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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.=20
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.=20
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.=20
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.=20
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.=20
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.=20
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.=20
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,=20
The manual is extremely well done with lots of pictures and a schematic. =
A service manual is available as well.=20
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=20
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