ACOM 2000A

One Year of Using the ACOM 2000 Automatic HF Linear Amplifier

By John Devoldere, ON4UN

ON4UN_256.jpg (39245 bytes) Early in 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 one 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 91b 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 2000A Top View 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 91b 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 five 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 this 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.

ACOM2000SW_1.JPG (28117 bytes) 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 preset values (obtained through automatic tuning in 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. ACOM 2000S Antenna Selector 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 fool-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 Alpha 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. And 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 send a short dot, or say "a" ("b" is fine as well) in phone, and the amplifier will tune up in a fraction of a second.

Needless 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 RS232 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 Watts output by merely reducing the drive level. This is important for countries where 1500 Watts 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 can get more info on the web. Check:
http://www.hfpower.com/ or e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it ).

Outside the USA, contact ACOM at This e-mail address is being protected from spambots. You need JavaScript enabled to view it for details on the current distributors list.

Ghent, July 10^th, 1999

The ACOM 2000 Amplifier By Barry Kutner, W2UP

[excerpted from the FRC Newsletter August 1999]

As one who typically operates single-op assisted in the major contests, I'm always looking at ways to jump on those packet spots more quickly, and get in and out of the "packet pileups" before they get too big. Hitting Alt-F4, while running CT or Writelog takes the transceiver where it belongs. Antenna switching is handled by Top Ten Devices boxes. And then there's the amplifier... I've used a variety over the years: SB-220, Alpha 77, and Alpha 78 (bandpass tuning was a step in the right direction, but still too slow). For several years I considered getting an Alpha 87A, but I heard too many stories about it faulting out when the match wasn't perfect. While at N3RS last year for one of the contests, I saw an antenna tuner in their 20m stack line, just so the 87A would operate without kicking out. That clinched it - no 87A for me. So now what?

One day while Web surfing, I came across a site in Europe selling an amp called an Acom 2000A. It looked like quite an amp from the specs - full power using 2 Svetlana 4CX800A tubes, autotune(!) accepting up to 3:1 SWR (!!), and very high tech (more later). So how come I never heard of it? After asking around, I found a few things: it was pretty new, there were none in the US, and it was made in Bulgaria by the same company that made the Alpha 91B. So who had one? ON4UN had an early prototype. PY5EG, 4X1AD, and GW3YDX each had one. I e-mailed each of these guys with lots of questions, and they all answered with nothing but praise for it (isn't the Internet great?!) including "the best amp I ever owned." To make a long story short, I bought one.

The amp itself is a black box with only an on/off switch. All metering and controls are on the RCU (Remote Control Unit), which is a 7x5x1 inch box with LED bar power (fwd and refl) meters, several status LEDs, an alphanumeric LCD display, and a bunch of membrane-buttons to control the menu functions. The RCU comes on a 9 foot cable, so the amp (all 80 pounds of it) can be placed off the operating desk, out of the way. Very slick!

Setup and operation is a breeze. If you're the type that doesn't like reading manuals, which is very well written, considering it originated in Bulgaria, just turn the amp on (at which time you will hear TEST in CW), watch the 2 1/2 minute warm-up countdown, and start operating. The amp senses your operating frequency with the first CW dit (a single dit at up to 40 WPM, per specs), or voice syllable, and autotunes to factory default settings. The bands from 160-10m are broken down into segments (as small as 25 KHz on 160 and as large as 300 Khz on 10m). Each band segment has a factory default tuning setting, plus 10 user-customizable settings per frequency segment. This allows you to select more than one tune setting per segment, for use with alternate antennas, partial stacks, etc. where the load differs from your primary antenna. It's completely hands-off operation! However, you'll probably want to customize the tuning for your antennas. This is done via an auto-tune menu. You select the antenna number. Choose auto-tune, press the ENTER button twice, and the LCD display prompts with "Apply drive 10-20 W," with a small bar graph to help you adjust the exciter drive. The amp then autotunes for that segment (and antenna selection) in about 2 seconds. Do this for each frequency segment you operate and you're set for life, or until you install new antennas. It is now stored in memory, and is recalled in less than 1/2 second with that single dit at 40 WPM. Should you ever want to manually tune (though I can't imagine why), it can be done via the manual tune submenu. The measure submenu allows you to monitor 2 of 20 amplifier parameters at the same time, such as exhaust airflow temperature from each tube, filament current, power gain, line voltage, last frequency used, and more, plus all the usual things. But, there's really no need to monitor anything!

These guys have thought of everything. For example, line voltages can be set on the transformer for 100, 120, 200, 220, and 240 VAC. Not fine enough control for you? Via a submenu on the RCU you can set it for "high" or "low" with respect to the transformer tap for additional fine tuning. Personally, mine is set for high, as my line voltage runs 252V (yes, I've talked to PECO about it). A HELP submenu contains info such as software revision number, tube serial numbers, and actual operating time in hours, plus various tips. There is an INFO submenu selection. This transmits remote diagnostics over the telephone via audio Baudot RTTY generated through the RCU. Diagnostics are also available via an RS-232 port on the amp. Here's one for the esoteric department: You like the amp so much you own more than one. How does remote control software tell the amps apart? Each one can have a unique network ID! You don't want your son or XYL using the amp. It can be password protected via the RCU. Finished operating? Turn the amp off and it sends a CW "AR" to you.

You probably can tell I like this amp. I'm just waiting for the contest season so I can be in and out of the packet pileups before you guys get there! BTW, the amp is now sold in the US by Acom International in MA. You can find their Web page with additional info at http://www.hfpower.com/.

73 Barry

Excellent Amp. Well constructed, K6ANP

K6ANP	Rating: 5/5	Jul 16, 2001 23:15
Excellent Amp. Well constructed			Time owned: 6 to 12 months
It is the best amp I've ever owned. It is very easy to setup and operate. I ordered the 2000S remote switch with it. The combination can't be beat. Changing band and antenna is automatic. Late in the contest when fatique sets in and changing bands while forgetting to switch antenna can happen. The A2000 amp and switch combo removes the potential. Construction and quality is excellent. All critical measurements are monitored and if any are out of limits the amp automatically switches to standby. The best feature is the built in automatic antenna tuner. The second best feature is that the amp sits on the floor away from the top of the operating position. The remote control unit roughly 5"X 6.5" is the only thing that takes up operating space. The amp is very quiet even during contesting the blowers do not increase speed emulating the sound of a 707 during take off. I would recomend the amp without hesitation.

What a GREAT Company to deal with, WA7AW

WA7AW	Rating: 5/5	Dec 26, 1999 00:09
What a GREAT Company to deal with			Time owned: unknown months
Acom 2000-A is a piece of cake to operate and hook up. Mine had a fuse that was bad, simple troubleshooting led me straight to the prob. was easy to fix. what other company do you know that sends out Xmas Cards to their customers. email responses take less than a day in most cases. and last but by no means least...when was the last time a company GAVE an update to you FREE of charge, without requesting it or even charging postage. i do have one little complaint though. to change the internal fuses you have to unbolt and move the massive transformer out of the way to get to some of the fuses. all in all I am VERY satisfied with this unit and can recommend it to anyone who is looking for the newest tech in amp design wa7aw John

ACOM beats 87A hands down! , K1IR

K1IR	Rating: 5/5	Sep 3, 1999 13:02
ACOM beats 87A hands down!			Time owned: unknown months
Better on every dimension . . . Faster, simpler tuning. Handles REAL SWR situations (up to 3:1)! Super solid construction. Remote diagnostics. Remote control head gets the big box off the desk. RS232 controllable. Designed as part of a fully automatic system solution. Better price! The moment I saw this amp I was sold. I've been using one for several months, and I'll never go back to older technologies. Go to the ACOM website - http://www.hfpower.com - for more info on this outstanding amp. 73, Jim K1IR