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Power level down buy 10-20 watts

George M.
George M. Member ✭✭

 My Flex 6600’s output power has been slowly dropping over the past few months. So, I decided to investigate. Using a calibrated HP 436 power meter and sensor (H/p8482A) and a characterized high power 30db pad. The Flex shows 80-90 watts on HF and ~75 watts on 6m. The watt meter in SmartSDR shows about the same thing. DC going into it on key down is 13.6v and is drawing ~22amps. All have read above 90 watts in the past.

  Also, on an LP-500 station monitor it shows about the same and this is into a load with a 1:1.12 +/- 0.2 SWR across all bands.

  Could something inside the Flex have changed value, been stressed? Everything in my antenna system checks out according to several VNA analyzers I have, with no apparent intermittency’s.

  I have been running long transmit duty cycle modes like RTTY and digital but not at full power. (5-50w max)

 I've also made sure the inside of the 6600 is clean and the fan is running, and max output settings are set to 100.

Flex Info,

SN 1120-1088-6600-4670

HW v3.4.23.15544

No Options

Hate to send this in for repair, would be without radio for the duration and with field day and other contests coming up…☹


George M. N1NAZ


  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi George, try bumping your power supply up to 14.2 V. I did that and now get full output from my 6400.

    Another thing to check is the fuse inside the radio. It is a bit sneaky to get to, but some have reported that pulling and reseating the fuse restores full power. The problem that solves is corrosion on the fuse contacts.

  • George M.
    George M. Member ✭✭

    Thanks Ken Will try that now and open the rig up tomorrow and reset the fuse. Where is it on your 6400?

  • KD0RC
    KD0RC Member, Super Elmer Moderator
    edited May 19

    Hi George, You remove the top cover (can't get to it from the bottom), then remove the tuner and the filter board. Under there somewhere is the fuse. It is a bit of a pain to get to, but very doable. I think it is in the same place on the 6400 and 6600 models. From the hardware manual:

    7.1.1 Fused Internally at 30 Amps

    The power input has a protective 30 Amp automotive “blade type” fuse inside the radio case. In the event you ever need to replace the internal fuse, remove the top cover and locate the fuse in the rear corner of the PA board just inside the case adjacent to the Anderson Powerpole connector.

    The manual doesn't mention removing any boards, but that is what I had to do.

    EDIT: Forgot to mention... The case takes a T5 or T6 Torx bit (sorry, can't remember which).

  • George M.
    George M. Member ✭✭

    Well, here is what I Found, the 30-amp fuse was a bit corroded so cleaned and reseated, moved supply voltage up to 14.2v to cover the losses. SDR monitor program now shows 13.6v on key down and around 110deg F. I have external 25-amp fuses just before the power poles (pos and neg) going into the 6600, the negative side was blown. Haven’t figured out why yet, replaced. So other ground paths were being used to complete the neg path. Always wondered if the neg side should really be fused, you can find all kinds of theories for and against that one.

    Anyway, the power level is higher, 85+ watts, but not where it used to be. Still checking.

    Yes, I know, that much difference in power output will not make any difference, so let’s see it stays stable at these levels and does not drop any further.

    Len KD0RC, T9 Torx bit, and thanks for the sugestions.

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Thanks for the detailed feedback George, that will help others with similar issues.

    Sounds like you still have some voltage drop between power supply and radio. I would bump the supply up closer to 15 V so that the measured internal voltage is closer to 14 V.

  • George KF2T
    George KF2T Member ✭✭✭

    Hi George,

    Same symptoms here, too. Did you find anything further that helped?



  • George M.
    George M. Member ✭✭

    Hi George,

    After I completed the above, all but 6 meters came back to spec. 6 is still low (about 85-90). nothing else seemed to help. DC input to the 6600 is 14.3V dont want or need to go any higher. Not going to make that much diff in making contacts.

    I will post more if I find anything.

    George N1NAZ

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