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Siltronix 90. How NOT to make it digital.

Discussion in 'CB Radio Modifications' started by nomadradio, Oct 12, 2018.

  1. nomadradio

    nomadradio Analog Retentive

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    I bought this Siltronix VFO on Ebay with the intention of converting it to the 6-digit LED display we normally use, with a new smoked-plex faceplate.

    My customers don't like LCD displays. They like LEDs, they say. My intention all along was to convert it our way.

    Just the same, it seemed worth posting a "How Not To" based on this toy.

    First clue that this conversion had problems is the displayed frequency.

    [​IMG]

    Turns out this counter display is *NOT* the one that lets you program an offset frequency, so it can display the operating frequency.

    [​IMG]

    This one is a straight frequency counter. It only knows how to display the actual frequency you feed into it.

    Oops.

    The input hookup is interesting. A simple unshielded wire stuck into the center hole of the SMA socket. We don' need no stinking plug. Or shielded wire either, apparently.

    [​IMG]

    The power hookup is wrong, too. The orange wire is tapped into the zener-regulated 7-Volts that powers the oscillator. Pretty sure there isn't enough spare current to run the display's backlight LEDs. Didn't spend any time to see if this made the drift worse, but it can't help.

    [​IMG]

    One part of the stock setup we always change is the CB/HF band-change circuit. This trimmer cap is factory-original, but it's the reason the VFO's output level falls in half (or less) when you switch from the "CB" to "HF" band.

    [​IMG]


    But that would bring us from "How Not To" to the "How we do it" post.

    Film at 11.



    73
     
    Dmans and Robb like this.

  2. Robb

    Robb Yup

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    Q: what chem do you use to clean the variable cap and the trolley system to keep it from hanging up?
     
  3. nomadradio

    nomadradio Analog Retentive

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    Biggest problem with the main tuning cap is at the ground-contact spring on the rear end of the rotor shaft. We use a length of fat cotton string, soaked in CRC-brand "QD" non-residue cleaner to remove the old lube and oxides from the surfaces where the spring touches the end of the shaft. I wrap the string halfway around the shaft and it will slip between the spring and shaft end. A little back-and-forth on the string will scrub away most of the accumulated schmoo. I add a drop of silicone oil to restore lubrication.

    Uhh, "trolley system"?

    If you mean the planetary-reduction drives, making sure that the shafts are centered on axis usually takes care of slippage problems. We find that most slippage is due to excess friction, almost always from slight misalignment.

    73
     
    Robb likes this.

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