathode
grid driven, linear amplifier. It is designed to operate at 1,500 watts peak all modes including SSB,
CW, and continuous or modulated carrier (e.g., RTTY, FM, SSTV). Continuous or modulated
carrier operation for more than 30 minutes at or near maximum rated output power
requires use of auxiliary cooling. The HF-2500DX is designed to be used with any transceiver

8
which can deliver adjustable output power from 0 to 100 watts. A grid driven input circuit using
a50 ohm 100 watt non-inductive shunt resistor feeds each 4CX800A tetrode tube which are
connected in a grounded cathode 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. A +15 VDC contact is provided for transceivers utilizing a + 15 VDC on transmit for T/R
switching.
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 and the 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 disconnected 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 20 - 25 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
Neutral White Blue
Ground (Earth) Green Green/Yellow
Use the following NEMA plug configuration: 200/240 VAC 20 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 20 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. DO NOT use this Amplifier at it full ratings on a regular

9
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
aline results in a voltage drop which can affect the performance of your equipment. 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.
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 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
as described above.
EQUIPMENT INTERCONNECTIONS
Interconnection between the Amplifier and a typical transceiver is shown in the "Interconnection
Diagram" located inside your transceiver 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.

10
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 T/R relay socket 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.
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
approximately 50 watts of RF output. If you use a transceiver that delivers more than 50 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 ceases to increase. If you turn the control
past this point , nonlinear operation may occur.
TUBE PRECAUTION
After prolonged operation, let the Amplifier run for several minutes without drive applied so the

11
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 directly below the two panel
meters selects the right-hand meter functions. Read the meter scale which corresponds to the
setting of the Multimeter switch as shown in Table A.
Table A
Multimeter Switch
Position Measures Scale Indication
Plate Voltage (PV) Plate Voltage Bottom scale indicates 0 to 3.5 KV
(normal operating range is 2.4 KV to 2.6
KV volts) Each division represents .1 KV
(100 volts).
Screen Voltage (SV) Screen Voltage Bottom scale indicates 0 to 3.5 KV
(normal operating range is .35KV (350
volts) Each division represents .1 KV (100
volts).
Plate Current (IP) Plate Current Top meter scale indicates 0 to 2.8
amperes. Each division represents .8
amperes (800 milliamperes).
Screen Grid Meter: The left-hand meter always indicates screen grid current between 0 and 150
milliamperes. Each Division indicates 5 milliamperes.
FRONT PANEL SWITCHES & CONTROLS
On/Off Switch: Rocker type switch which turn the amplifier on or off
Operate/Standby Switch: Rocker type switch used to place the amplifier in a transmit mode
Fan High/Low Switch: Rocker type switch which control blower speed
ALC Control: Varies the negative feedback voltage to your transceiver. A clockwise rotation
increases this voltage which reduces the drive power delivered to the amplifier from the
transceiver. The ALC line between the transceiver and the amplifier must be properly connected
for this feature to operate.

12
Fault Light/Switch: If you amplifier is operated in such a manner to produce excessive screen
grid current, a protection circuit will place the amplifier in a standby mode. A red light will light in
the fault switch. The amplifier can be reset into a transmit mode by pushing the red switch. A
successful reset will be indicated when the fault light turns off.
Tune Control: A 6-1 vernier drive control used to adjust the input capacitor of the pi output tank
circuit during tune up. 0 - 100 logging scales provide a means to record your tune up settings for
future reference.
Load Control: A 6-1 vernier drive control used to adjust the output capacitor of the pi output tank
circuit during tune up. 0 - 100 logging scales provide a means to record your tune up settings for
future reference.
Band Selector Switch: Selects the desired band of operation
Red LED: When lit, the amplifier has been turned on, and it has gone through its warm up cycle.
Green LED: When lit, the amplifier has been keyed and amplifying the power supplied by the
transceiver.
INITIAL POWER UP
Preset the amplifier's front panel controls as follows:
On/Off Off
Operate/Standby Standby
Multimeter PV (Plate Voltage)
Fan Fan High
ALC Adjust Full counter clockwise
Tune Control Zero
Load Control Zero
Band 160
Turn the amplifier on by placing the On/Off switch in the on position. The meter lights and blower
should immediately come on. The amplifier is now in its two minute warm up cycle. During this
warmup period, check for the following readings:
Screen (Screen Current): Zero
PV (Plate Voltage): 2.4 KV to 2.6 KV
SV (Screen Voltage): Approx. .35 KV (350 V)
IP (Plate Current): Zero
OBSERVE THE PLATE CURRENT (IP) DURING THE WARM-UP PERIOD. IF IT STARTS TO
RISE, IMMEDIATELY TURN THE AMPLIFIER OFF. THE PLATE CURRENT SHOLD NOT RISE
DURING THE WARM-UP PERIOD. CALL QRO TECHNOLOGIES FOR INSTRUCTIONS. Place
your transceiver in the CW mode or any mode that will provide a continuous carrier for tuneup.
At this time make sure that your transceivers output power level has been set to zero.

13
TUNE UP PROCEDURE
Before making any tune up procedures, make sure your amplifier is connected to an
appropriate load capable of handing at least 1,500 watts of power. Failure to do so may
result is serious damage to your amplifier.
When the two minute warmup cycle has been completed, the red power light will turn on. The
amplifier is now ready for tune up. At this point, place your transceiver in the SSB mode with the
mic gain at minimum. Put the amplifier's Operate/Standby switch in the operate position. Key your
transceiver and you should notice the green transmit LED on the amplifier lite. You should also
hear the amplifier's internal relays latch. With the transceiver keyed and the amplifier's Multimeter
switch in the IP position, observe the plate current (IP). It should be in the neighborhood of
.400 - .500 amperes more or less. Also, your screen current should indicate a negative reading.
In other words, it will move to the left. This is normal. Unkey your transceiver, and place the
amplifier in the standby mode.
TUNEUP OBJECTIVE: The objective of the tuneup procedure is to bring the amplifier to
resonance by adjusting the tune & load controls for the proper level of screen current. You will
adjust tune control so the screen current peaks on the screen current scale. You will also adjust
theload control to bring the screen to the proper level. When tuning on 160 meters and 80
meters, you may notice the screen current drift downwards. This is a result of the padder
capacitors on the load side warming and changing their values. We are not concerned about an
absolute steady state of screen current. We simply want you to get the screen current to peak on
scale and adjust the load control for the specified level of screen current (50 mA). When re-keying
after tuneup, the screen current may initially exceed 50 mA. This is OK because the screen
current will reduce to 50 mA. The amplifier will go into the fault state if the screen current goes
to a dangerous level.
1. Place your transceiver in CW mode, and set its output power level to 30 wattts for 160, 80, 40
meters and 20 watts for 20, 15, 10 meters.
.
2. Place the amplifier in the operate position. Make sure the Tune & Load controls are set at zero.
3. Key your transceiver, and you should notice the screen current meter move to the left indicating
negative current. Again, this is normal. Advance the loading control clockwise until you see a
slight rise in screen current. If you do not see this rise, adjust the tune control clockwise to
the 50 position and then adjust the load control for a reading of 10 or 20 mA. You may see
the screen current dip to the left. Keep advancing the load control clockwise, and the
screen current will continue to rise.
4. Turn the tune control clockwise until the screen current reads 50 - 100 mA. If the screen
current goes full scale, turn the tuning control counterclockwise until the screen current meter
reads between 50 - 100 mA. If the screen current should rise to a dangerous level, the amplifier's
protection circuit will place the amplifier into a fault state, and the red fault button light will come
on. If this occurs, readjust the tune control counterclockwise, and push the fault light button to
reset the amplifier, and start again.

14
5. Turn the load control counterclockwise, and the screen current should start to fall. Continue
to turn the load control counterclockwise until the screen current reads 25 mA.
6. Turn the tune control clockwise until the screen current reads between 50 - 100 mA. Again, turn
the load control counterclockwise until the screen current reads 25 mA. Keep repeating this
procedure until you see the screen current's maximum peak occurs somewhere on the
screen current scale. Then, adjust the loading control counterclockwise (reduce) or
clockwise (increase) until the screen current reads approximately 50 mA.You are now tuned
to resonance for the input power applied. Again, on 160 meters and 80 meters the screen current
may drift downward the longer you keep the amplifier keyed. We are not concerned about an
absolute steady state of screen current on these bands. Simply adjust the tune control for a on
scale screen current peak, and adjust the load control for a 50 mA reading.
7. Increase your dive power in 20 watt increments. With each increment repeat the procedure in
item six until you have your desired level of power output.
REMEMBER THIS AMPLIFIER DOES NOT REQUIRE MUCH DRIVE POWER. SO
START WITH LOW DRIVE POWER, AND THEN TUNE TO RESONANCE AS
OUTLINED ABOVE. OTHERWISE, ARCING MAY OCCUR INSIDE YOUR
AMPLIFIER.
NEVER RUN YOUR AMPLIFIER FOR ANY SUSTAINED PERIOD WITH A
SCREEN CURRENT READING GREATER THAN 50 MILLIAMPERES. IF YOU
DO, DAMAGE AND FAILURE OF THE 4CX800A TETRODES WILL RESULT, AND
THEY WILL NOT BE COVERED BY SVETLANA'S WARRANTY!
To facilitate your initial tune up, we have included a tune up chart. These settings and readings
are into a 50 ohm dummy load. Your actual reading may vary do to any reactance in your
antenna. Record your settings for future reference. You can control the power level of your voice
peaks on SSB by advancing the ALC Control clockwise assuming you have the ALC line
connected between your transceiver and amplifier.
TUNE-UP TABLE (50 Ohm Resistive Load) with 10 ohms
of Cathode resistance.
Frequency
(MHZ) Power Input Tune Load Power Output Screen Current (IP) Plate Current
1.80
1.90
3.60
3.90
7.20
14.20

15
18.10*
21.30
24.90*
28.50
*Transceiver's Tuner Used
AWord About Wattmeters: The most reliable and accurate Wattmeters are either the Bird or
Coaxial Dynamics thru feed. Wattmeters which use a ferrite core for r.f. sampling can be
unreliable at high power levels. If you are using such a wattmeter and you observe an output level
less than 1,500 watts for the values listed above, your wattmeter is probably not giving you an
accurate reading.
Input SWR: The input SWR for 160 & 80 meters will be less than 1.5 :1. The input SWR for 40
meters should be around 1.5 :1 to 1.6 :1. Input SWR for, 20, 15, and 10 meters is at the most
1.5:1. These input SWR conditions should present no problem due to the lower drive power
requirements of this amplifiier. If you prefer a lower input SWR, use your transceiver's tuner to
adjust for a better match.
WARC Band Operation: The HF-2500DX will operate on the WARC bands. You may need to
use the transceivers internal tuner to provide a low input SWR on these bands. Use the following
band positions: 17 Meters use 15 Meter position, 12 Meters use 10 Meter position. Once you
have a low SWR reading using your transceiver's tuner, proceed with the tune up procedure
outlined above.
SSB OPERATION: Some transceivers RF output (carrier level) control DOES NOT control
the output power during SSB operation. If you have one of these transceivers and you go
to SSB operation after initial the initial tune up procedure, your voice peaks may cause
the screen grid current to go past full scale causing the amplifier to go into the fault state.
You will have adjust your microphone gain or speech processor so the screen current and
power output levels are within the specified levels. The ALC control can facilitate this
procedure. It is normal to see some negative indication of screen current during SSB
operation.
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

16
feature after your Amplifier has been properly tuned.
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 tubes from their sockets
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.
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. Solid State Relays SR! or SR2 or related
circuitry
Multimeter inoperative in High Voltage
Function 1. Resistors R210, R211, R212, R213 High Voltage Diode PCB
2. Multimeter Switch SW501A or SW01B Meter
Switch PCB
3. M-1 Multimeter
4. Transformer T-1 Secondary
5. Component failure on HV Diode or HV
Capacitor PCB

17
Multimeter inoperative in Plate Current
Function 1. Resistors R311 LV & Bias PCB 2. Switch SW401A&B Meter Switch PCB
3. M-1 Multimeter
4. F303 2 Ampere Fuse
Multimeter inoperative in Screen Voltage
Function 1. Components on Screen Supply PCB a. Capacitors C401 or C402
b. Diodes D401, D402
c. Resistors R405, R406, R407, R408
d. Zener Diodes ZD401 - ZD404
e. Fuse F401 2 Ampere Fuse
2. Switch SW401A&B Meter Switch PCB-510
3. M-1 Multimeter
4. Transformer T-1 Secondary
Plate idle current over 800 mA 1. Components on LV & Bias PCB
a. Zener Diodes ZD301
b. Relay K4
Plate Current does not read zero in standby
mode 1. Components on LV & Bias PCB a. D307 Bridge Rectifier
b. C311 Electrolytic Capacitor
c. Relay K4
d. Fuse F301 2 ampere
No Plate idle current 1. Components on LV & Bias PCB
a. Fuse 303 2 Ampere
b. Shunt Resistor R311
2. Screen Supply PCB component failure
Meter Lamps do not light 1. Components on LV & Bias PCB
a. Fuse F302
b. Bridge Rectifier D306
c. Capacitors C307, C308, C309
d. +12v Regulator U2
2. Associated +12v Supply wiring
3. Meter Lamps PL1 - PL4 Meter Switch
Amplifier will not key when transceiver is keyed
to transmit 1. Components on LV & Bias PCB 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

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Amplifier will not key when transceiver is keyed
to transmit 1. Components on LV & Bias PCB-260 a. Fuse F301
b. Bridge Rectifier D301
c. Capacitor C301
2. Resistors R305, R306
3. Operate/Standby SW4 Front Panel
4. Components on RF I/O Switch PCB
a. R601, R603, R604, R606, R607
b. Relay RY1
c. C601, C602
d. D601, D602, D603
e. Q601
ALC Inoperative 1. Improper connection between transceiver
and amplifier
2. POT R13 (ALC Adjust) on front panel
3. Components on RF I/O Switch PCB
a. C608, C609, C610
b. R608
c. D604, D605
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
5. Defective RF Output T/R Relay RY1
6. Defective Band Switch SW3A, SW3B
7. Defective Input Band Switch SW3A
Grid Trip Circuit Inoperative 1. Defective Trip Reset Switch SW6
2. Components on LV & Bias PCB
a. R305
b. Relay K1
c. Relay K5
d. R310, C317, C318, D310, D311, Q2
Red Power LED not functioning 1. +12 VDC supply located on LV & Bias PCB
related wiring
2. LED D1 defective
3. Relay K3
Green Transmit LED not functioning 1. +12 VDC supply located on LV & Bias PCB
related wiring
2. LED D2 defective
3. Relay K2 and related keying circuitry

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Two minute warmup cycle not functioning Components on LV & Bias PCB
1. U3 555 Timer and related components
2. Transistor Q1
3. K3 Relay
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 from 200 VAC or 240 VAC. Two 20 ampere fuses
protect the transformer against overload. Capacitors C10 & C11 provide AC line bypassing. This
amplifier uses a special combination safety interlock/solid state relay circuit. Interlock switch
SW1, On/OFF power switch SW2A&B must be closed before power is supplied to the primary of
transformer T1. Solid State Relays SR1 & SR2 provides a soft start when the amplifier is switched
on. They only turn on when the AC line voltage crosses the zero degree point of the sine wave
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. Switch SW4 in combination with resistors R307A & R307B
provide a high or low setting for the fan. The secondary windings of T1 provides the following
secondary voltages: 1,900 VAC Plate Voltage Supply & 200 VAC Screen Voltage Supply.
PLATE VOLTAGE
The1900 VAC output of T1 is connected to a full-wave bridge rectifier circuit consisting of the
components on HV Capacitor PCB and HV Diode PCB. Diodes D101 - D120 rectify the
secondary AC voltage and capacitors C200 - C207 filter this voltage. Capacitors C101 - C120 are
connected across the diodes to protect them against transients. Resistors R200 - R207 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 1900 VAC secondary leads is connected to the junction of D101
&D106, and the other red 1900 VAC secondary lead is connected to the junction of D111 & D116.
During the AC line cycle when the lead at D101 & D106 junction is positive, diodes D101 - D105
& D111 - D115 conduct and capacitors C200 - C207 are charged. During the other half of the AC
line cycle, the red lead connected to the junction of D111 & D116 becomes positive. Capacitors
C200 - C207 charge and Diodes D106 - D110 & DD116 - D120 conduct. The capacitor bank
charges to the peak voltage of the 1900 RMS VAC secondary voltage (1900 VAC x 1.414
=2,686.60 VDC).

20
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 4CX800A tetrodes. Resistors R110 -
R113 & R212 - R215 are discussed under Metering Circuits.
TUBE FILAMENTS
The 12.6 VAC secondary windings on T2 secondary supplies 8 amperes for the amplifier's tube
filaments. The 4CX800A tetrodes are indirectly heated cathodes, and the tube filaments must
heat them for an initial two minute warmup period.
12 VAC SUPPLY
The 12 VAC secondary winding of T2 supplies the voltage for the +12 VDC supply circuit located
on the LV & Bias PCB. +24 VDC is also produced on the LV & Bias PCB using a voltage doubler
circuit using this 12 VAC supplied by T2.
120 VAC ISOLATION SUPPLY
The 120 VAC secondary winding of T2 provides an isolated supply voltage for the +120 VDC
power supply located on the LV & Bias PCB. This supply uses a bridge rectifier diode to rectify
the voltage along with a filter capacitor. The +120 VDC power supply provides the voltages for
the internal T/R switching plus the tube grid bias.
CONTROL GRID BIAS
A cutoff bias voltage of -160 V is supplied by circuit consisting of bridge rectifier D307, capacitor
C311. The transmit -70V bias is supply by these components along with zener diodes ZD301,
resistor R304 when relay K4 has been engaged by the T/R circuit.
SCREEN GRID BIAS
The Screen Supply PCB develops the screen grid bias of +495 volts. The secondary of T1
supplies 200 VAC. Diodes D401 & D403 along with capacitors C401 & C402 form a voltage
double circuit. These capacitors charge to 2.828 times the supplied rms175 VAC (175 X 2.828
=495). Zener diodes ZD402 - ZD404 regulate the output voltage. Resistors R402 & R403 are
the bleeder resistors for Capacitors C401 & C402.
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