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Praise for Flex 6400M interface with Elecraft KPA500?

WayneWayne Member ✭✭

Thank you Flex Radio for an easy Plug N Play interface with my Amp ... (PRAISE)

The interface with the 6400M series to my KPA500 went flawlessly ...

Totally plug and play. Plugged key cable from TX1 jack to Key input on Amp. Set 20 ms delay in  the RCA TX1: Box where 0 was and  Set TX1 Enabled and all others RCA TX2-RCA TX3 as Disabled. Saved with word Amp in transmit profile after setting power levels on all bands to 30 watts which gives me 480 watts out but 35 will do 560 watts, the amp doesn't even flinch, actually it will do up to 640 watts without complaining.

Best amp I every owned. Yes its expensive but you get what you pay for (PRAISE - Isnt that why you bought Flex Radio) and this amp was worth every penny I paid for it, oh and did I mention it has the power supply internal, runs off 120vac and draws about 9-10 amps full power according to my ****-A-Watt device its plugged into, and its small about 6" tall, 13" wide and 9 or so inches deep but does weigh 26 pounds so you need a stout rack or place to put it.

Never misses a QSO either cause its fully ready to go in less than 20 seconds from turn on.


  • WimWim Member ✭✭
    edited March 2018
    yep, I use the same and very happy with this setup, I need to configure settings for the band output via USB to make the amp follow the Flex bands but that's it, great combo !
  • WayneWayne Member ✭✭
    edited June 2018
    I dont have the auto tuner so it auto senses the xmt band and adjusts itself without any issues.
  • Roger,  W6VZVRoger, W6VZV Member ✭✭
    edited May 2019
    How many watts out do you get with the KPA500?  Is it over 500 or is that the ceiling?
  • WayneWayne Member ✭✭
    edited June 2018
    With 35 watts in I get 560 out consistantly if I raise the input power to 40 watts I get 640 watts. consistantly. The 640 watts shows in the yellow zone of the power leds but creates no faults or issues if your swr is good. I generally run between 32 and 35 watts which outputs between 512 and 560 watts.

    The Kpa500 is a tank and was originally tested at over 600 watts during the testing phases prior to release for sale. It will also accept as little as 3 watts input which drives the output to about 50 watts.
  • W8QBW8QB Member
    edited June 2
    Wayne, do you use an external tuner?  Based on your own day to day experience, how high of SWR does the Kpa500 withstand before faulting to protect the finals?  You likened this amplifier to a "tank", but how well protected are the finals from occasional human error, e.g., accidentally/momentarily driving the amplifier while inadvertently using the wrong (non-resonant) antenna?  Thank you.
  • WayneWayne Member ✭✭
    edited December 2018
    I have an mfj 962d tuner inline and an isolator just after the kpa500 which I use when needed on 40 and 80 meters to get my swr to about 1.3:1. The kpa will run with up to 2:1 swr but likes 1.5:1 better. I have by accident applied 90watts drive to it 3 times within 40 seconds which caused a hard fault each time instantly when keyed which I had to reset with a power cycle each time before I realized what I was doing wrong and it never affected it.

    I have only tripped it once on high swr fault and it has an attenuator it switches in prior to faulting onhigh reflected power
    The kpa500 manual is available online. I purchased my kpa used it was made in 2016 and have had it a little over a year.
  • W8QBW8QB Member
    edited April 2019
    Thank you Wayne!
  • Amlan - AI6XNAmlan - AI6XN Member
    edited July 2018
    If you accidentally overdrive it,it trips. Happened with me a few times, but like Wayne said it’s built like a tank. Nothing happens to it. One of the happiest users of this amp.
  • PatrickPatrick WH6HI Member ✭✭✭
    edited January 2019
    You can break the solid state t/r if you do not go to bypass and don't key the amp at 100 watts drive from the radio. It happened to me. Normal drive levels are ok when not in bypass and not keying the amp. You can get away with it a few times but it will break the solidstate t/r switch. Kills the RX side in operate mode.

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