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Dentron Clipperton L Distorted Audio

Discussion in 'Amateur Radio Amplifiers' started by K5RWD, Jan 21, 2020.

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  1. K5RWD

    K5RWD Ham Member QRZ Page

    I am hoping someone can steer me in the right direction. I purchased a Clipperton L amplifer a while back and it has worked well, however now I'm getting distorted transmit audio on both SSB and AM modes and on all bands. I have another amplifer (SB-200) next to it that does not have this problem in the same connection chain, so I'm doubting it's an RF issue (per se). I hooked up a dummy load and it's still distorted (but not quite as bad). I have tried grounding and ungrounding the unit but no change.

    The amplifier has a harbach replacement board and new caps. I can not get in touch with the original owner, but I verified that some upgrade work was performed on this unit. Hopefully not by a CB'er. : (

    The amp puts out the rated power with no issues other than distorted audio. I found a place here in San Antonio that repairs amplifiers (http://www.hamrepair.com/), however shipping to them would be quite expensive (Yes, they require you to ship it although I'm local).

    Thanks for any ideas you may have,

    K5RWD
     
  2. W1VT

    W1VT Ham Member QRZ Page

    Is it one of the earlier ones without a tuned input? Or the later ones that has a tuned input. Bill Orr's Radio Handbook has a good explanation of why you may want a tuned input in a grounded grid amplifier.

    Zak W1VT
     
  3. K5RWD

    K5RWD Ham Member QRZ Page

    Yeah, I believe it's the older one without the tuned input. I had another one a long time ago and I got by using an external tuner which worked fine. I don't think the tuned input issue is the problem here. : /
     
  4. W1QJ

    W1QJ Ham Member QRZ Page

    The distortion comes from hum in the filament transformer because the filament does not have a center tap. There are ways to fox it. Google should find the fixes on the web.
     
    W2VW and K5RWD like this.
  5. K5RWD

    K5RWD Ham Member QRZ Page

    I did come across some articles on this. I will look into it more. Thanks.
     
  6. KE0ZU

    KE0ZU Ham Member QRZ Page

    Here is what you need do to fix the hum problem.

    The added transformer is a 6.3V, 1Amp unit, with the primary winding simply insulated and tied off.

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    When you get to the "linked" pics, Click the partial text at the bottom of the pic.
     
    K5RWD likes this.
  7. KE0ZU

    KE0ZU Ham Member QRZ Page

    The hum problem should have been there all along and probably quite noticeable by others. As to the sudden distortion, my first question would be, what (have you) changed? suddenly load different? Too much plate current? What?

    Might check the Zener/Bias voltage, maybe it died.

    Too much drive will cause flat topping really wide signal and lots of splatter, or perhaps you've developed a bad tube.

    A bad tube would be simply found by pulling one of them, tuning up at about 60% of your "normal" output, and checking to see if the distortion is still there. If so, swap out the next tube. And so on until you've swapped out all of them, or you found the bad one.
     
    K5RWD likes this.
  8. W1QJ

    W1QJ Ham Member QRZ Page

    The lack of a filament CT will cause hum but probably not major distortion. Bad distortion is probably a very very poor B+ regulation indicating a bad filter cap(s) breaking down. That should be checked as well. A shorted zener wouldn’t necessarily cause distortion but the zener is easily check with a meter or checking to see if idle current is significantly elevated.
     
    K5RWD likes this.
  9. KJ7MX

    KJ7MX Ham Member QRZ Page

    K5RWD likes this.
  10. K5RWD

    K5RWD Ham Member QRZ Page

    Hello, thanks for your input. Yes I did come across this article. I ordered the transformer and give this a try. I may also try the remove tube at a time and check as well.
     

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