Expert 2K-FA amplifier with Flex-6700?

  • 1
  • Question
  • Updated 4 years ago
  • Answered
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
Photo of Mike - N1MD

Mike - N1MD

  • 90 Posts
  • 3 Reply Likes
  • curious

Posted 4 years ago

  • 1
Photo of Sergey, R5AU

Sergey, R5AU

  • 842 Posts
  • 110 Reply Likes
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:  
https://community.flexradio.com/flexradio/topics/expert_2k_fa
https://community.flexradio.com/flexradio/topics/alc_with_expert_2k_fa
will be helpful
welcome on board of 2k-fa users
(Edited)
Photo of Jim Hawkins / K2JHV

Jim Hawkins / K2JHV

  • 28 Posts
  • 8 Reply Likes
Mike,

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.
Photo of WBB

WBB

  • 35 Posts
  • 4 Reply Likes
OM2500A works well
Photo of np2g

np2g

  • 271 Posts
  • 30 Reply Likes
OM4000A works better
Photo of KY6LA - Howard

KY6LA - Howard, Elmer

  • 3543 Posts
  • 1400 Reply Likes
BUT it uses Noisy Hot Expensive Tubes...
Photo of np2g

np2g

  • 271 Posts
  • 30 Reply Likes
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
Photo of WBB

WBB

  • 35 Posts
  • 4 Reply Likes
Yea ur right ... LOL
Photo of KY6LA - Howard

KY6LA - Howard, Elmer

  • 3543 Posts
  • 1400 Reply Likes
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
Photo of np2g

np2g

  • 271 Posts
  • 30 Reply Likes
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.
Photo of Sergey, R5AU

Sergey, R5AU

  • 842 Posts
  • 110 Reply Likes
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 - ?
(Edited)
Photo of np2g

np2g

  • 271 Posts
  • 30 Reply Likes
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 . 
Photo of Sergey, R5AU

Sergey, R5AU

  • 842 Posts
  • 110 Reply Likes
"Then the issue you hear  with the solid state amps becomes mute " agree, the noise is a point
but
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
(Edited)
Photo of np2g

np2g

  • 271 Posts
  • 30 Reply Likes
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) 
Photo of Sergey, R5AU

Sergey, R5AU

  • 842 Posts
  • 110 Reply Likes
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. :-)
(Edited)
Photo of np2g

np2g

  • 271 Posts
  • 30 Reply Likes
WOW thank you for the photo post . the  amp now has its big brother sitting there HI . 
Photo of Mike - N8MSA

Mike - N8MSA

  • 28 Posts
  • 19 Reply Likes
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.