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Flex-5000 not getting 100w out on most bands

N8FNR Member ✭✭

I have been off the air for a while but now need to sell my Flex-5000 to help pay for my 6400 that is on order. Today out of curiosity I hooked it up to my LP-100 watt meter and a Heathkit Cantenna dummy load and am getting wildly varying outputs and can't figure out why. Below are the readings I got today. The internal ATU is turned off by the way. Did a data base reset just to make sure that that is not the issue. Running the latest version of KE9NS PSDR There is one coax run to the LP-l00 coupler and another to the dummy load. The power supply is a Astron RS-35M.

         LP-100           PSDR

160 1.24:1 83W   1.2:1 89W

80 1.27:1 83W     1.0:1 89W

60 1.28 :1 79W     1.4:1 87W

40 1.29:1 81W      1.4:1 92W

30 1.28:1 81W      1.1:1 88W

20 1.27:1 76W     1.6:1 89W

17 1.26:1 73W      1.3:1 81W

15 1.26:1 74W      2.0:1 91W

12 1.23:1 72W      1.3:1 80W

10 1.22 :1 85W     2.1:1 100W

6 1.26:1 50W        2.5:1 82W

Does anyone have any thoughts as to why I am not getting close to 100W out on most bands? Also how can the output on 6M be explained that the LP-100 is showing?


Zack Schindler



  • WX7Y
    WX7Y Member ✭✭✭
    edited June 2020
    First off I would really wonder about the Heath-kit dummy load,  If it's been in Oil all these years it could have changed values. Mine only lasted about 10 years before I had to replace the Resister with a MFJ resister because it deteriorated enough so it was no longer 50 Ohms and if I remember right there was carbon in the bottom of the can. 

    Your voltage output from the Power Supply should be at least 13.8 Volts preferable to be a little higher but not over 14.2V. 

    Also try a different Coax jumper IF the resister reads 48 to 52 Ohms on a known good DVM. 

    not sure if this helps at all.


  • John
    John Member
    edited June 2018
    I wonder if this is down to the two final devices not being matched. I don't know if this was done at production or not or even after a repair job, but probably is one of the reasons why we don't get 100w on the dot.

    John -M0ELS
  • FRED  W9TB
    FRED W9TB Member ✭✭
    edited January 2019
    Zack , I have had 3 different 5000a over the years and all were about the same  as yours. Any where from 110 watts to 75 watts depending on the band. The best one I have had is one I traded for and it is over 10 years old and I love it. Just hope I like the 6600M that I have on order as well.

  • Jon_KF2E
    Jon_KF2E Member ✭✭
    edited July 2018
    As Bret said you need to have 13.8VDC at the radio. Just as a reference 13.8VDC from a power supply will only yield 13.01 through 10 feet of 12 AWG wire. Lots of hams don't cut their power cables and as a result add unwanted voltage loss to their radio. If you can, measure the voltage at the radio while in transmit and I think you will see most of your problem.

  • N8FNR
    N8FNR Member ✭✭
    edited June 2020
    I put a Wattsup meter between the Astron and the rig and see 13.61V unkeyed and 12.53V/12.16A keyed at full drive on 6M. Would that account for the lower output on 6?
  • Bill -VA3WTB
    Bill -VA3WTB Member ✭✭✭
    edited February 2018
    At least 13.8 on key up is best, If you don't have full voltage on key up, can effect it. Your power out readings are not that far out anyways.
  • N8FNR
    N8FNR Member ✭✭
    edited June 2020
    I wonder if my power supply is failing. Walked back into my shack and there is that bad electrical smell. Unplugged the PS from the wall and noted the the heat sink on the back of the Astron is hot. Perhaps it is time to buy a new one.......

  • Chris DL5NAM
    Chris DL5NAM Member ✭✭✭
    edited April 2020
    Always use a PSU at a level of 60 - 70% max. If your TRX need 20 -22 A DC  at max power out then your PSU should rated 35 A.

    Next problem is; many Ham's using wrong wire for connection between PSU and TRX. Mostly to thin and mostly to long. With 13,8V and 22A every mm² and inch length counts.

    And not forget: give your TRX AND PSU also a good ground connection !
  • Unknown
    Unknown Inactive Employee
    edited September 2019

    To be able to draw 22 amps, you will need #10 gauge wire to keep the voltage up at that current.  And if you are using PowerPoles, maybe sure the pins are pushed in and best to use the 40 amp connectors, not the 20 amp connectors.   In PowerSDR  use the internal "Information"  window to give you the voltage and temperature of the internals of the radio ,  best and easiest way to know if you are getting enough voltage to the radio ..   Anything under 13.0 volts UNDER FULL LOAD ,  will be a decrease in RF output.  With all working correctly normally about .6 of a volt drop from RX to full output TX is normal...   If the supply itself is not dropping voltage, but you are at the radio ,  start looking for wiring or connection issues..   by the way,  the older Astron analog regulated power supplies are known for loosing regulation over time due to the regulator chip and pass transistors..   So just because it's an old power transformer regulated power supply ,  does not mean it's good forever and it's good to periodically check your connections at the rear of the power supply, many have issues starting right at the back of the supply ..  

    I think that I still have an old Cantenna dummy load some where too, but there are some good commercial dummy loads available on Ebay at a reasonable price too..  


  • WX7Y
    WX7Y Member ✭✭✭
    edited June 2020
    The astron PS are very good power supplys but the 2n3055 will die and if one dies the they will still produce power out but current ability will be way down.  I think the Astron 35 uses 3 2N3055's one to drive the other two.
    There is a **** on the regulator board inside that you can increase the voltage output, adjust it to 14.2V. 
    Loosing 1.5 Volts drop with 22 AMPs current tells me
    1: to small wire
    2: Wire length is to long for the wire size , Increase size of wire between radio and power Supply or cut out excess.
    3: using Anderson / PowerPole connectors or something like a RIG Runner you NEED to use 45 Amp connectors and NOT anything smaller they just don't handle the current. 
    4: power supply 2N3055 Regulator transistors are BAD.
    5: BIG Electrolytic capacitor that the regulator board is **** on to is leaky.

    Time for a new Power supply depends if you can check those things and repair it your self if the power supply does have issues.

    Hope you didn't have the radio connected to it when you smelled the smoke. 


  • JDE
    JDE Member
    edited January 2018
    After a certain time with the Astrons, the 2N3055 was replaced with the 2N3771 for higher wattage and current handling.

  • KE9NS
    KE9NS Darrin Kohn Member ✭✭
    edited January 2020

    I did discover setup->PA settings->  CTRL + ALT + A

    If you believe the built in watt meter appears to be calibrated correctly, you can calibrate the PA using a 50ohm dummy on ANT1

    I didn't research the source code, but it doesn't appear to write the calibration results to the EEPROM, but it probably writes it to your database file?

    Maybe Tim can elaborate on this.... If its fairly safe to use this "Calibration" for the PA?

  • Unknown
    Unknown Inactive Employee
    edited January 2018

    The menu was for the SDR-1000,  not for the 1500/3000/5000  , where the SDR 1000 did not have any EEPROM to store calibrations and will not modify the PA settings in the EEPROM.   With out the proper external  equipment to perform the calibrations you can easily over drive the PA or make the IMD horrible .   Best left to the automatic process to perform the calibrations.   In my years of supporting the 5000, the majority of times (maybe 90%)  slightly low outputs on all bands was due to wiring errors or power supplies not regulating correctly ..   The radio were calibrated with 13.8 into the radio at full current (18 to 22 amps)   any lower and the power drops off ,  get to 12 volts and you might lose 25 % power ,  but still would not be much of a difference at the other end..  

    Best thing to do , is to make a chart of the power output per band measuring the output in PSDR , external meter, current being drawn and voltage using the   Crtl - shift -i   ,  for internal voltage..   You could have a situation that one band , maybe 20 meters is low RF output but is drawing the same current ,  maybe a bad PA filter..   These are the things that charting will help with troubleshooting.   

  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited January 2018
    Your power output is reasonable except for 12m.  If the recommendations for ensuring that the radio has the full 13.8 VDC at the radio does not provide any relief, then I recommend that you open a HelpDesk support ticket so that you can send in the radio and have it recalibrated.
  • Mike  W1BFA in Maine
    Mike W1BFA in Maine Member ✭✭
    edited June 2020
    My 5000 was always a little soft in the power department but after checking with the meter I saw that most of the problem was in the power cable itself.  In re arranging the station I located the 5000 closer to the PS and shortened the power cable by a little over 4 feet.  It really perked things up.  This was with an Astron 35.   Funny thing, I am using the 6500 on the same power supply with the factory cable (about 6') and that produces full power easily.   Mike  W1BFA

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