In my survey for more information on the Emtron DX-3 I stumbled into a posting
on the Amps reflector from KA1XO.
To my surprise the reply from VK2AOT could not be found in the Amps reflector
archive so I've asked VK2AOT to copy me.
For those interested in this subject and the full story please find the
original posting from VK2AOT below.
73, Dick Knol
Date: Sun, 07 Mar 2004 20:21:10 -0800
From: Emona Electronics <firstname.lastname@example.org>
Subject: Fwd: Re: [Amps] Emtron DX-3
Gentleman, I have no intention to enter into any polemics with this
particular message addressed to anybody concerned with Emtron DX-3 amplifiers.
My aim is to provide factual information, as well as some technical and
engineering aspects with which some members of this reflector have been ill
informed. You may have read the " MUD SLINGING" exercise, written by Mr. Hall
Mandel KA1XO on this reflector, for one and only one reason, to degrade the
good name and reputation, Emtron amplifiers enjoy. This was definitely not a
review, reviews are usually written by people who actually use an amplifier,
use it over a period under heavy contest condition, and observe its cons and
pros. A respectable reviewer is usually an experienced person with technical as
well as practical knowledge, intelligent and totally unbiased. Mr. Mandel's
statements about the Emtron DX-3 amplifier are totally untrue, false, and show
great lack of technical knowledge.
I believe, that, as a manufacturer as well as an active member of the
design team, I'm competent enough to make corrections to Mr. Mandel's
assumptions. My response is as follows.
You caught me at the hotel room computer. The EMTRON DX-3 review is
not on this machine. I will send it to you on Sunday night.
1. The EMTRON DX-series of amplifiers are experiencing a breakdown
where the plate current swings all the way to max and the 600 volt
fuses blow and there are no spare parts to fix them, or reasons why
According to the above statement, all Emtron amplifiers are
experiencing a breakdown as described above!
Now here is the truth: Recently our representative for North America DR.
Vince Carammata had an unusual problem with two DX-3 amplifiers, where after a
three minutes of warm up period or due to slight vibration, a considerable jump
in plate current blew the fuse. Luckily at the same time we had the same
problem with a DX-3 here in Australia. We investigated the problem, and found,
that after turning the amplifier on and after a certain but inconsistent time
period, the control grid to cathode resistance was dropping as the temperature
of the tube was rising. RESULT: FAULTY GU-78B tube. However, after doing some
further research and investigations, we have found the primary reason for tube
failure. We belive, that a little 2.2nF capacitor in the EBS conducted,
considerably reduced the bias, plate current increased and the fuse blew. As we
have never paid much attention to the little in our opinion unimportant
coupling capacitor, which job is only to deliver some RF to gener
ate EBS voltage, we did not realize that some transceivers generate a
considerable high voltage spike, which could damage this capacitor, or even the
input coupling capacitor, and a loss of bias would occur. Hence, high plate
current and a blown fuse.
We had a second but exactly the same problem with a DX-2SP which we
brought back from Texas. Here the GU-84B tube was faulty and presented the same
symptoms as the GU-78B in the DX-3 amp. I immediately advised Vince of the
Out of several hundred Emtron amplifiers operating on all six continents, we
have so far replaced five tubes, three GU-78b, and two GU-84B. I'm still
waiting to see what Vince will tell me about the two amps he is servicing.
Gentleman, with a record like this, any manufacturer would be extremely proud.
And the reason for this fine record is not only the high quality of the tubes
used in Emtron amplifiers, it is also the design and the sophisticated
protection circuitry used in all Emtron amplifiers. An operator using an Emtron
amplifier can be blind, stupid and dumb, and will not be able to destroy the
amp, unless using a hammer!
2. There are ten amplifiers that have recently failed this way waiting
in Virginia, and they are going to be returned to their owners when
ex-Emtron repair person receives money to ship them back without
Well Mr. Mandel, if you can give me not ten, but only five serial
numbers of the faulty, fuse blowing EMTRON DX-3 amplifiers, I'm willing to give
you a brand new DX-3 or equivalent in cash! I have no problem putting my money
where my mouth is!! Are you???
3. The nomenclature on small electronic devices in the DX-series
been systematically erased and sanded off to prevent duplication of
the boards or
non-authorized repairs or redesigns from being done.
You are again talking in plural! There is one and only one electronic
device, where we have erased the nomenclature, and I give no apologies to
anyone! All manufacturers do it in one way or the other. We at Emtron have
spent many thousands of dollars on R&D, and we have full right to protect our
work, our ideas and our designs. We are actually talking here about the little
"ramp function driven soft start module"! Yes, the Emtron soft start unit is
really unique. As we all know, there are three different methods of soft
starting an Amplifier.
a.) The very old and relatively effective resistor / relay method,
used by many amplifier manufacturers. This method is good, but usually does
not allow using one single transformer if one wants to prolong the life of the
tube filament. The switching time is in many cases too short. However, this
depends on many factors, such as: the size of the transformer, tubes used,
filtering system, etc.
b.) The second and most ineffective soft start method certainly is
the so called solid state zero crossing method. That means, that the power is
turned on when voltage across the load is zero, but in a 50Hz system, it takes
only 5 miliseconds for the voltage or current to reach its maximum. 5
milliseconds is practically as good as a short circuit, and in most European
homes fuses blow! At 60Hz it's even worse.
c.) Now let's look at the Emtron method. In short, an IC ramp
function generator drives a 40Amp triac, connected in series with the load. The
circuit can be factory adjusted over a time span of say 1 to 5 sec. I can not
in this small space talk about many advantages of this system, for more info,
see Emtron WEB site. However, I feel quite comfortable claiming that this is
the best system under the sun. If I'm wrong, please accept my apology.
4. The schematic diagram appearing in the owners manuals is tacitally
Yes, this I do believe. We at Emtron do not just turn the handle, we
are continuously searching for better ideas, better designs and improved
performance. Just look at an Emtron amplifier build some three years ago and
one build today. You will see the difference! It is therefore very hard to
continuously upgrade the literature, specially if there is only a small not
very important modification. I know of manufacturers who for 15 years or more
have not made any improvements on their current models. Could be, that their
products designed so many years ago were so advanced, that no upgrading was
ever necessary, or they love turning the handle of their sausage machine! I
would certainly think of the latter.
5. The American Repair facility has been waiting for over one year for
Please give me some more details. I'm not aware of anybody whose
amplifier is waiting a whole year for service. Would appreciate your help. I
admit that sometimes I was perhaps a bit slag, or I have forgotten, after all
we are all humans. We do have a couple of the very original DX-2 amps with the
4CX1600B, where the tubes are faulty, new tubes are not available and we have
designed a new RF tube module with two GU-74B tubes which directly replaces the
4CX1600B module. At least we are doing something, we try to look after our
customers in the best possible way.
6. The Russian doorknob capacitors are KVI-3 and are not rated for RF
and may heat up, short circuit and explode with no warning.
A very interesting statement, partially correct but not in this
context. There are two types of Russian ceramic transmitting capacitors
available. The K15U-1 M1500 and the KVI-3!
The K15U are designed for all kinds of RF applications and very
suitable for tuned circuits as well, and if the voltage rating is right, they
are just perfect. There is nothing better!!
Now let's see the KVI-3. This capacitor has been designed for several
RF and pulse applications, but they are not suitable for high power, in high Q
tuning circuits. However, they are very suitable for RF coupling, de-coupling
and pulse work. We must remember that a capacitor used in pulse circuitry,
would usually for short pulse durations handle at least ten times the current
it was originally designed for. I'm talking here currents not voltages. This
capacitors are usually 10 or 20 kV devices.
Emton is utilizing these fine capacitors as a plate coupling
capacitor, where due to relatively high impedance, and not being part of the
plate tuned circuit (some people might argue about this), the RF plate current
is relatively low. We have tested this capacitor in a DX-4 with 5KW PEP, and it
wouldn't even blink. Not once has this capacitor let us down.
7. The exhaust pulling fan is half the CFM capacity of the pusher fan and
the buildup of
residual air pressure in the final tube plenum means a drastic loss
of tube cooling
air flow at best and a destroyed output tube at worst.
This statement is absolutely wrong. Let's have a good look at
DX-3/DX2-SP cooling system. We use a 72CFM turbine blower as the main unit to
pressurize the sub-chassis and push the air through the tube. Due to the air
resistance in the tube, the output pressure has been considerably reduced. It
has been found that due to the relatively small air inlet area of the tube
socked and the cooling area of the tube anode, under very heavy duty cycle, the
amplifiers sensitive temperature control would bypass the amp when it gets too
hot. By adding an additional exhaust pulling fan, which does not have to have
the capacity of the pusher blower was added. During our tests, it has been
shown that the actual anode body temperature was reduced by about 35degrees
Celsius. If the author of the "mud slinging statements" would just do a simple
test, to place the hand over the exhaust outlet with the engaged or disengaged
(and removed) pulling fan, he would never make a totally stupi
d statement #7 above. As far as I know, Alpha has been providing an optional
puling fan system for years, did anybody complain??
8. The tube sockets are manufactured in the mid 1960's. The tube itself
test amplifier was manufactured in 1990. The manufacturer does not
the amplifiers are "used" or "recycled" at any point and this is a
I have E.F. JOHNSON CAT. NO 122-0275, 3-500Z tube sockets also manufactured
in the 60's and have been selling them to an amplifier manufacturer, may I ask
what is wrong with sockets made in the 60's ? Tubes manufactured in the 90's
are new tubes, never been used before (also called New Old Stock - NOS). Some
Eimac tubes, manufactured some twenty years ago, are still sold as brand new by
some outlet. What would you call an amplifier using a brand new tube which was
manufactured some ten years ago a "RECYCLED AMPLIFIER"???
9. If the vacuum relay burns out it will be necessary to remove the
controller board. No
spare controller boards are available if the board is damaged.
You obviously are not very observant! The vacuum relay or the QSK
module is one of the easiest modules to remove. It is held in position with one
only M4 screw! By un- soldering the output coax and removing the screw, the
module can be removed with two fingers.
Re control boards, another total nonsense! We have at the moment 50
control boards in stock, and 200pcs on the way. In the early stages we had two
components which failed some times. Now the control board no longer fails, and
is the most reliable module in the amplifier. We do not sell spare control
boards, but they are available as a replacement, that means, you send us the
old or damaged board, and we will replace it with a new one. The same goes for
all Emtron amplifier modules.
10. The GU-78b tube is no longer being manufactured and when stock is
amplifiers will not have any source of substitute devices.
When corresponding with the factory in the mid 90's, the tubes were
manufactured periodically (every two / three years) in batches, according to
demand. There are still many military installations which require new tubes,
this is the reason, why GU-74B, GU-78B, GU-84B and many others are available.
All these tubes are minimum five years old, but brand new.
N.B. Please contact me here in Australia for any further info. I sincerely
believe, that the DX-3 amplifier is the one and only one in the world, and that
there is no better amp, that could meet the DX-3 in craftsmanship, features,
design, performance and price. There is world wide a silent majority of very
happy DX-3 users, who wouldn't even think of using any other amplifier.
73, Rudi ..VK2AOT
Please note, I will not enter any further discussions about this subject on
Please contact me if you require further facts about the EMTRON DX-3.
On Fri, 27 Feb 2004 09:59:24 +0100 "Mark Demeuleneere" <email@example.com>
> I'm about to change my trusted LK-800 for a new amp. My eyes fell on
> DX-3 from Emtron.
> Would appreciate some input from Emtron amp owners. Plus points,
> Kindly reply to me privately, will post excerpt summary without call
> 73 - Mark
> Stories and pictures on ON4WW's travels are on the following URLs :
> http://www.qsl.net/on4ww and http://users.pandora.be/on4ww
> Amps mailing list
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