This post from the YCCC reflector might be of interest to you AMP types. The
first message is about the 3CX800. Could this, rather than parasitic
oscillations, be the real cause of thumps and bangs in 3XC800 amps? Have fun
with that debate! The second message is my review of the Acom 2000A vs the
Alpha 87A.
73, Dick WC1M
-----Original Message-----
From: yccc-admin@yccc.org [mailto:yccc-admin@yccc.org]On Behalf Of
Jordan, David
Sent: Thursday, December 19, 2002 8:56 AM
To: 'dick.green@valley.net'; Bob McCormick W1QA; yccc@yccc.org
Subject: RE: [YCCC] Which amp: Acom 2000A or Alpha 87A (very long!)
Just my 2 cents w/ regards for tubes.
When I designed 10KW amps art Harris RF, We used a pair of 3cx800's
for the dirver to the 3cx10,000 final. We also used 3 phase power supplies
to drive
this beast. Our number 1 problem was tube arc's. Bothe the 3cx800 and
3cx10,000
would constantly arc. The reason has top due with the physics behind the
tube designs.
They both suffer from to little plate current to support the plate power
Eimac designed the 3cx800 for Harris to use in our amps. They took several
designs
and combined them to get the 3cx800. The problem is that the plate
voltoltage and current
is a to great a multiplier above the filament current and voltage for that
type of tube design.
This gives to much energy from electron bombardment from the plate to the
grid. This eventually
dislogges enough of the of the grid metal to cloud the tube and create a
great path for tube to "ping"
or arc. It actually sputters inside the tube. Now in a 3 phase system,
where current never has a zero cross,
the short circuit only ends when the power supply or tube blows up. Yes
there are arc detection circuits
but they don't stop the arc they only limit the lenght of the arc.
Cumulative plate arc will destroy the tube over time.
Now most ham amplifiers are single phase and the current from the power
supply will have
zero crossings and extingish the arcs. The problem is still there and the
tube will self destruct over time.
You can add arc detection to the powersupply but that only saves the supply
and does not prevent Plate arcing.
In reality, the 3cx800 is nothing more than a beefed up 3cx400 base with an
3cx1000 or similar to the 8877 style plate.
The problem is that the grid design is not robust enough for the 800W style
Plate.
The 8877 is a far superior tube!
Just some history, Doesn't mean the amp wont work, but if you ever hear a
ping, you know what happened
and that you should consider ordering a spare set of tubes. That's the
signal it's time to place your
order.
And no, I dont have any 10KW amps or tubes
Dave, KC1Q
David Jordan, Pr. Antenna Engineer
> Automotive Telematics and Commercial Antenna
> M/A-COM, A tyco INTERNATIONAL LTD. COMPANY
> 1011 Pawtucket Blvd. Lowell, MA 01853, MS 158
> ph: 978-442-4190 fx: 978-442-5419
> jordand@tycoelectronics.com
> www.macom.com
>
>
> -----Original Message-----
> From: Dick Green [SMTP:dick.green@valley.net]
> Sent: Wednesday, December 18, 2002 10:21 PM
> To: Bob McCormick W1QA; yccc@yccc.org
> Subject: RE: [YCCC] Which amp: Acom 2000A or Alpha 87A (very long!)
>
> Bob,
>
> I use one of each in my SO2R station. Here are my thoughts:
>
> - They are both terrific amps -- well designed and very well built. I'm
> sure
> you would be happy with either one.
>
> - The designs are similar, although the 87A uses the Eimac 3CX800 and the
> 2000A uses the Svetlana 4CX800. The latter is much less expensive, but may
> have more reliability problems. More on the tubes below.
>
> - The 87A uses pin diode T/R switching, which is ultra fast and silent.
> The
> 2000A uses a Jennings-style vacuum relay, which is slower and generates a
> tiny bit of noise. More on the pin diodes and relay below.
>
> - The 87A is programmed to trip on SWR greater than 2:1, while the 2000A
> is
> more forgiving and easily handles SWR as high as 3:1. It's not clear why
> the
> 87A trip level is so low. I've heard that it's because the pin diodes
> can't
> take the reflected power, but I've also heard it claimed that other parts
> of
> the output network aren't beefy enough to handle the reflected power. The
> 87A's low trip point is definitely an annoyance. Unless you have very flat
> antennas or use a tuner, you will run into it.
>
> - The 87A blower is reasonably quiet - it sits on my desktop about three
> feet away from me. The 2000A blower is much quieter. It sits on the floor
> about five feet from where I sit and I can't hear it at all.
>
> - The 2000A has a remote control unit (RCU) that sits on the desk. It's
> about the size of a paperback book. The interface is excellent, easy to
> use
> and has great diagnostic information (text messages on an LCD screen.) The
> 87A has front-panel controls that are also easy to use, but the diagnostic
> display is primitive (LEDs).
>
> - On the other hand, the 87A has a better computer interface. You can hook
> a
> terminal or computer communication program to the RS232 interface and get
> good diagnostic info. It's not quite as complete and informative as the
> 2000A RCU, but it's more than adequate.
>
> - The 87A also has AlphaRemote, which is a simple control and diagnostic
> program for Windows. It takes the RS232 info and displays it on the CRT.
> It's a nice, easy program to use, but not terribly robust. There is a
> third-party control program called Acom Tools for the 2000A. It's OK, but
> kinda clunky to use. It has some interesting features, like the ability to
> automatically retune the amp based on a frequency entered in a program.
> There's an interface to the Writelog contest logging program for this.
> Writelog reads the frequency from the rig and sends it to the 2000A for
> retuning. Although both the 2000A and 87A have automatic retuning whenever
> you transmit, this feature allows retuning when you change the frequency
> on
> receive. Nice for retuning when you change bands for search-and-pounce.
>
> - This somewhat obscure feature is important for contesting with the
> 2000A,
> especially if you like to chase packet spots. That's because there's a
> major
> difference in the way the 2000A and 87A do their automatic retune. Both
> work
> such that if you send a dit or speak after changing the rig's frequency,
> the
> amp will automatically retune. The 87A will send the code element or
> speech
> at low power while retuning, but the 2000A shunts the input RF to a dummy
> load while switching. In other words, it's lost. So, if you change bands
> and
> then try to send your call to another station, there's a good chance with
> the 87A that the entire call will be heard at the other end. But with the
> 2000A, the first letter will be lost or clipped. If you use the Acom Tools
> control program and Writelog, the 2000A will retune when you change
> frequency on the rig (i.e., you don't have to transmit.) This way, nothing
> is lost the next time you transmit.
>
> - As you might imagine, chasing packet spots with these amps can be a lot
> of
> fun (provided you have Acom Tools and Writelog for the 2000A.) All you do
> is
> click on the spots and send your call. The amps retune automatically. I've
> gotten the rate up to well over 100/hr in phone contests doing this (I
> never
> use packet for CW contests.)
>
> - Speaking of tuning, the two amps are rather different in this regard.
> Both
> were originally designed to store tuning parameters for small band
> segments
> in memory. When setting up the amp, you select a desired antenna and tune
> it
> for each segment on each band. When RF at a particular frequency is
> detected, the amp selects the matching tuning parameters and uses stepper
> motors to retune the amp. The first difference is in setup. On the 87A,
> you
> do the tuning of each segment manually, using front panel TUNE and LOAD
> push
> buttons. There's a nice TUNE mode and procedure that makes this relatively
> quick and easy. When each segment is tuned, you push a couple of buttons
> to
> store the parameters in memory. The 2000A offers a more automatic way to
> preset tuning for each segment. You set the desired frequency on the rig,
> pick an antenna, select TUNE mode on the RCU and transmit about 20W of RF.
> The 2000A automatically optimizes tuning for the selected antenna on the
> selected frequency segment and stores the parameters in memory. Much
> faster
> and easier than the 87A and quite accurate. There's even a DOS program
> that
> will let you step through frequency bands for each antenna quickly or
> initiate an automatic sequence to tune the entire amateur HF spectrum.
>
> - It might sound like the 2000A is the winner in this department, but the
> 87A has something that may be even better -- dynamic tuning. Using a
> feature
> called AlphaMax, the 87A can automatically optimize tuning on the amp
> while
> you are transmitting. When you first setup the amp you go through the
> preset
> storage procedure outlined above. When you first transmit on a given
> frequency, the preset parameters are retrieved as normal. But thereafter
> the
> amp continually monitors the operating parameters and adjusts the tuning
> dynamically. This is especially useful if you have more than one antenna
> per
> band. When you switch antennas, any tuning differences are automatically
> made by AlphaMax. For more info, see my review of AlphaMax and AlphaRemote
> in the August 2000 issue of QST.
>
> - The 2000A doesn't have dynamic tuning, but it does allow you to store
> parameters for up to 10 antennas for each segment. So, if you have
> multiple
> antennas on a band, you do the preset storage procedure for each antenna
> in
> each segment (real fast and easy with the DOS program.) When changing
> antennas while operating, you simply hit a couple of buttons on the RCU to
> select the desired antenna parameters. Not quite as automatic as the 87A,
> but adequate.
>
> - Both amps have an optional automatic antenna switch controller. The
> 2000A
> also has a compatible remote relay switch box. The 87A DAS can switch a
> number of popular remote relay switches (e.g., Ameritron RCS-8.) When
> changing frequency, the amp instructs the switch to select the antenna for
> the appropriate band (87A) or band segment (2000A). This can be more of a
> hassle than a benefit if you have more than one antenna per band. An Acom
> user has built a device around the Basic Stamp chip that supposedly deals
> with this. I think it allows you to select the appropriate antenna from
> the
> PC. I don't have the Acom switch, so I have no experience with this mod. I
> got the Alpha DAS unit back when I got the 87A, but stopped using it when
> I
> built my SO2R setup. The DAS is not well designed for SO2R because the
> switch doesn't change antennas until you transmit or push a button on the
> DAS. In SO2R, you almost always want to change antennas when changing
> frequency on the rig, and most of the time that's to listen rather than
> transmit. The Acom switch has the same problem, unless used with the
> special
> Acom Tools and Writelog setup. For antenna switching I use TopTen band
> decoders, which are driven directly from my Yaesu rigs. Bottom line, I
> don't
> think amp-based antenna switching is the way to go: way too expensive and
> not well designed for contesting. Better to go with rig-based antenna
> switching, especially if you sometimes operate low power.
>
> - As I mentioned, the build quality of both amps is superb. Service is
> excellent from both companies. There was a time when it was a bit
> difficult
> to get info from Alpha, but that has changed. I've been able to make
> repairs
> to my 87A several times with help from the factory (it's seven+ years
> old.)
> I found a firmware bug a number of years ago and the factory helped me
> patch
> it (not sure if the 2000A has any patching capability.) I fixed a bad op
> amp
> on the low voltage supply that was making an IP current LED flicker
> annoyingly. I also replaced a pair of pin diodes that went bad after about
> six years. I'm pretty comfortable working inside the 87A. Service from
> Acom
> has been excellent and very fast. They have answered every question in
> great
> detail and are willing to help me work on the amp. Several times, the
> factory has sent me detailed instructions for troubleshooting and
> component
> replacement. I've had e-mail correspondence with their top engineer about
> the amp's programming sequences and have gotten incredibly detailed
> responses.
>
> - Svetlana tube failures are among the more common problems reported on
> the
> Acom reflector, but I haven't seen an excessive number. I had a bad tube
> when my 2000A was new. Krassy told me that the screens in these tubes are
> somewhat susceptible to damage in shipment. The replacement has been fine
> for a couple of years. Tube replacement for the 2000A is considerably more
> complicated than for the 87A. For the 87A, about the only difficult part
> is
> getting the chimney and parasitic suppressor out of the way and being
> careful not to bend the tube pins. Other than that, you just stick the new
> tube in the socket. For the 2000A, in addition to some tricky moves
> getting
> the chimney, parasitic suppressor and temperature sensor out of the way,
> the
> bias has to be readjusted to set the plate idling current. You have to
> remove both the top cover and front panel to do this. The task doesn't
> require any special equipment -- the amp's computer has a built in
> procedure
> and the display provides all the info you need. However, the procedure is
> not documented in the user manual. I got very detailed instructions direct
> from the factory voa e-mail. It's my impression that they did not design
> this amp to have the tubes replaced by the user. I think the procedure is
> the reason why Krassy prefers that you send the amp in for service, even
> when a problem is very likely to be caused by a bad tube. Krassy replaced
> my
> bad tube, so I haven't replaced a tube myself yet. If it has to be done in
> the future, I'll do it myself.
>
> - The Eimac tubes in my 87A are the factory originals -- 7 years old with
> a
> lot of miles on them. A couple of years ago, one of the tubes was causing
> a
> cathode current fault and I replaced it. After a contest or two, the amp
> started getting various faults -- blown fuses, arc faults, power supply
> voltage faults and so forth. The faults got more and more frequent, and I
> became quite worried that the HV or LV supply had a problem. Eventually, I
> started getting hard faults, which shut the amp down completely. Sometimes
> the amp would make it through warmup, sometimes not. To make a very long
> story short, I tore the amp apart and checked every component on the HV
> and
> LV boards. I found nothing wrong with them. At one point, the small fuse
> in
> the step-start circuit blew and I got suspicious that the HV was shorting.
> I
> removed the tubes and, to my surprise and chagrin, the faults stopped. The
> new tube was bad! My guess is that it had been slowly leaking, and the
> gradual buildup of air inside caused more and more arcs which got stronger
> and stronger. At times, the arcs were so fast that a fuse would blow
> before
> the CPU could catch the fault. I've seen faults like this do severe damage
> to amps, but the 87A physical and software protective measures prevented
> that. I reinstalled the old tube that I thought was bad, and the amp
> worked
> flawlessly. It's been back in the amp and working perfectly ever since. My
> guess is that the old tube had a pin that was not contacting the socket
> properly -- possibly caused when I removed the tube when fixing a
> different
> problem. By the way, when I was packing the faulty tube for return to
> Eimac,
> the bad tube rolled off the table and the cooling fins got badly bent. How
> would I convince Eimac that the tube had been bad before this happened? I
> explained the situation to Alpha and they sweet-talked Eimac into
> replacing
> the tube anyway. Whew. Nice service from Alpha on that one.
>
> - My 2000A had a Kilovac HC-1 vacuum relay when new, and it failed (locked
> up) after a month or so. The factory told me that this was due to a bad
> batch of Kilovac relays. I happened to have a Jennings RJ1A, which is an
> exact replacement, and the factory sent me very detailed instructions for
> replacement (the president of Acom handled this himself!) It wasn't
> terribly
> difficult to do. The Jennings has been fine. Acom later sent me a
> Russian-made relay which is still on the shelf. Note that the HC-1 tested
> OK on the bench after I got it out of the amp. There have been several
> reports of relay failures on the Acom reflector, two very recently. In one
> of those cases, it's a Russian relay that failed. This makes me suspicious
> that the failures could have something to do with the amp design -- maybe
> they're running the relay at too high a voltage or there's a stray
> magnetic
> field affecting the magnet inside the relay.
>
> - In theory, the vacuum relay could wear out if you do a *lot* of QSK. I'd
> say you would have to CQ in a lot of contests in QSK mode to do that. I
> never use QSK when CQing and rarely when S&Ping (too much noise!) But pin
> diodes don't guarantee a lifetime free of repairs: I had to replace a pair
> of pin diodes on my 87A and it was a little tricky.
>
> - Acom service might be a better choice for us New Englanders because the
> repair depot is in Massachusetts. The one time I had to send my amp back
> (to
> diagnose and fix what turned out to be a bad tube), Krassy sent someone to
> pick up the amp at a Boston hotel at which I happened to be attending a
> convention (I live in western NH). Krassy fixed the amp and delivered it
> back to me by the end of the day. Now that's service! Even if UPS had been
> used, shipping to Massachusetts is a lot better than shipping to Colorado.
> I've never had to send the 87A back to Alpha (knock on wood), but that's
> because I've been real stubborn about trying to diagnose and fix problems
> myself.
>
> - The 2000A has much better firmware and diagnostics than the 87A. Not
> surprising, since it was designed at least 10 years later. A number of
> times
> the 87A has reported faults that are way off the mark of what is actually
> happening. For example, I used to have a TS950SDX that put out
> leading-edge
> RF spikes of nearly 250W, which would cause the amp to fault. The 87A
> always
> reported a gain-too-low problem instead of an overdrive problem. That's
> because the firmware checked for abnormal gain before overdrive. Took me a
> long time to figure this out, and the factory confirmed the firmware
> problem
> (actually, Dick Ehrhorn did that on the Amps reflector!) My troubles
> diagnosing the tube arc resulted partly from misleading fault code
> reports.
> Since a tube arc can cause all sorts of havoc throughout the amp, I got
> all
> kinds of different fault messages. It's probable that these reporting
> problems are bugs that could be corrected, but my impression is that no
> changes have been made to the 87A firmware for many years. I think there's
> a
> lack of expertise at the factory. Even if they had it, there is no longer
> room in the firmware memory for enhancements and fixes. Actually, I
> believe
> only an interrupt-driven fault handler can correctly determine the cause
> of
> a fault. Without that, the timing sequence of multiple sensor alarms can't
> be known by the firmware. I'm not sure whether the 2000A is
> interrupt-driven, but the fault reporting I've seen so far has been 100%
> accurate.
>
> - For the 2000A, you have to be careful when using a rig that can put out
> 200W or more. The input circuitry is not rated this high, even when the
> amp
> is bypassing the rig RF directly to the antenna (both in standby mode and
> when the amp is shut off.) If the RCU is getting power, it will report the
> overdrive -- even if the amp is not running. Bottom line is that you can't
> use the full drive of a 200W rig even if you take the amp off line. I have
> an FT-1000D capable of 200W, so I use it with the 87A. I use an FT-1000MP
> with the Acom. I think this limitation is very unfortunate and probably
> the
> worst design flaw in the 2000A.
>
> - I almost always CQ on my 87A and S&P on the Acom. I certainly switch
> roles
> and CQ with the 2000A, but I tend to avoid this. Why? No good reason, I
> guess. Part of it is that my FT-1000D is much better for sorting out
> pileups
> and it's hooked up to the 87A (because of the <200W limit on the 2000A.)
> Also, the 87A is slightly quieter -- no relay noise to drive me crazy in
> the
> sleep-deprived wee hours. The 87A is a real workhorse -- I've put a lot of
> miles on it in the last seven years. I also feel somewhat more confident
> about repairing the 87A myself than the Acom. One dumb reason is that I
> have
> a spare 3CX800, but no spare 4CX800! The 87A's AlphaMax is convenient for
> dynamically retuning when I switch from a monobander to the tribander. I
> like that for the CQ radio, whereas I have a little more time to manually
> select the antenna tuning parameter on the 2000A RCU on the S&P radio.
>
> - The 87A is $455 more expensive. I'm sure that's due to the higher cost
> of
> Eimac tubes and higher labor cost in the U.S. Acom shipping to New
> England
> is probably cheaper, too.
>
> - Bottom line: As I said, you will probably be happy with either amp. If
> your antennas are under 2:1, you operate lots of QSK in contests, you have
> more than one antenna per band, and you don't mind spending more up front
> and more for replacement tubes, the 87A is a slightly better choice.
> Otherwise, the Acom is probably the better choice.
>
> I realize that I haven't made your choice any easier, but I hope this
> helps!
>
> 73, Dick WC1M
>
>
> > -----Original Message-----
> > From: yccc-admin@yccc.org [mailto:yccc-admin@yccc.org]On Behalf Of Bob
> > McCormick W1QA
> > Sent: Tuesday, December 17, 2002 4:44 PM
> > To: yccc@yccc.org
> > Subject: [YCCC] Which amp: Acom 2000A or Alpha 87A
> >
> >
> > OK ... we're sitting on the fence ...
> > looking for a high end amp with auto tune, etc.
> >
> > Down to Acom 2000A or Alpha 87A ...
> > read all the reviews and searched all
> > the web sites that can be read ...
> >
> > Use will be for occasional operation and a contest
> > here and there; don't expect to take it on any
> > DXpeditions, etc.
> >
> > Your feedback is appreciated ...
> > either to the list or directly to my email.
> >
> > Thanks!
> > Bob W1QA
> >
> >
>
> _______________________________________________
> YCCC Reflector
> yccc@yccc.org
> http://lists.contesting.com/mailman/listinfo/yccc
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