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  1. #1
    New Member
    Join Date
    Nov 2016
    Location
    Middletown, NY
    Posts
    2

    HL-2.5Kfx reduced gain

    I suddenly have a problem with the amp.....the gain is not near what is was or should be. I never usually drive it with 100 watts, didn't need it. Now, after this failure, I can barely get 1400 watts out and when I drive it with 100w, it faults to the message for driving it with mismatched band (which isn't the case) and says gain less than 5. Does anybody have any idea where I should start looking?
    Thanks, Paul, N2PD

  2. #2
    New Member
    Join Date
    Nov 2016
    Location
    Middletown, NY
    Posts
    2
    I found the problem. There is a 3db 100w attenuator located on the bias board which is the first thing,the rf from the exciter sees. Apparently, the properties of the device had changed. Instead of 3db attenuation, it was closer to 6db. Because the exciter power is measured by the amp prior to this attenuator, it wasn't seeing the gain expected by the amp and reported this error, and obviously it required more drive for a given output. I was not able to obtain the exact replacement, but used instead one from Henry Radio with the same specs. Unfortunately, the original was a two-hole screw mount and the one I used is a one hole. After removing the damaged part, cleaning the heat sink and applying fresh thermal compound, I installed the new attenuator and now all seems well. Output for a given input is back to where it was, output is good on all bands, and no more fault message. Before I discovered the problem, I bought two new mosfets from digikey, Now they will be spares (nice to have anyway in case the ARF 1500 goes obsolete.) Incidentally, even though the attenuator was damaged, it still presented a low VSWR!! Thought I should put this up here in case anybody else has this problem.
    73 to all, N2PD

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