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Replacing the infamous TR24.

Discussion in 'CB Radio Modifications' started by El Kabong, Oct 2, 2018.

  1. El Kabong

    El Kabong New Member

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    Howdy all. I was given a Cobra 148 that is missing a few parts, such as the famous TR--24 transistor. Can anyone give me a part number for a TR-24 so I can order a replacement?


     

  2. Robb

    Robb Yup

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  3. nomadradio

    nomadradio Analog Retentive

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    You could pull out TR26 and install it at the TR24 position.

    This will leave the AM modulation open, but still allow you to set the sideband ALC trimpot VR11 below the distortion point. Without TR24, there is no limiting in SSB modes. Transmitting sideband with no limiter can be quite unhealthy for the final transistor, not to mention the ears of anyone listening on the channel.

    AM audio is more forgiving with the limiter disabled. SSB will sound like dirt without it.

    Not sure who you go to for "just one" 2SC945.

    73
     
    Shadetree Mechanic and Robb like this.
  4. El Kabong

    El Kabong New Member

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    Thanks guys. I needed that.

    One last question. Should there be two open holes near TR24? They are just forward of 24's spot and are not marked with an ID. I suspect they are unused.
     
    #4 El Kabong, Oct 2, 2018
    Last edited: Oct 2, 2018
  5. Robb

    Robb Yup

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    There are a bunch of unused holes in various places on the chassis.
    I would make sure that R131 has not been clipped or removed too.
     
  6. El Kabong

    El Kabong New Member

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    Gotcha. The two holes I am looking at are the other direction from R131. Kinda out in the open too.
     
  7. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Some of those open holes are feed through passages to conduct a signal or voltages from one side of the board to the other. Also used to jump over a traces in the design.
    Quite common on two layer circuit boards(Double Sided) Also one of the reasons you will see jumper wires going from one point to another.
     
    El Kabong and Shadetree Mechanic like this.

: Cobra 148, TR-24

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