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Expert 2K-FA amplifier with Flex-6700?

Mike - N1MD
Mike - N1MD Member ✭✭
edited April 2019 in SmartSDR for Windows
I am very close to ordering this amplifier to use with my Flex-6000 radios. I am presently using an Elecraft KPA500 with the KAT tuner. It is great with the Flex but I am looking for a legal limit amp.

I have reviewed all the posts from the last several months and am wondering how all of you that are using the amp now feel about the device after several months of on-air use?

Does it follow the radio easily? How efficient is the auto tuner? How do you find the quality of the signal on all the modes? Is making a cable to interface the radio with the amp vial DDUTIL passive listener still the best way to go? Is it forgiving of operator errors? Anything I should beware of?

I have a Flex-6300 in addition to the 6700 and the ability to have two radio inputs is a plus.

Thanks in advance for your advice and experience.

Mike, N1MD

Completed · Last Updated


  • Sergey R5AU
    Sergey R5AU Sergey Member ✭✭
    edited April 2017
    Hi Mike,
    just finished today LZ CW DX :    F6700 +2k-FA +N1MM (S02V)+2 instance of skimmer
    no problem:
    - fully protected amp
    - tuner works excellent
     - IMD around -35 with my F6700 (Flex power out ~30watts (output power limited due to the regulations)
    - for 1,5kwt out you will have no visible problems even with 3-4 QSO per minute
    - for Digital you can use half mode power continuously (~1,1-1,2 kWt) or in MAX mode with limit
    input with 1,2 kWt out 
    - you know blower it is blowers - 4pcs on back panel +1pcs in power supply + 1 in ATU, even in case usage in the flat  - no big issues with noise

    pls visit also to related topics:  
    will be helpful
    welcome on board of 2k-fa users

  • Jim Hawkins / K2JHV
    edited April 2019

    I can't put it better than Sergey.  It's a wonderful amp and very quiet.  The fans modulate with power, but are still very quiet.  The tuner is also a huge benefit, even when you are running barefoot.  With the tuning table, you can pre-tune bands like 75/80 meters and just move around.

    Very little heat.  It is very forgiving.  The protection works perfectly.  I also moved from the KPA500, which is also a very nice amp.  I am going to keep the KPA as a backup.  I drive it with the Flex-6500.  I also like the peak power numerical readout for easy power control.  I've also used it for AM from the Flex, usually setting it to about 300W carrier.  I usually run wide 4.5K on 14.178 or thereabouts.  I run it on LOW power on digital.  You can inhibit bands that you do not use and set the output to up to 6 selections.

    So, no problem with the 2K-FA so far.  I've had mine for a few months.

  • WBB
    WBB Member
    edited November 2016
    OM2500A works well
  • np2g
    np2g Member
    edited January 2017
    OM4000A works better
  • WBB
    WBB Member
    edited April 2019
    Yea ur right ... LOL
  • KY6LA_Howard
    KY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited January 2017
    Sergey summed it up very well...

    Simple Answer - Superb solid state AMP with my 6700

    I usually get "Strongest Signal we have heard all day"  from DX and during contests.

    Because its instant on, I only turn it on when I need it so the blowers are not an issue.

    I actually bought it so I could run it with my 6700 while remoting as I can easily operate it (including turning it on and off) via software..

    Yes it follows the radio very easily through the passive listener in DDUTIL

    HOWEVER.. its totally autotune...so just click you mike or key once and it follows the radio frequency automatically

    My only caveat is that we are still trying to get the API from SPE so that Steve can integrate it directly into DDUTIL like he did with the 1K

  • KY6LA_Howard
    KY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited December 2014
    BUT it uses Noisy Hot Expensive Tubes...
  • np2g
    np2g Member
    edited November 2015
    Fu,s. No very reasonable. Have 5sets earmarked should last for by forever. And with 2holes. Hi. Well the fan noise wasn't bothersome with the om2500a. And the om 4000a is less
  • np2g
    np2g Member
    edited November 2015
    I have found the solid state amps still produce more distortion than any tube amp. Running ESSB. Yes you can hear that distortion. I don't care about instant on just power and a clean signal. What I have found out is when you introduce a amp that has headroom. That 1.5 kw level brightens up with. An amp not being pushed to its limit . And using the amp in a audio saturated environment the duty cycle really kicks up So when low watts out of your transceiver equals that kw. It's even better . Until we make a solid state amp that can Do. That I'm sticking with tube amps.
  • Sergey R5AU
    Sergey R5AU Sergey Member ✭✭
    edited April 2017
    Sound strange:

    2K-FA:  http://www.radio-ham.eu/eng/2kfa/scheda.html
                  3rd order distortion (two tone test) 36 dB typ

    OM2500A: http://www.om-power.com/om2500a
                   Intermodulation distortion:32 dB below nominal output

    IMD with level -36 is very good result, BTW -32 - -34 дб are very usual for GU-84b

    the question in backgroung is: which level of the IMD should be in you TRCVR in case usage this AMP ?  Predistortions - ?
  • np2g
    np2g Member
    edited November 2015
    it,s IMD within the pass band that is the issue . The low voltage solid state amps  are bad . higher voltage ones are better but still not as good as the tube ones.

    Having the below listed units :
     The GU84's are great when running AB1 at the correct idle current.(Bias)  The FU728s ones are better yet. (Tetrodes my friend) . 

    In this venue I have always supported Pre distortion  or clear signal  this is the absolute best way to produce a clean IMD representation from your Flex radio . 

    Some day this should happen . When it does -40 , -50 , -60 dbm  can be attained . And hooked up as to include that amplifier  Well it is fantastic. 

    This is IMD within the bandpass which flex and others produce  . 

    Then the issue you hear  with the solid state amps becomes mute . 

  • Sergey R5AU
    Sergey R5AU Sergey Member ✭✭
    edited April 2017
    "Then the issue you hear  with the solid state amps becomes mute " agree, the noise is a point
    In case looking for the silent environment  - tube AMP is right choise, however my selection is Solid State - i "tired" to use several kV on anode in flat, dynatron effect etc with tubes and wanna to have device in couple seconds ready and without any  negatives with lost electricity in outlet  - IMHO

    from my practics(since 1992), reality looks like:  

    below 1kWt - Solid state 
    over 1 kWt - Tubes

    even for now

    But in any way i am supporting pre-distortion concept and any steps forward with decreasing level of IMD, in case observe the HAM bands now, usual IMD what we can see between -20 and -30

  • np2g
    np2g Member
    edited November 2015
    I think we are approximately saying the same thing 

    Please Excuse me for not defining that mute comment.
    It is not environmental noise (Fan  etc.) it is the mixing of your audio products within the flex radio (Any radio) that produce or will produce  IMD .  The lower this is reproduced  IE : -30  -35   -40  -50  -60  the better or cleaner the output.

    And the cleaner the output from your exciter the better chance that your amplifier reproduces less of this garbage.

    So it gives a poor amplifier a cleaner signal and a great amplifier a better signal (Clear  clean,  or less  persuadable distortion.)

    And so far the low voltage solid state amps reproduce more of this garbage than tube amplifiers  . 
    If you talk with any of the hams that are really using ESSB  they all will relate the sad fact of the solid state amp. (So far) 

  • Sergey R5AU
    Sergey R5AU Sergey Member ✭✭
    edited April 2017
    Ed, agreed completely, 
    so, tube choise is important as well, to achieve -40 with Gu-84b:
    - correct idle current  - is individual for each tube
    - drive grid current  = 0 
    - very HIGH stability level of the voltage on the second grid  (on anode if possible too)

    i think -40 is very nice result

    however nice pic. with OM amp. :-)
  • Mike - N8MSA
    Mike - N8MSA Member
    edited February 2017
    I have a 2K that I use with my 6700. Works very well...

    Both the OM Power 2500A and the SPE Expert were tested by the ARRL, and both were found to have 3rd-order IMD -36dB below full rated output. This is consistent with what I see on my shack test gear.
  • np2g
    np2g Member
    edited November 2015
    WOW thank you for the photo post . the  amp now has its big brother sitting there HI . 

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