Mirage B3060 Brown face burnt circuit

Discussion in 'Amateur Radio Amplifiers' started by N8ZI, Aug 20, 2019.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The schematic shows the 2 pF cap right across the antenna connector, like the small molded coil L2 which you show in your photo.

    I'd use a 2 pF, 500V NPO ceramic cap.

    To tune the amp to have the same output across the whole band, you do need to do that with a dummy load and adjust both the input trimmer and the output tuning trimmer, experimentally (while the amp is transmitting at full power, so you need a good, insulated alignment tool for this and can't use a metal screwdriver) to peak output first at 144, then peak at 148, and then set both about midway between those two peak settings, etc.

    I have a B3016 and it achieves ~150W output with 25-30W drive across the entire band...into a dummy load. Into my 2m vertical omni, which is tuned for 146 MHz, it doesn't -- it favors the high end of the band where the antenna is almost perfectly matched, and the low end of the band falls off in power.
     
  2. N8ZI

    N8ZI XML Subscriber QRZ Page

    Different angle photo showing where it is soldered to the board.
    Ok WB2WIK caught the blown cap first as I was off in 2 cycle fumes outer space.
    Yes I meant to say inductor but I typed capacitor for some odd reason. Also WB2WIK schematic shows where the one I downloaded on my phone doesn't.
    Now that I know what went up in smoke, any ideas on the proper V/W 2pf capacitor and a good source?
     
  3. N8ZI

    N8ZI XML Subscriber QRZ Page

    Thanks Steve.
    I will have to look close at your schematic to figure out where the input/output trimmers are after my mixed gas buzz wears off.
    I bought a set of the plastic tools before, when i tuned the slugs on my SB200, so I do have experience in that area. Also having several relatively accurate SWR/power meters and dummy loads I should have no problem moving the amplifiers sweet spot where it needs to be.
    Thanks again for the assistance :)
     
  4. N8ZI

    N8ZI XML Subscriber QRZ Page


    Don, thank you for the much needed assistance :)
     
  5. WB3BEL

    WB3BEL Ham Member QRZ Page

    On the 3016 I have here which is an older brown face, the 2pf cap is down at the other end of the coaxial cable near the 750pf. Sorry the pictures are not clearer.

    2pfCapacitor.jpg

    The part at the connector end is just bare wire.

    BussWire.jpg
     
  6. N8ZI

    N8ZI XML Subscriber QRZ Page

    Harry, thank you very much for the guidance :) You went the extra mile to pull the cover off your amplifier and compare innards :)
     
  7. N8ZI

    N8ZI XML Subscriber QRZ Page

    Interesting they are both brown face amps yet very different on the internal layout.
     
  8. N8ZI

    N8ZI XML Subscriber QRZ Page

    Just a quick search shows a
    2.0 pF 500v NPO 5% Ceramic Dogbone capacitor is $1.25 plus shipping from Surplus Sales.
    Atleast the $54 x 2 finals are not smoked :)
     
  9. WB3BEL

    WB3BEL Ham Member QRZ Page

    Where does the 2pF cap go on your unit, and how do you know you need a new one ?
     
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    It is vaporized. The picture shows it missing near the coax connector.
     

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