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PGXL 120V AC low output

RebelXT Member, Unconfirmed
Hey folks, I wonder what output you are getting from your PGXL (running on 120V AC) compared to what you are driving it with? Specifically, in order to get 500 watts out, what power do you feed your PGXL with?

For context, I used to drive my PGXL with 30 watts and would get 500-550 watts out on all HF bands. A few weeks ago something changed and I now get 250 watts out when driving my PGXL with 30 watts. I did the following tests using a high power dummy load to rule out any potential issues with my antennas and TGXL. For instance, with 20 watts drive, PGXL output into a dummy load is 160 watts while PGXL consumes 980 watts, indicating relatively low efficiency. Appreciate any data points from the folks running their PGXL on 120V AC.

Drive, watts PGXL output power into dummy load, watts PGXL AC power, watts

15 114 860
20 160 980
30 250 1250
40 340 1360
50 460 1500

alex KD5RBU


  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin


    Do you have MeFFA turned on or off as this will affect drive levels.

    What is MEffA?

    And when to use MEffA, Mode AB, or Mode AAB.

    MEffA stands for (Maximum Efficiency Algorithm) and this feature noticeably increases the efficiency of the amplifier when processing constant-level tones or non-AM signals, such as CW, RTTY, FM or FT8 type signals. It works by decreasing the drain Voltage on the amplifier devices, requiring more drive, which moves the amplifier closer to a higher efficiency “Class C” operation. It is only available in “AB” mode.

    It is not applicable to amplify signals with varying amplitude, such as SSB, AM, or FT8. These modulation modes require the use of Mode “AAB” which provides maximum linearity, but at a lower efficiency than Mode “AB” because you are operating closer to operating the amplifier at Class “A”.

    Important Note: Though the MEffA box may be checked in the PGXL Windows App, it is active only when the amplifier is in Mode “AB” and has no effect in Mode “AAB”. You can operate in Mode “AB” without MEffA enabled, which still offers mild improvements in amplifier efficiency, especially for constant-level signals, relative to maximum amplification linearity.

    Adjustment of MEffA at a desired power level requires a “tuning” procedure.

    Key the amplifier with a “Tune” or drive signal, to establish the desired output.

    Unkey the amplifier then re-key. (You may note that the amplifier drops the Drain Voltage and see the corresponding drop in output level). This is MEffA working.

    Increase drive to re-establish the desired output level. Then repeat the process (starting with step 2 until the desired output power is achieved for every time keyed.

    You are now ready to operate.

    If you don’t want to go through this process, you can leave MEffA off (box unchecked in the PGXL Windows application) and use a fixed drive level that should always correspond to a fixed power output for a given band.

  • RebelXT
    RebelXT Member, Unconfirmed
    Hey Mike, sorry I forgot to mention this in the post - MEffA was off during all of the tests. In fact I have always had it turned off.
  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    With MeFFa off, your efficiency will be less.

    If you are still concerned, you may want to follow up with a support ticket.

  • RebelXT
    RebelXT Member, Unconfirmed
    Sounds good Mike, I have an open ticket and someone from support team is helping me. The reason I asked the question on the forum is to see what efficiency other PGXL users (who run it on 120V) have seen.
  • K4QXX
    K4QXX Member ✭✭

    I had the same issue with my amp, although not running 120v (running 220). I used to be able to run around 50 watts to get 1500 out. All of a sudden, 50 watts was only getting me 700-800 watts out. The amp took a trip back to Flex and it's now working well again.

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