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8-digit counter in a Madison? Why?

Discussion in 'CB Radio Modifications' started by nomadradio, Jul 28, 2018.

  1. nomadradio

    nomadradio Analog Retentive

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    So, why would you need an 8-digit counter display on a President Madison CB base?



    Simple answer is you don't. 6 digits are plenty. But this customer wanted it, so here's what we found getting it installed.

    There are a few differences between this one, the SanJian PLJ8-LED display and the 6-digit PLJ6-LED we normally use. Biggest difference besides the extra two digits is the voltage regulator. The 6-digit version has an analog regulator. This one uses a switchmode-type.

    This increases the digital noise this thing generates, and we had some issues with "zing" noises in the receiver audio.

    We mounted this one on a sheet of plexiglass to keep the counter board's ground isolated from the radio's chassis.

    [​IMG]

    This 1980 Madison radio's original clock was the mechanical type, and leaves a nice big hole on the metal chassis under the bezel. I tried mounting it on the front face of the metal panel, but parts of the plastic faceplate bezel interfered with it. Mounting it on the inside of the panel improved the clearance, but causes the digits to be set back from the window in the bezel more than I like. Some days you just have to compromise.

    Fixing the digital-noise problem proved not too tricky. A 0.1uf disc cap from the counter ground to chassis ground, and a 330uH filter in the positive power lead took care of that. Had to extend the length of the negative power wire and hook it to the big filter's ground on the radio's pc board. The positive side is tapped off the power switch.

    [​IMG]

    I neglected to shoot a pic of the input hookup. It's the same as we use for the 6-digit version. A .001uf disc connects the input-coax shield to the pcb ground alongside the VCO test point. A 470-ohm 1/4W resistor is inserted between the radio's VCO test point and the center lead of the input coax.

    I should have put the top cover on the radio before shooting this one. The smoked plex hides the ugly stuff pretty well that way. But stray room light makes all of it visible here.

    [​IMG]

    There are some other oddball differences in how this counter operates. If you want all eight digits, you have to use a 1-second gate time. This means the display won't update until a full second after you turn the clarifier. Not a user-friendly feature. The PLJ8 display allows you to use a prescaler, or to set the gate time to 1/10th of a second. Or both. The 6-digit display updates roughly ten times per second, IIRC. The setup options on the 8-digit version allow this, and it's the best option as I see it. You only get 7 digits, but so what?

    Your mileage may vary.

    Most radios won't have a window wide enough for 8 digits anyway, but this one did.

    Just goes to show that just because you can doesn't always mean you should.

    73
     
    #1 nomadradio, Jul 28, 2018
    Last edited: Jul 28, 2018
    Dmans and Klondike Mike like this.

  2. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    I have a President Madison just like that. Now you got me thinking....
     
  3. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    I also have a Madison of that vintage. However, the original clock functions 100%, and I won't be removing it anytime soon. :D

    ~Cheers~
     
    Tallman likes this.
  4. loosecannon

    loosecannon Sr. Member

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    very cool!

    yes, i agree that there really is no need for this, but hey, if the counter fits, install it!

    nomad,

    I know this install is already done, but it looks like your are starting to do more of these.

    On the analog clock Madisons, if you look at the back of the faceplate where the clock window is, you will see that a piece of 1/8" plexi will fit right in there and sit flush so it won't interfere with anything.
    you can put a piece of smoke plexi in there.

    that way, you can mount the counter board on plexi like you did, but you can cut a rectangular hole in the middle so that the digits can get a bit closer to the faceplate.

    you could actually use black plexi or other plastic for this, or you could paint the surrounding plastic with flat black paint.

    this would look very clean as the digits would be dimmed and the rest of the window would look blacked out.

    That big window sure seems like it opens up a bunch of possibilities doesn't it!

    IMG_20140528_210344.jpg


    I like the idea of using caps to ground it in order to keep it DC isolated from the chassis!

    again, very cool.
    thanks for the ideas.
    LC
     
    Dmans and Shadetree Mechanic like this.
  5. Dmans

    Dmans Well-Known Member

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    Nomad,
    Very Cool!
    Any plans/ideas to add some"clever" switch, light, push button, kitchen sink, rocket launcher, turbo engage…….. to the now unused "clock set" holes in the face?

    73's
    David
     
  6. nomadradio

    nomadradio Analog Retentive

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    Nope, left it to the radio's owner to plug the holes with whatever he can find at the hardware store.

    73
     
    Dmans likes this.
  7. kaos513

    kaos513 Well-Known Member

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    I had did similar work to a 142 gtl i had back in the days, worked great and sold it didnt last 1 week on fleabay lol
     

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