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-----Original Message-----
From: John Devoldere (ON4UN) <john.devoldere@village.uunet.be>
To: dx-news@jerseycape.net <dx-news@jerseycape.net>; ham*topband
<Topband@contesting.com>; dx@qth.net <dx@qth.net>; ham*contest_announcements
<CQ-Contest@contesting.com>
Date: Monday, July 12, 1999 3:45 PM


One year of using the ACOM 2000 Automatic HF linear amplifier. (by John
Devoldere, ON4UN)


Early 1998 I was approached by Vasko, LZ1JK, to "life" test a new automatic
amplifier he had developed. I was happy to do so, especially after I found
out how unique this new amplifier really was. After 1 year of thorough
testing, it's time to share my experiences with my fellow amateurs.


ACOM may not yet be a well known name in the world of amateur radio
equipment, but no doubt soon will be. ACOM was the company which for many
years produced the Alpha 91b amplifier, the most popular of the Alpha (ETO)
amplifiers. The company not only produced that amplifier, they build it
almost exclusively with parts made in Bulgaria and other Eastern European
countries. This together with the lower labor cost as compared to the West
made it possible for Alpha to sell a top notch amplifier at an attractive
price. The Alpha 91 soon obtained the reputation of being every bit as good
as the more expensive amplifiers made in the USA. Through all the expertise
Vasko and his company acquired during the years of being a subcontractor for
Alpha, they gained all the knowledge which made them decide to develop an
amplifier of their own.

ACOM set out to develop a 1500 Watt (continuous duty!) output amplifier with
full autotune (not memory tune) features, using two GU74 (4CX800A) tubes by
Svetlana, the same as used in the Alpha 91 amplifier. You can find these
tubes new on the flea markets for typically 50 to 60$ (the 3CX800's used in
many US-made amplifiers cost at least 5 times as much). Their goal was to
make an improved version of the Alpha 87A "memory tune" amplifier, which is
considered by many to be the top of the range amplifier on the amateur
market.


The improvement turned out to be the fact that the ACOM is a true autotune
amplifier, while the Alpha 87A is in reality a memory-tune amplifier,
capable of memorizing two sets of tuning setting (per band segment), one for
nominally 50 Ohm and one for an impedance which must be pre-programmed by
the user through manual tuning.


The ACOM 2000 is the first real auto-tune amateur HF-amplifier I have seen.
By pressing a simple button on the remote control panel it fully
automatically tunes itself completely within about 0.5 seconds. The
auto-tune function is not limited to recalling preset values, it actually
tunes for a conjugate match for whatever load within the must be .." 2:1 SWR
circle on 160m and within the 3:1 circle on all other bands, and does that
fully automatically, with no human intervention at all. I have been queried
whether t his was achieved by using a built-in antenna tuner. No, the
matching is done with a classic Pi-L network, of which the tune capacitor,
the bandswitch and the load capacitor are driven by stepper motors,
controlled buy the logic from the logic control board. The amplifier has an
absolutely blank front panel (except for an AC on-off switch), which makes
it possible to "hide" the amplifier in any convenient place. All control and
monitoring functions are grouped on a small remote control box, which can
easily be positioned next to the keyboard during operation. The ACOM
amplifier can be connected via an RS232 connector to a PC for either remote
control or testing. It even has a built in processor that keeps track of all
the important data (currents, voltages, temperatures), and in case of a
breakdown you can down load the measured values via a modem to the factory
for further diagnosis.

The Acom 2000A amplifier tunes automatically (change band-switch, loading-C
and tuning-C) for any frequency between 1.8 MHz and 29.8 MHz. There is a
possibility to do manual tuning as well, but who would want to use that?
Settings of the Pi-L network components are memorized for the various band
segments. The width of the band segments depends on frequency: 1.8-2.2 MHz:
25 kHz, 2.2-5 MHz: 50 kHz, 5-15 MHz: 100 kHz, 15 to 21.9 MHz: 150 kHz, 21.9
to 22.5 MHz: 200 kHz, 22.5 to 26.5 MHz 250 kHz and above 26.5 MHz: 300 kHz.
In the Acom 2000A you can load into memory those presets values (obtained
through automatic tuning is less than 1 second) for up to 10 different
antennas (per band), each one having slightly different impedances, and that
for each of the band segments. This adds to a total of not less than 490
sets of pretune-values. The correct preset values, matching a particular
selected antenna can be recalled from the remote control panel (which band
section, which antenna). Alternatively one can use a computer program to
control this selection via the RS232 connector. The same program could also
control the antenna selection, making matching of antenna selection and
amplifier tuning full-proof. When used with the ACOM 2000S automatic antenna
selector and the ACOM 2000SW remote antenna switch, you are always 100% sure
that you have selected the correct setting for each of the antennas.


The workmanship of the amplifier is exactly the same as we know from the
Ahlpa amplifiers: it is perfect, in a class by itself.


The remote control unit (hardly larger than a calculator) has an
alphanumeric LCD display where you can read about any imaginable parameter
of this amplifier, including quite uncommon things like filament voltage and
current (separate for each tube) and tube cooling air outlet temperature!
You can measure anything you can imagine. A true luxury! When you switch on
the linear the display will tell you how long you have to wait until it is
all warmed up. No need to get nervous, you know exactly how many more second
you have to wait until it will play. An there will be no more time waiting
with tuning up. Just apply drive (on any band) and off you go!


At full output the amplifier runs very "cool" and you can hardly hear the
blowers (a squirrel cage blower for the tubes and a muffin fan blower for
the power supply). The ACOM 2000 can be pushed to the 2000 Watt output level
(depending on the exact mains voltage) and that for approx. 85 watts of
drive.


The amplifier automatically senses the driver RF signal, and switches to the
appropriate band segment after a band change on the exciter. To change bands
all you really need to do is sending a short dot, or say "a" ("b" is fine as
well) in phone, and the amplifiers will tune up in a fraction of a second.


Needles to say that the use of this amplifier has greatly increased the
flexibility and efficiency at the OTxT contest station. The amplifier has
been used in every contest since early June 1998, and has performed
flawlessly ever since: we have had not a single problem with it. It must be
said that Vasko did a really outstanding job! On your operating position,
you just put the remote control unit next to the computer keyboard, and off
you go. A pleasure to have and to operate! I have truly never experienced
anything like that in my whole radio amateur career.


The amplifier has a serial RS323 port for connection with a PC. Using a
suitable program, all functions of up to 15 amplifiers can be controlled
from the PC.


Inside the amplifier various microprocessors do various tasks. One of them
continuously monitors and logs all the measurement data (voltages, currents,
temperatures, settings of variable C's etc). In case of a failure (it never
occurred to me) you can connect the amplifier to a telephone line, and via a
built in modem, the relevant data will be down loaded to the factory service
center, where a the problem will easily be diagnosed. This too is a unique
approach in servicing amateur radio equipment!


ACOM has set an attractive end user price limit for all countries where the
amplifier is sold. It is without any doubt that the amplifier will be a well
selling product. The amplifier can easily be run at 1000 Watt output by
merely reducing the drive level. This is important for countries where 1500
Watt is not allowed,


The manual is extremely well done with lots of pictures and a schematic. A
service manual is available as well.


At this time ACOM is still setting up sales channels in different areas.
Potential US customers check www.hfpower.com (e-mail: info@acom-intl.com).
Outside the USA, contact ACOM at acom@aster.net for details on the current
distributors list.

By the way, tehre's a picture of the ACOM2000 in my shack on page 15-6 of my
new LOW BAND DX-ing book.

Ghent, July 10th, 1999




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