MX-P50M Loss of Amplification

Discussion in 'Amateur Radio Amplifiers' started by KI7AJA, Jul 25, 2020.

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  1. KI7AJA

    KI7AJA Ham Member QRZ Page

    I just bought one of those little MX-P50M amplifiers from China to give my uBITX a little bit more of a kick and worked for 2 days. Then all of a sudden it stopped working. The little power light still comes on and I can also hear the relay inside click along with the Tx light turning on when I key the transmitter. However, my power supply indicate that there is next to no current being drawn in addition to my MFJ antenna tuner indicating there is next to no power to the antenna. After doing some searching around it sounds like the little MRF186 transistor has caused some trouble for some people. My transistor had no labeling on the package itself. Is it possible that this could be the source of the problem? If so how do I confirm that it is the problem? And if it ends up not being the problem is there anything else that could have gone wrong? I’m not entirely sure what to do. I happen to have a multimeter and can do measurements between certain sections of the circuit if anyone requests.
     
  2. KW6LA

    KW6LA Ham Member QRZ Page

    Could be a lot of things? My guess.. only a guess is the the MRF 186 has blown. I see you have a tuner, which means you feed interesting ?? Antennas with this.
    These Amps DON'T like high VSWR, say over about 1.7 to 1. < so if you ran it with a mismatch, it can burn up the Final. If the amp has no cooling fan, and driven
    to the max, its only a matter of time. In the old days, you payed attention to the heat from your HT. If it gets warm ?? time to stop transmitting. Same with this amp.
    I have a RM Italy which I monitor with my hand ( temperature ) a lot. So happens, it has a VSWR reset if you do bad things. Hope another ham can give you better
    info on what and how to fix this.... bummer !!
     
  3. JIMSMITHS

    JIMSMITHS QRZ Member

    Jun 22, 2009 - Figure 1. The loss-amplification phenomenon in lamellar media. Periodic boundary conditions are imposed in all three Cartesian directions.
    Jun 22, 2009 - Figure 1. The loss-amplification phenomenon in lamellar media. Periodic boundary conditions are imposed in all three Cartesian directions.


     
    KW6LA likes this.
  4. KW6LA

    KW6LA Ham Member QRZ Page

    Jim- Speaking as an outsider... how do you view the rest of the world ?
     
  5. KI7AJA

    KI7AJA Ham Member QRZ Page

    It didn’t ever get warm, however the antenna I was using had a 3:1 mismatch, but I thought the tuner would protect the amp from the reflected power. I could be wrong though.
     
  6. KW6LA

    KW6LA Ham Member QRZ Page

    Tuner should protect it if no arcing and in good condition. I have no experience with MRF 186, but have destroyed many MRF 455 amps in my day. Easy to fix , grease, new MOSFET and the base resistors can go with them. You might look for some burnt components? Metering part values in the amp. Start at the basics, fuse, or a diode (s) and
    go from there. Go online Google / YouTube and see if anyone has posted info on the Amp. I am supersized, RF engineers haven't jump in on this one yet? Or with an Amp
    they call ( CB type ) they wont !!!! I wish you best of luck.
     
    Last edited: Jul 31, 2020
  7. KI7AJA

    KI7AJA Ham Member QRZ Page

    Ok thanks, I’ll keep looking, so far the voltage regulator and the transistor are acting funny. I have an Elmer coming over today, so maybe he can help me fix it.
     

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