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IRF520A

Discussion in 'Home Brew' started by Crusher, Mar 2, 2008.

  1. Crusher

    Crusher Well-Known Member

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    Hmmmm.... the splitter and combiner look almost identical to what are in the TS units. Those cores have a very low permeability (u)

    Crusher.


     

  2. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    Pictures of Crusher`s work on the MOFSET project

    73
    Jeff
     

    Attached Files:

  3. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    Another Mofset picture.

    73
    Jeff
     

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  4. GRTS

    GRTS Galaxy Tech

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    The plastic mounting screws on the mosfets will be a problem.
     
  5. DIRTYWHITEBOY

    DIRTYWHITEBOY Active Member

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    Looks like the mosfets are biased when the amp is in recieve or turned off,whats up with that?
     
  6. mackmobile43

    mackmobile43 Jock Supporter

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    maybe they're teflon and yes dwb I too think it's seeing bias voltage whenever the power is attached.
     
  7. Crusher

    Crusher Well-Known Member

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    I used the plastic screws, because the holes are to small for standard insulators. I need to install a relay/switch so that yes the bias will be turned off when in standby. First mosfet amp I ever built, so yeah I have a few items to address yet.
     
  8. Crusher

    Crusher Well-Known Member

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    The #4-40 screw insulators is what i was referring to. They are too big for hole in Mosfet. As these need to be electrically isolated from heatsink.
     
  9. Crusher

    Crusher Well-Known Member

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    Last night, I installed a relay so that when keying circuit is activated, it turns on relay and supplies voltage to biasing circuit. That way there is only voltage applied when circuit is transmitting. Anymore ideas or suggestions are welcome.

    Crusher
     
  10. mackmobile43

    mackmobile43 Jock Supporter

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    (y)(y)
     
  11. Crusher

    Crusher Well-Known Member

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    Thanks 43, never really thought of installing it, did not seem like a problem at time but as i said, it was something i overlooked. That amp likes about a 2 watt DK and works nicely. Put about 12 hours on it now and seems to work fine. But I know what GRTS meant about nylon screws, as they heat up, plastic tends to expand and eventually pressure is taken off of transistor and can't dissipate heat nearly as well and poof. Magic smoke. LOL
     
  12. Crusher

    Crusher Well-Known Member

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    Someone had told me at one point that IRF550A mosfets would make for a nice small amp. Boy were they wrong as so was I for not looking at datasheet. Just in case anyone else was thinking about trying something slightly bigger in the same family so to speak.
     
  13. mackmobile43

    mackmobile43 Jock Supporter

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    The issue with the screws can be solved by drilling the holes of the transistor tabs lager and using the teflon shoulder washers or by placing a flat metal strap across the transistors with a single screw through it to the heat sink.
     
  14. 4600turbo

    4600turbo Active Member

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    Why use MosFets. When you could put in 4x2879's and get quite a few more watts out of it.





    Owner of the World biggest Galaxy radio.
    4X2879's 550-600watts. PEP.
     
  15. Crusher

    Crusher Well-Known Member

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    LOL, if I want a big box I will build a big box for myself. But I have more fun just building and experimenting with the stuff. Trying new stuff out.
     
    #30 Crusher, Mar 18, 2008
    Last edited: Mar 18, 2008

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