OM POWER OM2500 A User manual

Instruction Manual
OM2500 A
SHORTWAVE POWER AMPLIFIER
OM POWER, s. r. o. 930 30 Báč126
SLOVAKIA
E-mail: [e-mail]

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TABLE OF CONTENTS
1. GENERAL INFORMATION
1.1. Introduction ………………………………………………………………... 4
1.2. Specification ……………………………………………………………..... 4
1.2.1. Parameters …………………………………………………………………. 4
1.2.2. Protection Circuits ………………………………………………………… 4
1.2.3. Indicators ………………………………………………………………….. 5
2. SAFETY INSTRUCTIONS ……………………………………………… 5
3. GENERAL DESCRIPTION ………………………………………………. 7
3.1. HF part ……………………………………………………………………. 7
3.2. Power Supply …………………………………………………………….. 8
3.3. Safety Devices ……………………………………………………………. 8
4. INSTALLATION ………………………………………………………… 8
4.1. Grounding ………………………………………………………………… 8
4.2. Coaxial Cable …………………………………………………………....... 9
4.3. I/O Box and Interface ……………………………………………………... 9
4.4. Mains Supply ……………………………………………………………… 12
4.5. Cooling ……………………………………………………………………. 12
4.6. Remote Control …………………………………………………………… 12
5. OPERATION ……………………………………………………………… 12
5.1. Operation Elements ……………………………………………………….. 13
5.2. Configuration of Power Amplifier ………………………………………... 15
5.2.1. TCVR Support Settings …………………………………………………… 15
5.2.2. Connection with no supported TCVRs ……………………………………. 16
5.2.3. Communication Loss ……………………………………………………… 17
5.2.4. Antenna Switching Menu …………………………………………………. 17
5.2.5. Bandpass Filter Settings …………………………………………………… 18
5.2.6. Loading Factory Default Settings …………………………………………. 18
5.2.7. MUTE Option ……………………………………………………………… 19

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5.2.8. LCD Settings Menu ……………………………………………………… 20
5.2.9. Operation in MANUAL Mode ………………………………………….. 20
5.3. Tuning of Power Amplifier …………………………………………….. 20
5.3.1. AUTO or MANUAL …………………………………………………… 21
5.3.2. Manual Tuning Instructions …………………………………………….. 21
5.3.3. Tuning Adjustment ………………………………………………………. 23
6. MAINTENANCE ………………………………………………………. 24
6.1. Indication of Fault Conditions …………………………………………. 24
6.2. Fuse Replacement …………………………………………………….... 25
6.3. Tube Replacement …………………………………………………....... 25
6.4. Cleaning ……………………………………………………………….. 25
7. APPENDIX …………………………………………………………….. 26
7.1. Example of connection for ICOM ……………………………………… 26
7.2. Example of connection for ELECRAFT ………………………………… 27
7.3. Example of connection with YAESU …..……………………………… 28
7.4. Example of connection with Antenna switch and BPF …………………. 29
7.5. Example of connection USB micro KEYER II
with IC7800 or IC7700 ……………………………………………....... 30
7.6. Example of connection USB micro KEYER II
with another Icom ……………………………………………………….. 31
7.7. Example for connection USB micro KEYER II
with Yeasu or ELECRAFT ……………………………………………. 32
7.8. Example of connection PA with MicroHAM MKII, (MK2R+ etc )
with CI-V output ....................................................................................... 33
7.9. Block Diagram of OM2500A Power Amplifier (USA version)................. 34

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1. GENERAL INFORMATION
1.1. Introduction
The OM Power model OM2500A is a fully automatic power amplifier, designed for use on all
short wave amateur bands from 1.8 to 29.7 MHz (including WARC bands) and all modes. It is
equipped with one GU84b ceramic tetrode.
THE ADVANTAGES OF OM2500A
Full compatibility with: ICOM, ELECRAFT, KENWOOD, TEN-TEC ORION, YAESU
and Icom transceive protocol using by MicroHAM devices ( CI-V output ).
Automatic switching between bands
Automatic tuning within the band according to segments
Automatic switching of band pass filter
Automatic switching of antenna switches
The possibility to use 2 different antennas within one band or segment
1.2. Specification
1.2.1. Parameters
Frequency Coverage Amateur Bands 1.8 – 29.7 MHz including WARC
Power Output 2500 W in SSB and CW, 2000 W in RTTY, AM
and FM
Input Power Usually 60 to 80W for full output power
Input Impedance 50 Ohm, VSWR < 1.2 : 1
Power Gain 17 dB
Output impedance 50 Ohm unbalanced
Maximum output SWR 2:1
SWR protection: Automatic switching to STBY , when reflected power is
350Wor higher
Intermodulation distortion 32 dB below nominal output
Suppression of harmonics < -50 dBc
Tuning Manual or AUTO
Response speed of AUTO Less than 0.5 sec within the same band
Less than 3 sec. if out of the band
Tube GU84b Ceramic tetrode
Cooler Centrifugal blower + axial blower
Power supply 2 x 230 V - 50 Hz one or two phases
Transformers 2 pcs of toroidal transformer 2,0 kVA
Parameters 485 mm x 200 mm x 455 mm
(width x height x depth)
Weight 40 kg
1.2.2. Protection Circuits
There are 8 special protection circuits used in the amplifier. They are activated when one or
more of next parameters exceed defined values or some unwanted occasion occurs.

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·VSWR too high
·Anode current too high
·Screen current too high
·Grid current too high
·Mistuning of PA
·Hot switching protection
·Soft start for protecting your fuses
·“switch-on blocking “ at opened amplifier
1.2.3. Indicators
There are couples of LED and bar graph indicators visible on the front panel to inform you
about value of some parameters or operation status:
Bar graph indicators Power output - 50 LED
Reflected power – 20 LED
Current at screen Ig2 – 10 LED
Anode voltage, anode current, tuning – 30 LED
LED Indicators Current at control grid (Ig1 – 2 LED)
WAIT – preheating of tube (150 sec)
STBY – standby
OPR – operation condition
FAULT – failure, switching off for abt. 4 sec
INHIBIT - operating condition
ANT 1 - which ANT is in use
ANT 2 - which ANT is in use
ANT - ANT selection
Buttons UP – DWN - listing in menu
MAN - manual operating
AUTO - automatic operating
TUNE - tuning
SET – confirms selected parameter
OSD Indicator LCD Display 2 x 16 characters
2. SAFETY INSTRUCTIONS
WARNING!
DANGEROUS HIGH VOLTAGE!
The power amplifier is using high voltage up to 2800V DC, which is very dangerous for
human life! Read next safety instructions carefully first, before you will start to install
and operate power amplifier! NEVER VIOLATE NEXT RULES!

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WARNING! NEVER ALLOW CHILDREN to play around PA or to touch power
amplifier or connected cables in working condition, or to push anything into the case
holes!
WARNING! The amplifier contains high voltage circuits. Never turn the amplifier on
without the upper lid in place. DO NOT ATTEMPT TO SHORT OR BYPASS safety
switch under upper lid!
WARNING! OM2500 HF amplifier can be operated ONLY if both of supply cables are
connected! The amplifier reaches optimal parameters in 2 phase’s system, if you do not
have 2 phases, connect both mains cords into the same phase.
WARNING! The OM2500A amplifier is neither to be used in a WET or HUMID
environment nor to be exposed to RAINFALL!
WARNING! Do not turn the amplifier on without having connected the ANTENNA or
properly rated DUMMY LOAD! A hazardous HF voltage may build up on the antenna
connector after turning the amplifier on with no antenna or dummy load connected!
WARNING! Before opening the upper lid of the amplifier make sure that power supply
has been disconnected AT LEAST 5 minutes allowing the electrolytic capacitors to
discharge fully. Disconnect power cord from the outlet!
CAUTION! The amplifier must be installed in such a way that free flow of hot air from
the tube is allowed. The amplifier must not be installed in a constrained surrounding
(i.e. tight shelves etc.). During long time operation ventilation grid can reach high
temperature. Do not touch the top cover of the PA in these places during operation.
CAUTION! The amplifier must be properly grounded during operation.
CAUTION! During operation the amplifier must be installed in such a way that the rear
side remains accessible.
CAUTION! The amplifier is an A category product. In a household it can influence
other electric appliances. In such cases the user is to take proper actions to mitigate this
disturbance.
CAUTION! Make sure that all screws holding the case together are properly in place
and tightened before carrying the amplifier with the handles.
CAUTION! Read this manual carefully. Fallow all of instructions during installation
and operation to avoid damage to the amplifier not covered by manufacturer´s
warranty! Do not attempt to perform any change of hardware or software!

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3. GENERAL DESCRIPTION
3.1. HF part
In this amplifier a tetrode GU 84b is used in a grounded-cathode circuit (input into control
grid). This amplifier achieves excellent linearity by the voltage stabilization of the control
grid bias and the screen voltage. The power input is given to the control grid, using a
broadband input circuit with an input impedance of 50 Ohms. This adaptable input circuitry
ensures a good input SWR (better than 1.2:1) on all amateur bands.
The output of the amplifier is a Pi-L circuit. The ceramic capacitor for TUNE and LOAD are
divided. This enables the amplifier to be tuned exactly and makes it possible to easily return
to the previously set positions after band changes.
Top view on the opened OM2500A
Tetrode GU84B PWR meter Blower Switch-on board
Output Pi-L Circuit Tuning capacitor Power supply board
Subpanel

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3.2. Power Supply
Power supply of the amplifier is comprised of two of 2,0 kVA toroidal transformers. A soft
start is provided using relays and resistors.
The high anode voltage is made by combining 8 x 350 V (total 2800V) @ 2A. Each has its
own rectifier and filter. In the high voltage circuit, safety resistors are employed to protect the
amplifier against overload.
The source for screen grid is regulated by parallel stabilization with BU941 NPN Darlington
transistors and delivers a voltage of 350V at 100mA.
The -120V for the control grid is regulated with zener diodes.
3.3. Safety Devices
Control and monitoring circuits ensure control and safety during malfunctions of the PA.
These are on the Control board, which is located on the chassis subpanel.
4. INSTALLATION
NOTE
Read this chapter carefully prior you will start installation. Before unpacking inspect shipping
woody container first, if it is not damaged. Keep all of packing parts for possible future
shipment. Check unpacked power amplifier. If you find some damaging, contact your dealer
immediately to keep full warranty.
During installation go step by step according to next parts.
4.1. Grounding
CAUTION
The amplifier has to be grounded properly! Connect the screw on the rear panel of the
amplifier to your local grounding system with a copper cable; use a cross-section of 4
mm2at least.
Connect your transceiver to the same grounding system of your shack carefully!
Use minimum length cables and make certain that the connections are both physically and
electrically sound. With poor grounding, you may risk damaging your equipment, having
problems with TVI/BCI or your transmitted signal may be distorted.

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4.2. Coaxial Cable
The output of the transceiver is to be connected to the input of the amplifier via RG58 or
similar cable. For the connection between the power amplifier and the antenna, RG213 or
similar coaxial cable suited for high power is recommended. Both the INPUT and OUTPUT
SO-239 sockets with Teflon insulation is used.
Rear view of the amplifier OM2500A
AC Sockets Fuses OUTPUT
REMOTE I / O Interface INPUT
4.3. I/O Box and Interface
Control of Amplifier and communication with TCVR as well as Antennas / BPF switching
can be done via the rear panel I/O Interface.
Control cable maintains TX / RX switching of the PA (TX GND). The cable is shielded. On
the side of the power amplifier a CINCH-socket is used. On the side of your transceiver you
have to use a socket suitable for this transceiver. During transmitting the middle pin is
connected to the ground.
The relays of the OM2500A have to be switched earlier than HF is applied (cold switching).
Modern transceivers they have a time delay between PTT switching and power output.
CAUTION
If you are using and older transceiver or transmitters without time delay, we
recommend to connect the PA in such a way that the transmit/receive switch (foot switch
for example) is connected with the KEY IN socket of the amplifier. The KEY OUT
socket is to be connected with the PTT socket at the transceiver.
The amplifier is equipped with two safety devices, which ensure that the output relay is not
switched under power mistakenly (hot switching).

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KEY IN RCA Phono - Input signal PTT switching voltage / current 5V /2 mA)
KEY OUT RCA Phono - Output signal PTT (maximum switching of 30V / 50mA)
CI-V Mono 3.5mm Jack for connection of ICOM TCVRs or devices that
provide compatible CI-V protocol. Correct baud rate is important.
TCVR DB9 serial port RS232 for KENWOOD, YAESU and ELECRAFT
TCVRs. Correct baud rate and type is required for successful
operation. If both CI-V and TCVR cables are connected then CI-V
disables RS232. Otherwise selection of interface is done via TCVR
type.
PC DB-9 RS232 port is used for communication with your PC. Please use
setting you would normally use if using direct TCVR – PC connection.
ALC RCA Phono – Automatic Level Control is used when tuning the PA to
block drive level.
CAUTION!
We only recommend using ALC feature while operating RTTY, FM and other 100%
duty modes.
CONTROL The CONTROL socket is a single DB-15 connector that provides many
connections to the amplifier from your transceiver. Use shielded cable
for all connections to this connector. You will need to fabricate a cable
with the proper connector for your transceiver or use individual
connectors as described below.

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PIN OUT:
1. ALC Out
2. NC
3. INHIBIT Control voltage
4. TX INHIBIT for Yaesu and Elecraft – this supersedes
ALC output
5. NC
6. KEY OUT
7. NC
8. KEY IN
9. –
15. GND
ANT & BPF SW DB-25 is used for switching of external HP BPF or external Antenna
Switch. Maximum switching of 30V / 0.5A is possible.
PIN OUT:
1. antenna port 1
2. antenna port 2
3. antenna port 3
4. antenna port 4
5. antenna port 5
6. antenna port 6
7. antenna port 7
8. antenna port 8
9. antenna port 9
10. antenna port 10
11. COMMON port of ANT SW
12. NC
13. GND
14. BPF 160m
15. BPF 80m
16. BPF 40m
17. BPF 30m
18. BPF 20m
19. BPF 17m
20. BPF 15m
21. BPF 12m
22. BPF 10m
23. COMMON BPF port
24. NC
25. GND

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4.4. Mains Supply
WARNING!
The power Amplifier OM2500 HF has to be connected TO THE MAINS WITH BOTH
CABLES! The amplifier reaches optimal parameters in the system with 2 phases. Every
phase has to be able to deliver 2.5kVA. If you do not have 2 phases system, connect both
mains cords into the same phase. In such a case system has to be able to deliver 4.5kVA!
CAUTION
Be sure you got PA with properly terminated line cable, corresponding with your power
system’s outlet. If not, contact your dealer. In such a case you should make the necessary
changes using a licensed electrician.
WARNING!
Be sure that your power system is correctly wired and properly rated! To use
adequately sized and connected grounding system is also very important.
4.5. Cooling
CAUTION
The amplifier must be installed in such a way that free flow of hot air from the tube is
allowed. Do not obstruct air intake and exhaust areas of the PA.
The centrifugal blowers provide the necessary cooling of the amplifier, even during long
contests. The main blower is activated by switching the PA on and it is turned off when
cooling is finished (approx. 1-5 min after switching off the PA depending on the temperature
of the tube). The supplemental fan is turned on depending on the temperature of the air exiting
from the amplifier. It is switched on at 70°C and switched off at 60°C.
4.6. Remote Control
Control of the amplifier is possible remotely by using REMOTE BOX (optional).
Connection is done by REMOTE socket, maximum cable length of 10 meters.
5. OPERATION
WARNING!
Before switching PA on, make sure that amplifier is grounded, antenna or dummy load
is connected, line cord is putted to the outlet.
CAUTION
Before switching PA on, check all connections between PA and TCVR.

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CAUTION
Do not turn PA on for at least 2 hours after unpacking it and locating in its operating
location. Especially when amplifier is moved from a cold place to a warm one because
not visible condensation may develop, and this could result in damage to the high
voltage circuits of the PA.
CAUTION
Never try to change antenna output during a transmission to avoid warranty loss.
NOTE
When you decide to have a short operating break, place the amplifier in the standby mode
rather than switch it off.
5.1. Operation Elements
There is couple of operational elements accessible or visible on the front panel.
TUNE - Anode capacitor for tuning, tuning of higher frequencies to "0",
lower frequencies to „100“.
LOAD - Output capacitor tunes antenna load resistance to amplifier.
Capacity is low at „100“ and high at "0" on the scale.
OFF - You switch off the amplifier by pressing this button.
ON - You switch on the amplifier by pressing this button.
After 3min of warm-up delay, the amplifier will be ready for operation.

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OPR/STBY „OPERATE“ sets the amplifier ready for transmit operation.
In STBY, if WAIT-LED is on or the amplifier is OFF, the amplifier
is in bypass-mode and your transceiver is directly connected to the
antenna. Maximum allowed power in bypass mode is 400 Watts!
RF OUTPUT Bar graph – shows output power .
REFLECTED POWER Bar graph – shows reflected power from the antenna.
Maximum level is 350W otherwise amplifier switches to
STANDBY mode.
Ig2 Bar graph – measures the current of the second grid from -20mA to
+80mA.
HV/IP/TUNE Bar graph – measure the anode voltage, anode currency or tuning of the
amplifier.
INHIBIT Indicates interruption of transmission during the tuning process of the PA. If
indicated by RED LED then PA is in STBY mode. If during a retune
operations within the same BAND then the PA will retune according to the
frequency of the transceiver. When changing the BAND – INHIBIT will stay
lit until the KEY IN is released and the tuning process will start. After that PA
is automatically ready for operation.
ANT, ANT1, ANT2 The amplifier is capable of automatic antenna switching (ie. 80m CW
and 80m SSB can be split between two antennas). The amplifier will
automatically select desired antenna by selecting last used antenna on a given
frequency.
SET button for: - MAIN MENU
-Confirmation of selection
-Saving of selected value
-Saving of tuning parameters

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TUNE Push button for selection of TUNE mode
AUTO Push button for selection of AUTOmatic mode
MAN Push button for selection of MANUAL mode
DWN / UP Push button for selection of band, segment or parameter
5.2. Configuration of Power Amplifier
When the ON button is pressed the amplifier will start to heat the final amplifier tube. During
the warm-up period, the STBY and WAIT LEDs will be illuminated. If a transceiver is
connected to the correct port and all communication settings are right, the operating
frequency, AUTO, and the type of transceiver will be indicated on the alphanumeric display.
After successful heating of the TUBE you can enter operating mode by pressing the OPR
button.
Example of Automatic mode with ICOM
TCVR.
Type of supported TCVR and working
frequency are visible on the display.
AUTO LED is ON.
5.2.1. TCVR Support Settings
Supported transceivers: ICOM, ELECRAFT, KENWOOD, TEN-TEC , ORION, YAESU
Press SET button and scroll using UP / DWN to CHOOSE TCVR

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Confirm CHOOSE TCVR by pressing SET again and scroll UP / DWN to your transceiver
type. Confirm the selection by pressing SET
Continue by selecting Baud Rate.
Press SET button and scroll using UP / DWN to BAUD RATE. Press SET again.
Baud rate for TCVR – PA communication is
shown on the LCD display.
By scrolling UP / DWN select desired Baud Rate which must be the same as baud rate used
by your transceiver. (please refer to your transceiver user manual). To confirm your selection
press SET.
When using Yaesu TCVR you need to configure the STOP BIT parameter correctly and
confirm selection with SET.
The communication settings menu can be left by pressing the AUTO button. The amplifier
will enter AUTO mode only if all settings are correct and connection has been established
with your transceiver. You can verify that the correct frequency and transceiver type is shown
on the LCD display.
5.2.2. Connection with not supported TCVRs
For communication with TCVRs, that are not supported by OM2500A (for example JST-245
and older types of Kenwood), an external IF-232 converter is to be used. You can also use
devices from several companies that produce compatible CI-V output which deliver frequency
information in ICOM format through the CI-V output. Then the PA will be connected in the
following configuration:
JST-245 <> DB37- JST-245 cable <> MKII ( or other device which has a CI-V output ) <>
PC. OM2500A is connected to the CI-V output of the CI-V device (MicroHam for example).

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Example of communication
5.2.3. Communication loss
If TCVR is not connected or communication settings are incorrect the message
“COMMUNICATION LOST” will be displayed. You can still use PA by entering MANUAL
mode (MAN Button) or by correcting the transceiver connection problem.
Example of Communication loss message
5.2.4. Antenna Switching Menu
If you have 3rd party external antenna switch connected to your amplifier ( i.e. MicroHAM
TEN SWITCH), you need to configure the assignment of each port to a specific band /or
antenna.
By pressing SET and scrolling to ANTENNA SETTINGS and confirming by SET you get
current band and its antenna selection. By scrolling UP / DWN you can select BAND which
you want to assign to current ANTENNA selected.

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Then select how many antennas you want per current band (1 or 2) and always confirm your
selection by pressing SET. The by scrolling UP / DWN you assign which PORT is used on
your external antennas switch for this particular antennas. (ANT 1 ON PORT 01)
Shall you decide to use 2 antennas for this band then after confirming that with SET
configuration continue to the other antenna selection / port selection.
To finish Antennas switch configuration you can either press AUTO or MAN.
5.2.5. Bandpass filter switching
Switching of external band pass filters is automatic and needs to follow pin out of BPF
connector. For more details see Example of connection with antenna switch and BPF
in Appendix.
5.2.6. Loading factory default settings
In the rare case of needing to restore factory default settings press SET and scroll using UP /
DWN to LOAD DEF VALUES and confirm by SET.

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Then select if you want to erase all settings (pressing TUNE) or just one setting value (SET
button). In the case of resetting a single parameter use UP / DWN to select which option and
confirm by SET.
5.2.7. MUTE option
When operating the OM2500A with an Icom transceiver without TX INHIBIT for disabling
TX, we recommend blocking of the TX while tuning using ALC control (mainly while
operating FM /RTTY/ AM).
The ALC Input of your transceiver should be connected to the ALC Out of OM2500A.
Using SET and scrolling UP / DWN select SET MUTE and confirm it by SET. Then
configure MUTE LEVEL for each band so it results in no power being transmitted by TX
when performing TUNE procedure.

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5.2.8. LCD Settings Menu
By pressing SET and scrolling UP / DWN and selecting LCD CONTRAST (Confirming by
SET) and pressing Up or DWN you can vary the Contrast of the LCD display. Press SET for
confirm the setting.
.
5.2.9. Operation in MANUAL mode
To enter Manual mode of the PA please press MAN. By pressing MAN repeatedly you select
BAND and band segment. You can control the segment or band by scrolling the UP / DWN
buttons.
5.3. Tuning of Power Amplifier
The OM2500A amplifier is operated in class AB. Thus it’s possible to obtain a maximum
output power at excellent linearity. For this purpose the amplifier has to be tuned carefully.
WARNING!
Before starting tuning you have to check if the right antenna or a 50 Ohms load
resistance is connected at the antenna output!
CAUTION
The operation of a mistuned PA will cause malfunctions, the increase of grid current
(the GRID-MAX-LED will light up) and problems with TVI/BCI.