Driving An Amplifier

Discussion in 'Amateur Radio Amplifiers' started by N9CUC, Nov 5, 2016.

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  1. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I see you're less than an hour from Bloomington. I'd start by asking these folks who's in the area that could take a look at your installation and help you troubleshoot this problem: http://www.bloomingtonradio.org/

  2. N9CUC

    N9CUC Ham Member QRZ Page

    FYI here,
    I called Ameritron and told them what was going on. They are stumped too.

    Not sure where to go or what to do next.

  3. KI6LZ

    KI6LZ Ham Member QRZ Page

    Start over. Take all your equipment/cables over to your friends house and try to recreate problem.
  4. N9CUC

    N9CUC Ham Member QRZ Page

    Could the fact that neither my transceiver (Yaesu FT-950) or the 811H amp are grounded be causing the problems?

    Again, the problem is I cannot get the 450ma plate current or 100ma grid current in the initial tune up steps.
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Grounding should not make any difference.

    Based on your most recent posts it seems you cannot get ANY plate current over the 75mA bias level on ANY bands. Have these symptoms changed?

    If the question is why you don't get exactly 450 mA plate current, that can depend a lot on the exact load you're tuning into which is one reason several of us have recommended testing into a dummy load. If you don't get ANY current rise above bias levels when attempting to transmit through the amp then something is very wrong.
  6. W9RLG

    W9RLG Ham Member QRZ Page

    Please correct me if I'm wrong. didn't you state that you had taken the amp over to the Ham Station and he was successful in tuning the am the way it should tune?? Riddle me this then If the am was working properly at the Ham Station, something is wrong with your station not the amp. Maybe i'm confused, but it seems reasonable to start looking at your station not the amp. just my 2 cents worth


  7. N9CUC

    N9CUC Ham Member QRZ Page

    Yes Bob, I agree. But........what could it be?????
  8. W9RLG

    W9RLG Ham Member QRZ Page

    Could be cable ends. almost anything. I would start from the very begining, taking everything apart and check each conection, even the outside antenna connection. It could also be where the connector is attached to the antenna, what kind of antenna are you trying to use?? It will be something simple probably and you will smack your head once you find it!!


    K7TRF likes this.
  9. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Good advice above. When faced with an intermittent problem like you've seen (sometimes works, sometimes doesn't), start from scratch and take it one piece at a time. Try to find ways to replicate the problem or at least test each subsystem component thoroughly to make sure it really does work correctly.

    For instance, start with just the rig, a coax jumper cable, power/SWR meter, and ideally a dummy load or at least a well matched antenna and an empty band so you're not interfering with anyone. See if you get full output, wiggle connectors, try to replicated drive problems out of the rig, perhaps try different coax jumpers and again stress the connections and settings to see if you can replicate any problems.

    Assuming that all works then add the amp in line and repeat the process.

    If the rig, coax jumpers and connections are all good and you cannot replicate any issues with power out into a known load but you still can't get any drive into the amp using the same interconnection cables then there's some issue with the amp, likely on the input side.

    There's no real shortcuts or easy fixes to troubleshooting intermittent problems, but try to use structured approaches like testing one component at a time. The fact that it seemed to work properly down at Ham Station isn't really relevant now if it currently is not working. Troubleshoot the problem in front of you one step at a time and once you figure out what's not working correctly you'll probably understand why it worked before but does not work now.

    Good luck and reach out to local hams or ham clubs for help if you're not comfortable with this kind of step by step troubleshooting.

    Here's an example of things I'd want to test if I were troubleshooting a similar problem:

    - Am I sure the rig puts out appropriate power into a known load without the amp connected?
    - Am I sure the coax jumpers I'm using consistently make good connections and do not have intermittent faults?
    - When I add the amp in line am I sure the rig still supplies appropriate drive power to the amp and isn't folding back its output? (think about putting a power/SWR meter in bypass mode between the rig and amp to validate drive power into the amp)
    - Is it a question of no drive into the amp at all (no power out of the amp and plate current not rising above bias level) or just less output power than expected?

    There's more you can test as in rig and or amp settings to make sure everything is set up properly but take it one step at a time and test everything thoroughly including wiggling cables and connectors while operating to make sure you don't have one or more flaky cables causing you headaches.

    Good luck,
  10. N9CUC

    N9CUC Ham Member QRZ Page

    Thanks for all the ideas folks. Keep the ideas coming.

    I went through all the steps in the manual again a little while ago. Everything works until I get to the point where I am supposed to increase the drive to 450ma plate current or 100ma grid current. I can only get up to 300ma plate and 35ma grid. This is the problem, has been from day one except when it would work on 40M a couple of weeks ago.

    Next step is to replace/switch around the jumper cables. Not sure where I go next after that. I am still getting the High SWR reading on the AT on the FT-950 when I transmit, however.


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