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Boomer 400 RF making 50 amp switching power supply buzz.

Discussion in 'General CB Services Discussion' started by 2315 Robert, Feb 13, 2018.

  1. 2315 Robert

    2315 Robert Active Member

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    Have a boomer 400 that was causing my 50amp switching power supply to make a slight buzzing during modulation into a dummy load. I took two ferrite clamping beads and installed them on the power wires and they buzz like crazy. What would cause this? I noticed that the internal variable cap. in the Boomer has no effect on anything. Nothing touching like solder or flux on the traces. There is swr is 1.7 after the Boomer and the reflect is about 20-30w on a MFJ 826B. I know that these are low quality but, something is going on here.


     

  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Most switching supplies have a slight buzzing sound when heavily loaded. Speaking of that how much power output are you running?. It could be that the power supply is under-rated and being taxed hard to supply enough current to the amp.
     
    Tallman likes this.
  3. 2315 Robert

    2315 Robert Active Member

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    400. I have one of those amp/voltage/watt demand meters that I can run in line and it reports that I am drawing 220w and 17.87amps max. It is a Mega Watt supply that only runs the Boomer. Output wise keys at 110w and swings to 410W(Probably not realistic that is what the meter I have shows). The other thing I find interesting is that on key it is super stable on the meter as far as frequency in the MFJ as well as a thief on coax frequency counter. Thank you for your reply.
     
  4. nomadradio

    nomadradio Analog Retentive

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    Sounds more to me as if RF from the Boomer is getting into the power supply, and disrupting the regulation circuits.

    A .01uf disc cap each from the power supply's pos and neg terminals to the chassis is a good start. Clamp-on ferrites on the DC output as close to the terminals as you can get them might help.

    73
     
  5. 543_Dallas

    543_Dallas Sr. Member

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    Most of the cb amps don't have sufficient filtering on the power leads. The positive power lead connects to the collectors of the transistors right next to the output transformers.

    Some .1uf bypass caps from b+ to ground and wrapping the power leads through a large ferrite core several times can help. The split beads you clamp on can rattle, I've heard some that made good talk back. A lot of the amp builders use stacks of ferrite on only the positive lead. Most of the time that works.
     
  6. 2315 Robert

    2315 Robert Active Member

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    Will give that a try. Thank you. I actually bought the 50 amp to run the Boomer. I have a 36a that did not do this. Also my inline showed around 30 amps draw.
     
  7. 2315 Robert

    2315 Robert Active Member

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    Still looking for ferrite that I could use in this way. DXE is were I have purchased large 31 3/4 id ferrites from is pricey. I know that the right blend/number of ferrite is important. Even on amazon they are up there. For the price some companies are looking to get the ferrites they should do the dishes. Thank you for the reply.
     
    ShadeTreeMechanic likes this.
  8. 543_Dallas

    543_Dallas Sr. Member

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    Amazon is too expensive for this kind of stuff most of the time. I bought some of these cores from mouser electronics and they may be what you need. Look carefully at the dimensions and datasheet. These may not be what you need but they sell a variety. The wrong mix of ferrite can be useless.

    https://www.mouser.com/ProductDetail/623-5943003801

    Don't forget about the bypass caps. They are dirt cheap and may be all you need.
     
  9. Big Kahuna

    Big Kahuna Well-Known Member

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    Does the buzzing get more intense when you modulate on AM? That's definitely a sign the RF is making it's way into the power supply. When you get into really big amps if there's enough getting in you can hear your voice plain as day. Not ideal. :) Although now that I think about it that really was more common with the older power supplies and not the switching ones. I've been using the MegaWatt for years without any RF issues on them even when testing some dirty CB amps.
     
  10. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    It could also be a process called magnatostriction. When a laminated transformer buzzes it is because of eddy currents in the core. If you think it is RF getting into the power supply put a couple of .01 uf capacitors on the output.. One directly across positive to negative, one negative to chassis ground, and one from positive to chassis ground. That should eliminate the buzz and leave the ferrites on the wires.
     
    #10 Tallman, Feb 13, 2018
    Last edited: Feb 13, 2018
    ShadeTreeMechanic likes this.
  11. 2315 Robert

    2315 Robert Active Member

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    Thank you for the link.
     
  12. 2315 Robert

    2315 Robert Active Member

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    Only when modulating on AM(SSB no problem and as fine as an auto SSB can be). BK this Boomer was out of control. Had 4 same lot 455's(used all of Nomads advice to tame this shrew) pulled them and installed 1446's(much better low gain transistor). If I remember correctly this was not the case with my 36AMegaWatt(with the 455's it was pulling 34 amps). That supply can get ran next to scope with minimal interference. I really like MegaWatt so I want to make sure that I am not coming across saying anything negative against the power supply. Thank you for the reply.
     
  13. 2315 Robert

    2315 Robert Active Member

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    Copy that Tallman. Will do. Will update tomorrow. Thank you for the reply.
     
  14. 2315 Robert

    2315 Robert Active Member

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    Tried the caps: chassis to ground, ground to positive, and positive to chassis and no change. Emailed MegaWatt a video said that it was the sound of the large transistor in the power supply. He advised that it is not hurting anything. Thanks to everyone for your help.
     
    Tallman likes this.
  15. 2315 Robert

    2315 Robert Active Member

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    Tried the caps: chassis to ground, ground to positive, and positive to chassis and no change. Emailed MegaWatt a video and JM said that it was the sound of the large transistor in the power supply. He advised that it is not hurting anything. Thanks to everyone for your help.
     
    Tallman likes this.

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