[AMPS] Operating comments using the Emtron DX-2a
km1h@juno.com
km1h@juno.com
Sun, 31 Jan 1999 12:48:52 -0500
On Sun, 31 Jan 1999 10:14:59 -0600 Andy Wallace <andywallace@home.com>
writes:
>
>Carl--
>
>Is this a good amp? Or does it need all sorts of "mods" to work
>properly?
>
>Andy K5VM
How should I know since it is a brand new player on the block, or are you
just being sarcastic?
OTOH, the description would tend to place it into serious contention. I
havent bought a new amp since 1987 and this is one I would have to
consider.
A concern down the road would be repair parts availability which has had
a resale price impact on several imports.
73 Carl KM1H
>
>K1WPO@aol.com wrote:
>
>> General Technical Comments of Emtron DX-2a
>> (http://www.emtron.com.au/AmpDX2D.html)
>>
>> I received one of the first DX-2a shipped to the U.S. a few months
>ago, and
>> have been pleased with the performance,
>> value and performance. Several friends have asked about
>> the amplifier, so without a lot of technical measurements,
>> etc, the following are my general, non-technical comments.
>>
>> Tube
>> This amplifier uses a Svetlana 4CX1600B
>> (http://www.svetlana.com/docs/tubeframe.html) running in class AB1.I
>prefer
>> the use of a single, 1600 watt plate dissipation tube over two (or
>even three)
>> tubes in parallel. This tube is the tetrode equivalent of an 8877,
>which has
>> always been an expensive tube. The lower cost allows a better 2KW
>amplifier at
>> significantly lower cost.
>>
>> P/S
>> The power supply is robust, with a very large and well
>> constructed transformer. The unit I received was an export (50Hz)
>model. Later
>> versions should provide some weight savings when a 60Hz transformer
>is
>> available. The rectifier diodes are typical series string as a F/W
>bridge, and
>> use the large 6 ampere variety.
>> B(-) fault diodes are used to GND as well as B(+) glitch
>> resistors, all located on a very compact HV P/S module.
>> The entire P/S is removable with two screws and six push on
>terminals, no
>> soldering - a very neat, compact design.
>> Operation is silent, with no transformer hum or lamination
>> noise. Idle voltage (bleeder load only) is around 3,200Vdc
>> (at 245Vac in) and full load at 1.0 ampere is about 2,900 Vdc.
>>
>> AC Input
>> The six foot cord set is a little light by American
>> standards, and has a vinyl sleeve. I looks like the
>> equivalent of 15-16 AWG. Australia rates it at 25 amperes,
>> which is adequate, but I prefer a real, American cordset.
>> I replaced mine with a longer (8ft), more flexible, rubber> 14-3
>SJOW cordset.
>> The amp ships without an end plug, so
>> You will need to supply what ever you're using at your shack for
>your 240Vac
>> mains. Since there are no 120Vac components used internally, and the
>cordset
>> is three-wire, the GND is tied directly to chassis at the input. The
>two HOT
>> leads go first to 20 ampere fuses accessible at the rear panel. HOT
>then
>> proceeds to the cabinet interlock, and front panel switch which
>carries only
>> relay solenoid current. Both sides are then switched through a
>large, 277Vac
>> 25-ampere contactor to a proprietary soft-start thyristor circuit,
>which
>> generates a true AC ramp function. The soft start takes about 2
>seconds to
>> complete, and operates the entire amplifier. Everything from the
>meter lamps,
>> to the tube filament (12.6V) and the HV p/s are ramped. The AC input
>is wired
>> with heavy, short runs, and is done better than most AC input
>circuits I have
>> seen. Attention seems to have been paid to minimizing AC input
>losses through
>> adequately sized conductors and terminations.
>>
>> RF Deck
>> The RF deck components are large by today's standards. All
>> wiring components, straps, taps, coils, etc are silvered.
>> The L1 tank coils are entirely wire-wound, toroids are not
>> used for the lower bands. Coils for the upper HF bands are
>> heavy, 1/4 inch silvered stock, and for the lower bands
>> are silvered #8-10 wound and mounted on a heavy ceramic form.
>> Ceramic/porcelain standoffs are used throughout, something you don't
>see too
>> often in today's amplifiers.
>> Workmanship around the tank wiring and taps is excellent. The size
>and quality
>> of the components and workmanship are similar to the old ETO
>77dx.The band
>> switch is a five deck silvered ceramic switch. All nine amateur
>bands are
>> supported. Three decks are close spaced, and are wired in parallel
>for current
>> handling capability. The two additional decks are used to add C1 and
>C2
>> padding capacitance for 160m. The padders are the largest I have
>ever seen,
>> measuring 1.5 and 2 inches in diameter for C1 and C2, respectively.
>The output
>> tank circuit is a Pi-L with the output L an untapped 4:1 coaxial
>UNUN. This
>> transforms the image impedance of about 200 ohms to the 50 ohm
>output
>> impedance.
>> The RF choke is the largest I have seen on any amateur
>> amplifier, measuring about 7/8" diameter by 7" long on a
>> ceramic form. The plate blocking capacitor is neatly
>> fitted directly to the end of the RF choke, and is a 2700pF, 15KV
>component.
>> Plate tune and Load capacitors are large air variable, and driven
>with high
>> quality ball-bearing reduction drives from the front panel.
>> The 4CX1600B is housed in a huge ceramic chimney with a
>> Wall thickness of a half-inch. A parasitic suppressor connects the
>anode to
>> the plate choke/blocking capacitor. The tube is similar in shape and
>size to
>> an 8877.
>>
>> RF output Wiring
>> Teflon coax (RG-303) is used on all output wiring to the
>> QSK board which uses a Jennings RJ-1a vacuum relay for the
>> output. Full break-in operation is supported at full power
>> on all bands. A shielded and enclosed RF sensor is used
>> for the forward, reflected and SWR Fault detector.
>>
>> Operation
>> There is a 2-3 minute wait for warm up. The Ready LED does
>> not flash during warm-up, which would be a simple feature
>> to add, and one that is needed. As received, all LEDs are out during
>warm-up
>> until the timer has expired, then the ready LED comes on. The
>factory presets
>> for all nine bands were right on the mark. The amplifier puts out
>1,750 -
>> 1,875 watts on all bands with 60 watts of drive. With 50 watts of
>drive, the
>> amplifier is at 1,500 watts out.
>> If an incorrect antenna is chosen, the amplifier faults
>> immediately to bypass. I was not able to get the amplifier
>> to flash over in any circumstance with the wrong antenna
>> selected. Anything over about 2.5:1 kicks in the
>> protection circuit, a very nice feature. This feature will protect
>against
>> potentially significant RF deck damage in the event an antenna comes
>down, is
>> covered with ice, or is simply the wrong antenna for the band.
>Tuning is
>> simple, and similar to tuning a triode amplifier. After pre-sets are
>chosen,
>> apply 25 watts and peak the Load and tune. Slowly increase power,
>while
>> peaking the output, and watching the Ig2 LED's for screen grid
>current.
>> Slightly heavier loading keeps the Ig2 LEDs to one or two RED
>segments, which
>> represents about 20-25mA.
>> The amplifier will immediately fault to bypass of too much
>> input drive power is used. Both the SWR and Overdrive
>> faults are reset automatically in two seconds. If the fault
>> remains, the amplifier will not re-key. Observation on a scope of RF
>output
>> during QSK operation was perfect with both full and semi-break-in.
>>
>> Cooling
>> A high quality blower is used, and it moves a lot of air.
>> It appears to be a 220Vac 50Hz motor. At 60 Hz, it runs a bit too
>fast and has
>> a bit more high frequency white noise
>> Than I would prefer. It is run at about 120Vac in the normal mode,
>using a
>> primary tap on the transformer as an auto transformer (no neutral
>current on
>> the mains). There are temperature detectors in the tube chimney air
>flow that
>> will switch to 220Vac operation at about 100 Deg C. I never heard
>the blower
>> increase in speed. The tube runs very cool, with efficiencies in the
>65% range
>> on all bands, and cools very quickly after CW or tune operations.
>> Air flow in this amplifier is excellent for the tube, but
>> not as good for the other two items that need attention.
>> First, the tank components should have some air
>> Circulating by them, and the p/s diodes and bleeders should also be
>in the
>> intake air path. There is some intake air that flows by the p/s, but
>none
>> flows through the tank.
>> In this amplifier the tank components are so large, not
>> Much heat is generated in any of the tank components, except the #10
>ceramic
>> coil form, which does get warm. The P/S diodes are so large they
>also run
>> cool, but the bleeders and B(+)glitch resistors do get warm.
>> This is about the only area in the entire amp that I can
>> complain about, but realistically, even with RTTY operation
>> at 1,500 watts continuous, it would probably never be a
>> problem.
>>
>> PC Boards
>> Glass epoxy boards are used throughout, for the HV p/s,
>> Control board, Display board(s) and QSK. The HV p/s,
>> Control and Display boards are all replaceable with push pin
>connectors.
>> Should a replacement or upgrade be necessary, use of connector
>housings
>> (rather than individual pins)would greatly simplify that exchange.
>>
>> Metering
>> I chose the DX-2a version because I am partial to analog
>> meters. The digital version has the advantage of seeing
>> all five parameters at once, with no switching.
>> The meters uses are very nice, large bright white meters
>> with easy to read back-lit scales. One is fixed for plate
>> current, the other is switched for Forward Power,
>> Reflected Power and Plate Voltage.
>>
>> Ip = 1.5A f/s
>> Vp = 4KV f/s
>> Pf = 2KW f/s
>> Pr = 200W f/s
>>
>> There are several spare positions on the meter function
>> switch. I would like to see filament voltage added, since
>> it may vary with line voltage. Since this is a tetrode with a 350Vdc
>regulated
>> screen supply, it might be nice to read
>> that too. Screen Grid current is also metered with a 6 segment LED,
>reading
>> from neg 10mA to pos 35mA. The Ig2 LEDs are a great tuning aid, and
>make it a
>> very fast chore to peak the tune and load, while keeping the
>loading
>> sufficient to keep Ig2 below 25mA. At 35mA all four segments light,
>at greater
>> than 35mA they flash. This is one of the better tuning aids I have
>seen, and
>> is very intuitive to use.
>>
>> Documentation
>> The users manual is one of the most extensive of any
>> amplifier I have used. There are diagrams for linearity,
>> overdrive conditions, QSK timing, etc... Partial
>> Schematics are provided and the operation section is well written
>and
>> thorough. A pre-set chart is provided with factory settings
>included.
>>
>> Summary
>> While most US amplifiers have concentrated on cost
>> Reduction in recent years, it's a pleasant surprise to see quality
>improving
>> at a very fair price. This amplifier is a great value for the money
>(about
>> $3200 delivered with QSK). It is built with more expensive
>components than
>> most US amps selling for more money. Workmanship is excellent, and
>> Layout is modular and easily serviceable.
>> The performance is flawless, and the protection circuits
>> work well. You can not easily damage this amplifier, so
>> the user is protected from simple and common mistakes.
>>
>> A few recommendations to future revisions:
>> 1. Flash the Ready LED during warm-up;
>> 2. Duct the intake air by the tank components and P/S;
>> 3. Add a few more metering functions to the meter switch;
>> 4. Use AWG 14-3 SWOJ cordset;
>> 5. Add complete schematics and calibration/alignment
>> procedures;
>> 6. Add connector housings to the wiring harness for PC
>> board connectors.
>>
>> --
>> FAQ on WWW: http://www.contesting.com/ampfaq.html
>> Submissions: amps@contesting.com
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>> Problems: owner-amps@contesting.com
>> Search: http://www.contesting.com/km9p/search.htm
>
>
>
>
>--
>FAQ on WWW: http://www.contesting.com/ampfaq.html
>Submissions: amps@contesting.com
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>Problems: owner-amps@contesting.com
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>
>
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