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Question about this clarifier Mod

Discussion in 'CB Radio Modifications' started by Toltec, Jul 29, 2017.

  1. Toltec

    Toltec New Member

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    https://www.radiomods.co.nz/grantxl8719.html

    Has anyone here ever done clarifier mod Version 2 from the above link? Looks interesting. Basically it gives you a bit of a more even slide, promises 6khz up and 6khz down. I've done it before and it definitely works and is a bit more even than the usual clarifier mods you find on the internet except in my case the slide was more like 4khz up and 7khz down or something, which is still a lot more even than what you usually get.

    On the bottom of the mod instruccions it says you can make it a bit more stable if your radio is boosted by using a 7808 regulator for the 8V source. I've tried it before with good results also, however one part of this confuses me. Step 9 asks you to connect the jumper of D51 to pin 3 of the regulator IC. This is the reference pin for the MB3756 regulator. Measuring this gives you 8V. What's the point of connecting here? Would it be the same to just also hook this up to pin 1? Same voltage and everything. I don't quite get it. If I used the 7808 regulator would is it still best for me to use that connection?


     

  2. Loyal Servant

    Loyal Servant Well-Known Member

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    I would not connect anything to Vref.
    That's certainly a mistake.
     
  3. Robb

    Robb Yup

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    That's hilarious!

    Because it is over-complicating an otherwise very simple and practical mod. Simply snip one end of D58, and then run the voltage supply wire from the clarifier directly to the 3756 voltage reg.

    Done.
    This mod will also allow for centering the clarifier as well after alignment (required).

    More slide? Also means more room for drift error. Also extends the range to go between channels - which can fall prey to FCC problems. Also means loss of centering the clarifier. Stock slide level doesn't have that issue and is quite stable. Unless you are bent in re-inventing the wheel and make more work for yourself than needed for just the clarifier.
     
    LeapFrog likes this.
  4. Toltec

    Toltec New Member

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    Alright I thought so.

    I actually like the mod. Like I said I've done it before and I've found that it gives me better slide on both halves of the clarifier than other mods I've done before. The use of the Vref pin definitely weirded me out though, I'm glad that's been cleared up. Other mods usually give me a very small amount of slide on one side, and a huge amount of slide on the other side, up to the point where the radio goes out of lock. The 7808 regulator thing kinda makes sense to me. The built in regulator doesn't seem to be as stable as a modern day linear regulator. If your radio is highly modded or you aren't on the most stable power supply an individual power supply for the clarifier can help. An extra step, probably unnecessary in most cases but it can be worth it. Overall the mod is a bit more complicated than others but not by much and defo worth it, the 8V regulator can be omitted. The slide offered isn't crazy, 6khz up and down ain't so bad, still keeps the clarifier manageable for SSB.
     
  5. Robb

    Robb Yup

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    If the OEM mb3756 has enough supply to operate w/o the clarifier mod; then it will work equally well w/o the need for a dedicated 7808 voltage supply with the mod.

    What makes your choice of clarifier mod better?
    Considering the other downsides mentioned; or did you not consider them at all?

    In fact, if you wanted to extend the clarifier range; then why go to all of the trouble of bypassing resistors ('hacking ad naseam') - when all you have to do is add a 5mh choke between the varactor ground and chassis ground? At least you can maintain a center position on the clarifier.
     
    #5 Robb, Jul 29, 2017
    Last edited: Jul 29, 2017
    LeapFrog likes this.
  6. sp5it

    sp5it Master of puppets

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    I performed similar mod, but I used LM9240-12 LDO as voltage source for varicap. Voltage is stable as long as voltage from power supply is over 13V.
    Mike
     
    tecnicoloco likes this.
  7. nomadradio

    nomadradio Analog Retentive

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    Had a local guy decades ago who modified literally hundreds of Cobra 2000GTL radios to power the clarifier from a 12-Volt zener diode. It was powered from the main 13.5 Volts.

    Tended to warble. He used custom-cut crystals in a setup like the Expo 100 kits, but with five bands total. Had s slug-tuned coil for each band crystal, embedded in a glob of black RTV silicone. The clarifier needed that extra 4 Volts to get his custom crystals to tune high enough. Just changing the clarifier to run from 8 Volts was not satisfactory. The clarifier would not reach the center of the channel properly. Didn't fancy ripping out the whole thing and installing a factory 11.3258 crystal.

    Eventually my idiot light came on, and we install a 78L12 powered directly from the power supply's unregulated side to power the clarifier control. Keeps the input side of the regulator at a high enough voltage to prevent the output from sagging. This preserves the upper range of the modified clarifier circuit. Can't use the radio mobile this way, but it's not a drawback for anyone we have worked for so far.

    Back in those days LDO regulators were not readily available.

    Using the LDO recommended above will simplify this solution.

    73
     
    tecnicoloco likes this.
  8. Robb

    Robb Yup

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    Two things to add here:

    Your stock clarifier control becomes inadequate with only 270 degrees of control space; a ten turn control pot becomes more important to have since you vastly increased the range. Otherwise. there will be too much change with little pot movement and clarifying becomes an impossible task. Or you need a 20k/1k ganged pot for a coarse/fine adjustment. Which is impossible to find - unless you have a source. Care to share that one?

    You didn't say a word about a super-varactor - which are sill available.
     
    #8 Robb, Jul 30, 2017
    Last edited: Jul 30, 2017
  9. nomadradio

    nomadradio Analog Retentive

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    Well, the Cobra 2000 has the coarse/fine dual control. Wired correctly, it's fairly smooth to operate.

    And a radio with the clarifier "stretched" on a single knob for that control will be way too touchy to use on sideband. You can probably get away with it on AM if you have a frequency display on the radio.

    I have seen two single knobs devoted to this, one for coarse, the other for fine tune. The dual controls are definitely tough to track down.

    I really don't have a lot to say about the old "super-diode" varactor. Tends to make the radio drift with temperature change. Maybe not so bad for a base radio, but not suitable for mobile use IMHO.

    73
     
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  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    I used to run a Colt Black Shadow on SSB with a stretched clarifier. It had about 800Hz down and a bit over 5 KHz up. Center slot was about eleven o'clock. This allowed me to go virtually anywhere. It was not that bad really and although it was a bit touchy near the end of it upper limit (about 7.5 KHz) it was still easy to clarify someone in at 5 KHz. Then again I hear people today saying that their stock 800Hz clarifiers are too hard to tune someone in with. I guess it depends on the operator.
     
  11. nomadradio

    nomadradio Analog Retentive

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    I remember a customer years ago who got annoyed with the "touchy" clarifier on his 142GTL. He drilled a hole in the side of the knob, and inserted a one inch-long #4 machine screw. The leverage on the head of the screw was like putting a larger knob on the control. He found it a lot easier to get a SSB station clarified this way. Put his thumb on the head of the screw and fine-tuned it that way.

    73
     
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  12. Toltec

    Toltec New Member

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    As I mentioned my main reason for not liking most of the clarifier mods that I found searching online was the uneveness of the clarifier. One side would barely make any change while the other would make a very large change. This one is roughly even on each side. I performed this again on a 148GTL this time though I did use the built in regulator and left out the 7808. Works great and is very stable. Not touchy at all.


    The simpler mod you mentioned sounds interesting, I might give it a shot sometime. However I do like the idea of having just over 6khz of slide for the sake of sneaking in the "between" areas where some of my buddies hang out.
     
    #12 Toltec, Aug 5, 2017
    Last edited: Aug 5, 2017
  13. unit_399

    unit_399 EL CAPO

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    Robb -
    The 2000GTL used a dual 1K/20K clarifier control. So did the 148GTL-Dx, SS360FM, and a lot of other early imports (especially Galaxy). I bought a bunch of them from Dynascan several years ago. Maybe they still have some in stock. I know several on-line CB parts houses carry them too. 1 kohm over 270 degrees makes fine tuning easy.

    - 399
     
  14. Robb

    Robb Yup

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    Haven't been able to find any - I've looked . . . :(
     
  15. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    I'm weird.... I remove the 11.325 crystal in my 148's/2000's/Grants and install the 11.1125 crystal. Then I remove the series range limiting capacitor. Both of these mods greatly improve stability. You might not slide as much, but +/- 5khz of slide is still possible. Drift is usually less than 50-60hz. I tie to pin 1 on the MB3756 voltage regulator and it's always worked fine.

    If I want extra channels I'll go 1/2 VDD on pin 10 of the PLL to get 192 channels.

    ~Cheers~
     

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