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Flex 6500 TX output power


I am relatively new to Flex. I have owned a 6500 for only a few months. (and loving it)
I seem to remember that it showed 100w TX output power originally, but now it never goes above 75-80 max. The RF power slider goes up to 100.
I tried it with a dummy load in ANT2 port and got much the same, so I don't think it is the antennas or poor swr causing the power drop. The SWR is generally quite low, about 1.1-1.2

I found a similar discussion on here, and downloaded the Flex Meter v1.1 software and it shows PA Temp of about 56c on TX after 10 seconds, and then drops back to around 38 after 10 minutes. I'm now guessing that it could be reducing output power based on temperature? Or maybe the output device has overheated at some point and now running below expected performance?
Any ideas or suggestions welcome.



  • Larry _ NY8T
    Larry _ NY8T Member ✭✭✭
    edited November 2021

    I would be looking at your DC voltage, make sure its stable (13.8) on idle and transmit at the radio also check the DC power pole connector at the back of the radio, itcan get oxidation on it and cause the voltage that the radio sees drop.

  • VE7ATJ_Don
    VE7ATJ_Don Member ✭✭✭

    hmmmm... 56C seems a bit high for the finals, and it could be that your fan is kicking into high speed to try to reduce that a bit. I think there's also heat-protection circuitry in the 6500 which will reduce output power to keep the temperature down.

    The FlexMeter software also includes a monitor for the the DC Voltage to the finals. As Larry mentioned, it might be good to turn this on as well and see what's happening.

    It might also be worthwhile to submit a Help Desk ticket to get one of the Flex staff to run some diagnostics with you to get the bottom of the problem.

  • M0MDS
    M0MDS Member ✭✭
    edited November 2021
    The Flexmeter seems to want to tell me the RAD ->+13.8B voltage is 3.2v offload and 2.76v on TX, which can't be right. I'm guessing it sees 13.2v offload, and reports is wrongly. I have made up a new large diameter power cable and will try that this evening when I get to the shack.

    The shack can get quite warm, especially with my old valve linear warming it up, so the PA temp is often around 30c on standby.

    Thanks for the assistance, will report back.
  • M0MDS
    M0MDS Member ✭✭
    So I tried a new power cable, and it didn't help, so I'm going to submit a helpdesk ticket. Will report back once resolved.
  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    You may want to open it up and see if there is any corrosion on the blade fuse.

    Also, do you have a calibrated wattmeter?

    Mike va3mw

  • M0MDS
    M0MDS Member ✭✭
    edited November 2021

    I can check the blade fuse again, but it looked ok.

    I did open it down last night, clean the fans and check for any obvious signs.

    Yes I do have a reasonably accurate wattmeter, which currently shows similar output, about 80w.

    Mike M0MDS

  • WX7Y
    WX7Y Member ✭✭✭

    What is the Power supply voltage at the back of the radio while transmitter is activated? Should be 14.2V to get full output from the radio, Years ago at least on the 6300, 6500, and 6700 there was a lot of Emails on here that stated that Flex used a higher voltage on the Calibration bench.

    The Anderson Power Pole connectors do have a large amount of loss, I put some silver infused heat sink compound on my connectors which seemed to help a tiny bit but mainly as a anti-oxidant on the contacts (DON'T OVER DO IT on the stuff a little goes a very long way).

    If your building a new power cable Make sure you use hi quality 45Amp contacts which are thicker metal with more spring tension.

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    Since those readings are so strange, maybe try another approach. K9DUR provides a software meter (free download). Also FRSTACK has one. They both display the voltage reported by the flex internally.

  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator

    Another question, are you measuring in SSB or by using the tune slider and tune button? The power meter in SmartSDR is not a very good peak reading meter.

    Dave wo2x

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