Sounds good to me - but at 3 months salary a little steep!! Oh well I
guess you have to pay for good quality rf items these days.
John ZS5JF
----------
> From: Andy Wallace <andywallace@home.com>
> To: K1WPO@aol.com
> Cc: amps@contesting.com
> Subject: Re: [AMPS] Operating comments using the Emtron DX-2a
To: <amps@contesting.com>
> Date: 31 January 1999 06:14
>
>
> Carl--
>
> Is this a good amp? Or does it need all sorts of "mods" to work
properly?
>
> Andy K5VM
>
> 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.
> >
> > --
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> > Problems: owner-amps@contesting.com
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>
>
>
>
> --
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