[Amps] Expert Amps 2K-FA: Any Opinions ?

Thu Apr 26 10:05:48 PDT 2012

Paul, yes, I have noticed a drop-off in output power with keying when 
operating at 1500W out in MAX mode.  The output drops by as much as 200W 
before leveling off.  Presumably, it is a temperature effect.  I'll 
monitor it more carefully in the future so I can provide a better 
description.

When operating in MID power mode with ALC control and about 1100W out, 
the output is quite steady.

I forgot to mention in yesterday's post that I have detected some RX 
"hash" when switching from STANDBY to OPERATE.  However, it's been 
inconsistent.  So I want to check it more thoroughly across all bands to 
make sure that it's not something else in the shack misbehaving.

73, Joe
K2XX

On 4/25/2012 12:13 PM, Paul Christensen wrote:
> Joe,
>
> Do you detect obvious output power change with changes in PA temperature?
> I see about a 10% reduction with the 1K, approaching 15% when the PA deck
> starts getting really heat stressed.  While operating in CW mode at 1500W,
> does the amp ever kick to the MID power setting?
>
> Paul, W9AC
>
> ----- Original Message -----
> From: "Joe Giacobello, K2XX"<k2xx at swva.net>
> To: "Paul Christensen"<w9ac at arrl.net>
> Cc:<amps at contesting.com>
> Sent: Wednesday, April 25, 2012 12:04 PM
> Subject: Re: [Amps] Expert Amps 2K-FA: Any Opinions ?
>
>
>> I've owned the 2K-FA since about the first week of 2012.  So far, I'm
>> quite happy with it. It replaced a TenTec Titan 425 and a Command
>> VHF-1200.  I was getting ready to contribute a write-up on it for the
>> Contesting.com site, but I wanted to evaluate it for a few more weeks
>> before doing so.  Here are some initial assessments.
>>
>> 1.
>>
>>     It easily puts out 1500W on all bands from 6-160M with about 30W
>>     drive.  I have seen the output power go as high as 2,200W out on
>>     some bands when running it in MAX power mode and allowing the ALC to
>>     limit the drive.  With 1500W out, you're limited to about 15 seconds
>>     or so key down and then it automatically switches to MID power
>>     mode.  (Power was measured with a fairly recently calibrated LP-100A.)
>>
>> 2.
>>
>>     Utilizing the ALC and maximum exciter drive (200W), as recommended
>>     by the manufacturer, in MID power mode, it puts out about 1,100W. The
>> ALC action throttles the drive to about 40W.  Presumably, the
>>     key down time under these conditions is quite long, since MID power
>>     is recommended for RTTY by the manufacturer.
>>
>> 3.
>>
>>     The amp is set up for connections to two different exciters and band
>>     switching can be accomplished automatically through parallel
>>     connections to the exciters' serial ports or via the amps internal
>>     frequency counter.  The manufacturer recommends using serial port
>>     switching rather than relying on the frequency counter.  Having all
>>     switching done internally in the amp has really simplified and
>>     reduced the number of coax links and external manual switches in the
>>     shack.  I think the exciters will also switch automatically with
>>     applied RF, but I've never tried it.
>>
>> 4.
>>
>>     The amp has a port for connection to a Steppir control box for
>>     automatic band selection on their antennas.  I haven't hooked this
>>     up yet.
>>
>> 5.
>>
>>     I have run 200W through the amp in standby mode without any
>>     problems.  However, because of the internal switching, the exciters
>>     are not connected to an antenna unless the amp is turned on.
>>
>> 6.
>>
>>     In contrast to its predecessor, the 1K-FA, fan noise is barely
>>     noticeable.
>>
>> 7.
>>
>>     The internal tuner seems to work as advertised, but I never use it
>>     since I have all resonant antennas or an external Matchbox.
>>
>> 8.
>>
>>     The only serious problem I've had is that one of the six antenna
>>     ports doesn't work at all.  The domestic distributor (Expert Amps
>>     USA) offered to fix it on the spot if I brought it with me to the
>>     Orlando Hamcation.  But since I could live without one of the ports,
>>     I decided not to bother.  In talking there with the owner and
>>     designer, Gianfranco I0JY, he thought it might be a relay.  (It also
>>     might be a cable problem, but I haven't gotten in there to check.)
>>
>> 9.
>>
>>     I don't operate RTTY or contests (seriously), so I've never seen the
>>     internal temperature exceed 50C.  I believe that the amp shuts down
>>     if the temperature gets to 76C.
>>
>> 10.
>>
>>     One problem that I have is that there is no service manual. Apparently,
>> the manufacturer is concerned about protecting his
>>     design.  (OTOH, it seems to me that it could be easily reverse
>>     engineered.)  Nevertheless, the service guru is a W5 who shows up on
>>     the reflector to answers questions, etc.
>>
>> I'm not sure that I understand Joe's (W4TV) comments regarding the antenna
>> issues when operating SO2R, but that's probably because I don't work
>> contests.
>>
>> The bottom line is that with the exception of the antenna port problem,
>> the unit has worked flawlessly so far.
>>
>> 73, Joe
>> K2XX
>>
>>
>> On 4/25/2012 9:57 AM, Paul Christensen wrote:
>>>> I would also be concerned about cooling (and noise) with that much
>>> dissipation in such a small box.
>>>
>>> I have the 1K version of the SPE amp.  Nice, compact and reliable design.
>>> If the League's QST product review is to believed, IMD performance is
>>> excellent for a solid-state design.
>>>
>>> No contesting here but when using CW in say....a 2-3 minute exchange, the
>>> PA
>>> deck becomes quite hot and the fans are running "full tilt," resulting in
>>> what sounds like a jet engine.  That, together with output power that
>>> changes with PA deck temperature seems to be problematic with most
>>> commercial solid-state amps.  SPE does use a very well designed
>>> protection
>>> system.  In effect, a high-speed bus is created to kill bias to the PA
>>> transistors when one of about a half-dozen faults occur.
>>>
>>> I like the amp for its instant-on, compact design, but I would never use
>>> it
>>> as a replacement for a good VT amp.  I saw the 2K amp recently at the
>>> Orlando hamfest and for folks wanting a solid-state amp, I think it's
>>> worth
>>> considering.  But if noise in the shack is bothersome issue, ask other
>>> owners about noise level with varying duty-cycle at full output power.
>>>
>>> I believe the 2K version has a vacuum relay option that adds several
>>> hundred
>>> dollars to the purchase price.  In my 1K, its T/R frame relays were way
>>> too
>>> loud.  I ended up modifying the amp's logic for use with an Ameritron
>>> QSK-5.
>>> The interface between the two units is optically isolated and a schematic
>>> is
>>> shown on my QRZ.com page.  Much happier with this arrangement as it's
>>> fast,
>>> silent, and no truncation of keyed elements.
>>>
>>> Paul, W9AC
>>>
>>>
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>>>
>>>
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