Emtron DX-3 Service manual
OPERATING MANUAL
EMTRON DX-3
HF LINEAR AMPLIFIER
April 2005
Emtron
DIVISION OF EMONA ELECTRONICS PTY. LTD.
92-94 Wentworth Avenue, Sydney 2010, Australia
Tel. +612 92110988 Fax +612 92811508
www.emtron.com.au
DX-3, Serial No…………
INITIAL SETTINGS FOR PLATE AND LOAD
CAPACITORS
TEST
FREQUENCY
28.600 MHz 10m
24.900 MHz 12m
21.200 MHz 15m
18.100 MHz 17m
14.200 MHz 20m
10.125 MHz 30m
7.070 MHz 40m
3.600 MHz 80m
1.800MHz 160m
1.850 MHz 160m
1.900 MHz 160m
BAND FACTORY SETTINGS
50 OHM LOAD
PLATE LOAD PLATE LOAD
USER SETTINGS
ANTENNA
TABLE 1
2
TABLE OF CONTENTS
1 GENERAL DESCRIPTION..................................................................................................................................................... 5
1.1 DX-3 – INTERNAL VIEW ...................................................................................................................................................... 6
2 TECHNICAL SPECIFICATIONS.......................................................................................................................................... 7
3 UNPACKING ............................................................................................................................................................................ 8
3.1 OPENING THE CARTON ......................................................................................................................................................... 8
3.2 OPENING THE DX-3 COVER .................................................................................................................................................. 8
3.3 INSTALLING THE TRANSFORMER .......................................................................................................................................... 8
4 INSTALLATION ENVIRONMENT....................................................................................................................................... 9
4.1 REQUIRED ENVIRONMENT .................................................................................................................................................... 9
4.2 POWER REQUIREMENTS ........................................................................................................................................................ 9
5 REAR PANEL........................................................................................................................................................................... 9
5.1 POWER / EARTH CONNECTIONS ............................................................................................................................................ 9
5.2 RF CONNECTIONS............................................................................................................................................................... 10
5.3 TRANSCEIVER CONTROL..................................................................................................................................................... 10
6 FRONT PANEL ...................................................................................................................................................................... 10
6.1 CONTROLS ......................................................................................................................................................................... 10
6.2 DISPLAYS ........................................................................................................................................................................... 11
7 ELECTRICAL CONNECTIONS.......................................................................................................................................... 12
7.1 CONNECTIONS TO TRANSCEIVER / EXCITER ....................................................................................................................... 12
7.2 EARTH AND MAINS CONNECTIONS ...................................................................................................................................... 12
7.3 TERMINATING THE POWER CABLE (EXPORT VERSION) ........................................................................................................ 12
7.4 OPERATION AT 230V, 220V, 200V (EXPORT VERSION)...................................................................................................... 12
8 DX-3 DESCRIPTION ............................................................................................................................................................. 13
8.1 RF SECTION ....................................................................................................................................................................... 13
8.2 MAINS TRANSFORMER........................................................................................................................................................ 14
8.3 H. V. POWER SUPPLY ......................................................................................................................................................... 14
8.4 SOFT START MODULE ......................................................................................................................................................... 14
8.5 SENSOR MODULE................................................................................................................................................................ 14
8.6 ANTENNA RELAY / QSK MODULE ...................................................................................................................................... 14
8.7 DISPLAY BOARD ................................................................................................................................................................. 14
8.8 CONTROLLER BOARD ......................................................................................................................................................... 14
9 POWERING UP...................................................................................................................................................................... 16
10 OPERATION....................................................................................................................................................................... 16
10.1 TUNNING PROCEDURE ................................................................................................................................................ 16
10.1.1 General...................................................................................................................................................................... 16
10.1.2 Preliminary tuning..................................................................................................................................................... 16
10.1.3 Final tuning ............................................................................................................................................................... 17
10.1.4. Potential problems during tuning.................................................................................................................................. 18
10.2 ALC ADJUSTMENT ........................................................................................................................................................ 18
10.3 USING YOUR DX-3......................................................................................................................................................... 19
10.3.1 CW / RTTY and all digital modes.............................................................................................................................. 19
10.3.2 Voice modes (SSB)..................................................................................................................................................... 19
10.3.3 Hints on good linearity and efficiency....................................................................................................................... 19
11 SWITCHING THE POWER OFF..................................................................................................................................... 20
12 TROUBLESHOOTING - IF SOMETHING GOES WRONG........................................................................................ 20
12.1 NO POWER .......................................................................................................................................................................... 20
12.2 FAN NOT WORKING............................................................................................................................................................. 20
12.3 IF THE FAULT LIGHT TURNS ON ........................................................................................................................................ 20
3
12.4
OVER-TEMPERATURE CUT-OFF ........................................................................................................................................... 20
12.5 OVER-CURRENT CUT-OFF ................................................................................................................................................... 21
12.6 IG2 BLINKS FAST - NO PLATE VOLTAGE .............................................................................................................................. 21
12.7 SPARKS / DISCHARGES IN RF AREA .................................................................................................................................... 21
12.8 SWR CUT-OFF.................................................................................................................................................................... 21
12.9 FREQUENT OVER-DRIVE PROTECTION CUT-OFF .................................................................................................................. 21
12.10 TUBE REPLACEMENT ...................................................................................................................................................... 21
13 WARRANTY / SERVICE .................................................................................................................................................. 21
14 GLOSSARY......................................................................................................................................................................... 22
15 APPENDIX 1: SCHEMATIC DIAGRAMS ..................................................................................................................... 23
15.1 DX-3 BLOCK DIAGRAM ..................................................................................................................................................... 23
15.2 CIRCUIT DIAGRAM – HIGH VOLTAGE POWER SUPPLY.............................................................................................. 24
15.3 CONTROL BOARD AND ADJUSTMENT POINTS..................................................................................................................... 25
15.4 CIRCUIT DIAGRAM – AC INPUT AND WIRING DIAGRAM – STANDARD ..................................................................... 26
15.5 CIRCUIT DIAGRAM – AC INPUT AND WIRING DIAGRAM – U.S. VERSION ................................................................. 27
15.6 CIRCUIT DIAGRAM – SOFT START (200 TO 240 V OPERATION) ................................................................................. 28
15.7 CIRCUIT DIAGRAM – QSK ................................................................................................................................................. 29
15.8 CIRCUIT DIAGRAM – RF MODULE ................................................................................................................................... 30
15.9 CIRCUIT DIAGRAM – CONTROL BOARD ........................................................................................................................ 32
15.10 CONTROL BOARD – COMPONENT LEGEND (SILKSCREEN TOP)................................................................................ 33
CONTROL BOARD – SOLDER SIDE TRACK WORK............................................................................................................................ 34
16 APPENDIX 2: WAVEFORMS .......................................................................................................................................... 35
16.1 QSK (OPTIONAL MODULE) SWITCHING.............................................................................................................................. 35
16.2 LINEARITY ......................................................................................................................................................................... 35
17 APPENDIX 3: ADJUSTMENTS ....................................................................................................................................... 36
17.1 CONTROL BOARD ......................................................................................................................................................... 36
17.1.1 PRE-BIAS ADJUSTMENT (Adjustment: POT7, marked PRE_BIAS)....................................................................... 36
17.1.2 BIAS ADJUSTMENT (Adjustment: POT3, marked BIAS)......................................................................................... 36
17.1.3 SWR Protection adjustment....................................................................................................................................... 37
17.1.4 EBS ADJUSTMENT (Adjustment: POT4, marked EBS). .......................................................................................... 37
17.1.5 SCREEN VOLTAGE ADJUSTMENT (Adjustment: POT2, marked SCREEN) ......................................................... 38
17.1.6 SCREEN CURRENT LIMIT ADJUSTMENT (Adjustment: POT1, IG2LIMIT)........................................................ 38
17.1.7 IPTRIP ADJUSTMENT (Adjustment: POT6, marking: IP TRIP)............................................................................. 38
17.2 DISPLAY BOARD ADJUSTMENTS .............................................................................................................................. 40
17.2.1 PLATE CURRENT (Adjustment: VR4, Marked: AMP)............................................................................................. 40
17.2.2 PLATE VOLTATE (Adjustment: VR2, marked: VOLT)............................................................................................. 40
17.2.3 REFLECTED POWER (Adjustment: VR3, marked: RF R) ....................................................................................... 40
17.2.4 FORWARD POWER (Adjustment: VR1, marked: RF F)........................................................................................... 41
17.2.5 SCREEN CURRENT (Adjustment: VR6, marked IG2+, VR5, marked IG2-)............................................................ 41
17.3 RF SENSOR ADJUSTMENT ........................................................................................................................................... 42
4
DX-3 LINEAR AMPLIFIER
Serial No …………
OPERATING MANUAL
April 2005
CAUTION
The DX-3 has been designed for 100% safe operation and long life. Interlocking
sensing circuitry constantly monitors conditions inside the amplifier. It must be
noted however, that the high voltages present inside the DX-3 are EXTREMELY
DANGEROUS. Do not remove the top cover under any circumstances if any leads
are still plugged into the rear of the amplifier - especially if the AC lead is plugged in
the power outlet.
Before any component inside the high voltage, power
supply or output section is touched, unplug all rear panel leads and
allow at least 5 minutes of 'off time'.
by momentarily shorting the tube anode to the chassis with a suitable insulated lead.
After that, you should further check this
1 GENERAL DESCRIPTION
The Emtron DX-3 Linear Amplifier is a 3000 watt average output power, for the 160m through 10m amateur bands
housed in a desk-top cabinet with self-contained power supply and cooling system.
It utilises a single high performance tetrode, type GU78B (4CX3000A), a ceramic metal tube with a plate dissipation of 2500W.
The tube is air cooled by a commercial grade forced air turbine blower system under the chassis and a computer type fan sucking
air and positioned above the tube. Both fans operate at two speeds, controlled by a temperature sensor.
Tetrodes offer exceptionally stable operation and levels of quality performance far exceeding that which can be expected from
triodes. The harmonic output and intermodulation distortion achieved with this tube are exceptionally low. This is especially
important when dealing with a high output power.
The Emtron DX-3 is supplied as standard with a host of features including solid state metering, comprehensive
and very long duty cycle.
In addition, a unique Emtron QSK module allows for extremely rapid switching times between transmit and receive, with
consequent advantages when using CW or the digital modes. QSK is standard in all DX-3 amplifiers.
Operation of the DX-3 is greatly simplified by the absence of meter switching, mechanical display and front panel level setting
controls. The front panel moving LED display systems indicate simultaneously: the output forward and reverse power, screen grid
current (positive and negative), the plate voltage and the plate current, while 5 single LED’s indicate: Ready, Overdrive warning,
High SWR cut-off indication, On Air and Fault.
The Emtron Electronic Bias Switch (EBS) automatically switches the standing current (typically 0.75 A) off when there is no
modulation. This reduces the average tube dissipation.
On initial switch on, the unique Emtron "soft start" circuitry ensures that no damaging AC surge currents are generated.
Professional, fine output tuning adjustment is possible, due to the 6: 1 reduction mechanism fitted.
(9 bands),
protection systems
5
1.1 DX-3 – Internal View
CORS
The main components of a DX-3 amplifier are shown in the picture below.
SOFT START
BLOWER
RF SENSOR
QSK
Temperature Sensor
RF CHOKE
CONTROL
BOARD
TERMINAL BLOCK,
SOFT START
HIGH VOLTAGE
POWER SUPPLY
SAFETY
MI
DISPLAY
WITCH
POWER
ON / OFF
Tetrode GU78B
(4CX3000)
TANK COIL
10-30 m
TANK COIL
40 -160 m
BAND
SWITCH
STANDBY /
OPERATE
SWITCH
BAND
SELECTOR
PLATE
TUNING
LOAD
TUNING
6
2 TECHNICAL SPECIFICATIONS
FREQUENCY COVERAGE: Complete (manually tuned) coverage of the nine HF amateur bands:
1.800 – 1.900 MHz
3.500 – 4.000 MHz
7.000 – 7.500 MHz
10.000 – 10.300 MHz
14.000 – 14.350 MHz
18.000 – 18.500 MHz
21.000 – 21.500 MHz
24.000 – 24.500 MHz
28.500 – 29.990 MHz
TRANSMITTING MODES: Both continuous and low duty cycle modes are supported. That is, the DX-3
supports SSB, CW, AM, FM, RTTY and SSTV. II
OUTPUT POWER: Typical 3000 watts carrier or up to 4000 W PEP
DRIVE POWER: Nominal 60-90 watts for full rated output.
INPUT IMPEDANCE: Nominal 50 ohm passive impedance, unbalanced. VSWR 1.4:1 or less.
OUTPUT IMPEDANCE: Nominal 50 ohm passive impedance, unbalanced. VSWR 2.6:1 or less.
DISTORTION: Third order intermodulation products are more than 35 dB below rated output.
HARMONICS: Harmonic output is better than 50dB below the rated output.
FAULT PROTECTION: The comprehensive fault protection system include circuitry to monitor:
• plate current: should the plate current exceed a safe value, the amplifier goes to standby mode for 2
minutes.
• screen grid over-current: Absolute tube protection is offered with visual warning and a reduced power
level being enabled if the screen current exceeds a pre-set limit.
• temperature: Should the tube's temperature exceed a specific level, amplifier operation is suspended
until the temperature drops to a safe level.
• Flash-over: a 3-stage protection circuit using extremely fast MOV’s protects the screen regulator from
the dangerous plate voltage in case of a flash-over in the tube.
OPERATIONAL PROTECTION
• Overdrive protection: Should the DX-3 be overdriven, a LED warning indictor will light up when the
linearity limit is reached. If the drive is increased further, a 2 second cut off (by-pass) will follow.
• SWR protection: Should the DX-3 sense an SWR exceeding 2.6:1, a LED warning indicator will light
up, simultaneously with a 3 second cut off.
METERING: The front panel moving LED display systems indicate:
“Moving light” LED indicators:
• output power
• reflected power
• screen grid current
• plate voltage
• plate current
7
Five single LED’s:
• on air
• ready
• fault
• overdrive warning
• SWR cut-off indicator
ALC: Negative going, adjustable output level.
EBS: Electronic Bias Switch - automatically switches the standing current (about 0.75 A) to a lower ("pre-
bias") value - when there is no input drive.
PRE-BIAS: A small current will flow in the tube when the amplifier is keyed on, but there is no modulation.
This will prevent a harsh sound at the beginning of each word, when the EBS is activated and the tube goes
through a non-linear zone, before reaching the correct initial bias.
QSK: is a module that makes possible the antenna switching at very fast rate - typically 3ms switching time
in each direction. Fitted as standard in all DX-3’s.
SOFT START: when switched on, the mains power is gradually applied to the transformer, over a period of
about 5 seconds, to avoid the high in-rush current typical for such high loads.
COOLING: forced air cooling, two fans, two speeds, temperature controlled
OPERATING TEMPERATURE: 0 to 40° Celsius
FUSING: Two 30A normal acting fuses on the rear panel
DIMENSIONS: 435mm wide, 190mm high, 465mm deep
WEIGHT: 18 kg (40 lb) unpacked + Transformer 25 kg (56 lb) unpacked
3 UNPACKING
The DX-3 is packed in a heavy duty package easily sufficient to protect the amplifier during transportation,
even in case of fairly rough handling.
3.1 Opening the carton
When opening the packing, do not cut the carton. Save the packing material for possible further re-use.
Shipment of your DX-3 in other than factory packing may result in non-warranty damage.
3.2 Opening the DX-3 cover
An inspection of the interior of the amplifier should reveal no damage or adversely affected components.
Remove the 4 screws on each side and remove the cover. Should there be any form of problem, notify your
supplier immediately.
3.3 Installing the transformer
Make sure the transformer is wired for the nominal mains voltage in your area. See 7.4
Two people are needed to install the transformer. The best is to put the DX-3 on a flat, smooth surface such as
a bench or a table top, covered by a small carpet of a folded blanket, so that it can be moved by sliding it on
the table.
Remove the screws holding the base plate in the amplifier. Make sure the holes in the plate remain aligned
with the holes in the bottom of the chassis. Lift the transformer and lower it into the chassis, positioned with
8
the 12-pin connector towards the front of the amplifier. Put the transformer in at a slight angle (about 10
degrees), so that it does not touch the section of the wire loom between the control board and the front panel
display. Mind also the micro-switch, the front panel switches and the control board at the back. See picture on
page 6.
Move the transformer close to the front panel (do not slide it on the base plate – lift it and move). This will
create more space at the back, so that the high voltage wires can be connected. Plug the two wires from the
high voltage power supply into the 2 pins at the lower part of the transformer. Connect also the 4-way
connector and the orange / black wire.
Move the transformer all the way to the rear, to create more room at the front.
Plug the 16-way connector into the display board. If the wire loom has an 18-way female connector fitted, the
2 bottom positions are not used. Make sure the VIOLET wire is at the top and the GREEN wire at the bottom.
Move the transformer to the middle position, trying to line up the holes in the transformer with the holes in
the chassis and the mounting plate. When the holes line up, pull the amplifier so that it overhangs, about 1/3
on the desk and 2/3 out. Make sure somebody is helping during this operation. The back of a chair of suitable
height can be used to help support the amplifier, but make sure someone else is holding it firmly in position.
Insert the screws and washers from underneath. When all 4 screws are in, tighten them firmly using a large
size Philips screwdriver.
Connect the 2 mains wires to the terminal block of the soft start module. See picture, Page 6.
Put the cover back and the installation is complete.
4 INSTALLATION ENVIRONMENT
4.1 Required environment
The DX-3 amplifier can be operated at an ambient temperature between 0 and 40° Celsius. It should be
installed in a place with good ventilation and protected from the direct sunlight. At least 5 cm (2”) of free
space must be left at the left and right of the amplifier for ventilation. Do not place any object on top of the
amplifier, especially above the ventilation opening.
An environment free of dust, smoke and high humidity is required, as for any high powered RF amplifier.
Dust or particles resulting from burning fire wood or coal could be responsible for sparks or electrical
discharges between the capacitor plates, or in other parts of the RF section.
4.2 Power requirements
When operating at full power, up to 30A from the 240 VAC mains is required. Ensure that the AC supply you
intend to use is fully rated and properly fused. The Emtron "soft start" circuitry ensures that there are no
momentary surges of current at power-up, therefore the fuse does not need to be over-rated. However, the
wiring of the mains supply for the amplifier should be able to handle the power at full load with minimal drop
in the voltage, to insure the performance of your DX-3 does not suffer.
5 REAR PANEL
The following connectors and controls are present on the rear panel
5.1 Power / Earth connections
A wing-nut Earth connection is provided at the rear of DX-3. A good Earth link must be provided here.
Connect this first, before making any other connection to the amplifier. Two fuse holders are fitted along with
30A, normal acting fuses.
9
5.2 RF connections
RF INPUT
The RF input is an SO-239 female connector. A 50 ohm coaxial cable line of good quality terminated with a
PL-259 coaxial connector is required to connect the transceiver or exciter output to the input connector of
your DX-3 amplifier.
RF OUTPUT
The RF output is also a female SO-239 connector. The use of a high quality RG-8A/U, RG-213 or similar 50
ohm coaxial cable line terminated with a ‘VHF’ type PL-259 connector is essential. Similarly, a VSWR of
2.6: 1 or better is mandatory. Remember too, that the EMTRON DX-3 amplifier can deliver 3000 W
continuously and up to 4 kW PEP in the SSB mode. Not all antennas can handle such power.
5.3 Transceiver control
ALC
The ALC output is via a black female RCA connector.
This is an ALC system for use with transceivers or transmitters having a negative-going ALC system and
possessing an external ALC input jack. A shielded patch lead with an appropriate connector at one end and a
male RCA connector for the DX-3 at the other end is required. Check the specifications of your transceiver
for a suitable connection.
PTT
The PTT input is a female RCA connector (red). This line controls the transmit / receive switching system.
This jack must be connected to transceiver or exciter relay contacts which are open on RECEIVE and closed
on TRANSMIT. The voltage at the PTT input is typically 28V loaded (up to 35V unloaded), with an
impedance of about 240 ohm. A current of about 0.12 A has to be switched by the transceiver or exciter.
ALC CONTROL
This is a user-accessible control for setting the negative voltage at the ALC output. Further details are given
in section 10.2
6 FRONT PANEL
The following controls and indicators are present on the front panel:
6.1 Controls
BAND SWITCH
A nine position switch selects the desired frequency range. The operating bands are indicated in metres.
PLATE TUNE
Tunes the amplifier operating frequency. A chart of approximate starting settings is given in Table-1
LOAD TUNE
Tunes the amplifier output loading. A chart of approximate starting settings is given in Table-1
ON/OFF
Switches the AC power on and off. On initial switch on, the standby mode is enabled. Note also the
appropriate switch down sequence, given in Section 11.
OPR/STBY
Enables the amplifier once it has warmed up. In STANDBY mode, the screen voltage is removed and any RF
power applied to the input, is bypassed to the output. If this switch is changed to OPERATE before the
READY light comes on, the FAULT light will turn on. This is not a fault, but it is better to leave the switch in
STBY position until the amplifier is ready to operate.
10
6.2 Displays
)
All the DX-3 indicators are concentrated in a single, solid state, “moving LEDs” display (See drawing). The
following values are displayed (top to bottom):
Output Power - Scale up to 4 kW, non linear. Yellow LED’s with red indicating power over 3kW.
Reflected Power - Scale up to 500W, non linear. The colour is green, yellow and red, indicating
progressively higher reflected power and possibly problems with your antenna.
Ig2 - Zero-centred display. The left (green) side has a full scale of about 25 mA of negative screen current.
The right (red) side has a full scale of about 50 mA of positive screen current. Above this value, the red LEDs
will flash, warning you to increase the loading, or reduce the drive. At about 60 mA, the protective current
limiting will cut in.
Plate Voltage - Scale up to 3.5 kV, green.
Plate Current - Scale up to 2.4 A. Yellow, with a green zone indicating the standing current bias (when EBS
is disabled only. NOTE: the factory adjustment could be slightly different from the green zone indication).
The area above 2.4 A is red. It indicates excessive plate current, due to high drive level and improper tuning
(especially plate tuning – see “Tuning” chapter, 10.1)
ON Air - single LED, green. When pressing PTT, this LED turns on (while in OPERATE)
READY - single LED, yellow. Turns on at the end of warm-up period, when the mains power to DX-3 is
switched on. It turns off for about 2 minutes if the plate current protection is triggered. In this case, the
FAULT light also turns on.
FAULT - single LED, red. Turns on in 3 situations:
• when the over-temperature protection is triggered, the FAULT turns on until the tube cools to a safe
level. During this time, the operation of the amplifier is disabled, the screen voltage is off and any RF
power applied to the input is bypassed directly to the output.
• when the over-current protection is triggered, FAULT turns on for 2 minutes, while READY turns off
• at DX-3 power up, if the OPR/STBY switch on the front panel is left in OPR position. The FAULT
light will go off when the DX-3 is ready for operation, after warm-up.
SWR - single LED, red. A three second cut-off will happen if your antenna has a SWR worse than 2:1
(typical 2.6:1) at the operating frequency. During the cut-off, the RF from the input is directly by-passed to
the output.
OVER-DRIVE - single LED, yellow. Flashes when the input drive is exceeding the linear operation level. If
even more drive is applied, the overdrive protection will cut off the operation (bypass) for about 2 seconds.
NOTE: the input drive at which the indicator turns on depends on a certain extent on the tuning.
RF OUTPUT POWER (kW)
OVER
DRIVE
REFLECTED POWER (W
SWR
ON AIR
READY
FAULT
Figure 1. Front Panel Display
11
7 ELECTRICAL CONNECTIONS
(Op
)
7.1 Connections to Transceiver / Exciter
Signal connections
Before making any connections, ensure that DX-3 is not connected to AC power, and the transceiver is not
transmitting. Connect the antenna first to the DX-3 output. Then connect the transceiver output to the DX-3
RF input. Plug the PTT lead into the RCA socket marked PTT on the rear panel. If required, connect the
ALC. (In most cases there is no need for ALC – see 10.2)
The most appropriate interconnection layout is shown in Figure 2 below. In this set-up, the transmit/receive
relays in the DX-3 are controlled directly by the transceiver or exciter.
TO ANTENNA
EMTRON
DX-3
RF
IN
PTT
Relay
Input
ALC
RF
OUT
tional
RF
OUT
ALC
Station
Transceiver
PTT
Relay
Output
Figure 2. Connections between DX-3 and Station Transceiver
7.2 Earth and mains connections
Power connections
Before connecting any power to the amplifier, make a good Earth connection to the screw with wing nut at
the rear of DX-3. Make sure the POWER switch on the front panel is in the OFF position. Then plug the
power cable into the power outlet.
7.3 Terminating the power cable (export version)
As different countries have different standards for their power connections, the DX-3 amplifiers exported
from Australia are supplied with an un-terminated power cable.
The green / yellow wire is connected to the amplifier chassis and MUST be connected to the safety ground
of the AC mains supply. It must NEVER be connected to one of the AC “hot” wires. The Brown and Blue
wires connect to the mains transformer inputs. The brown wire is “active” or “live”. The blue wire is the
mains neutral. Both wires are fused.
7.4 Operation at 230V, 220V, 200V (export version)
The Emtron DX-3 will normally arrive pre-set for the power source of the country the amplifier has been sold
to. However if operation to another mains voltage is required, the appropriate connection changes will be
needed.
Figure 3 shows the transformer connections for 200V, 220V, 230V and 240V operation. If a change is
required, this should be done only by a qualified technician, after taking all the necessary safety precautions.
See CAUTION on page 1.
PLEASE NOTE: The DX-3 should not be connected to a mains supply of less than 200VAC!
12
240V:
230V:
220V:
200V:
0
0
0
2000
200
220
220
230220
230
230 220
240
240
240
240
0
200
230 220
240
Figure 3: TRANSFORMER AC INPUT CONNECTIONS
8 DX-3 DESCRIPTION
8.1 RF Section
The RF section occupies the right hand side of the DX-3 (looking from the top - front). See picture in 1.1.
RF Switch and tuned circuits
At the front of the amplifier are two variable capacitors, for plate and load tuning. A 9-position ceramic
switch is employed for the 9 operating bands. Next to the switch is the 40 to 160 metre tank coil. The silver
plated, large diameter copper tube is the 10 to 30 metre tank coil.
RF Sub-chassis
The GU78B tube is positioned on a separate RF sub-chassis. All the connections to the tube, except for the
plate, are under this sub-chassis. A 9-way heavy duty connector is used for the outside connections. The fan
blows air into this sub-chassis, which is forced out through the ventilation fins of the tube. A second fan
above the tube helps by sucking the air out. The air temperature is sensed by 2 sensors placed above the tube
(they can be seen between the fins of the top fan). The sensors must stay in a position close to horizontal.
Make sure you are not pushing them down, too close to the tube, as high voltage exists between them.
13
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