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Unregulated Power Supply Building

Discussion in 'Home Brew' started by Nitmare67, Feb 19, 2009.

  1. dudmuck

    dudmuck Active Member

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    Unregulated supply is safe for class C amplifier.



    Although Its unsafe with a linear amp with unregulated bias, because the amp would be over-biased during low RF drive.

    However, for AM, the power supply sagging on audio peaks is the opposite of what you want.

    The ultimate setup for AM would be to modulate the control input of the LM723 with your audio, instead of the RF signal feeding the amplifier. Capacitors on the collector of the finals would need to be reduced to accommodate the audio frequency. This would assume the LM723 has the bandwidth for audio. Such a configuration would only need a deadkey RF input, but would be louder than anything.
     

  2. unit_399

    unit_399 EL CAPO

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    Dudmuck -

    Power supply "voltage sagging" is only a problem if the transformer can't supply adequate current under peak load. The unreg supply I built has two microwave transformers that I removed the HV secondary and rewound using #8 teflon insulated wire that I got at Home Depot. With my TX600 amp connected, the supply idles at 15vdc, and drops to 13.8 when dead-keyed. If I whistle into the mike (100% modulation) the voltage drops to 13.6, which is NO problem.

    The secret to unreg supplies is to design it to give you what you need.

    - 399
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Agreed. Unfortunatly pretty much ALL purchased unregulated power supplies have had NO design thought whatsoever put into them. I will agree with you now that I know what you did regarding your supply but I wonder how many others just take an off the shelf xmfr and load the shit out of it and see a voltage drop of 5-8 volts or so. I can see that YOU did the right thing and my statement above regarding my feelings about unreg. supplies is a generality directed at those units simply purchased off the shelf even if purchased from someone who "designs" them in his basement shop. ;)

    BTW tnx for the PM. It's all good. (y)
     
  4. cyclops1970

    cyclops1970 Gay Nazi Liberation Party

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    How long have you been around here? Not to toot QRN's horn, but anyone doing this:

    http://www.worldwidedx.com/home-brew-mods/31848-rca-broadcast-transmit-80m.html

    Has got my vote for having electrical cajones.
     
  5. mechanic

    mechanic Well-Known Member

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    Where's the popcorn!? :LOL:


    mechanic
     
  6. Nitmare67

    Nitmare67 Member

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    What is the proper amount size capacitor to use per amp?

    Or what voltage ripple is acceptable?
     
  7. linearone

    linearone King of NY

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    8000uf per amp
     
  8. Nitmare67

    Nitmare67 Member

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    Wow i had heard 1000 uf per amp before. What percent voltage ripple does this yield?

    Is this what normal over the counter fatboy, worldwide unregulated power supply use also or is this a much better method?

    I could basically use a 1 farad cap then. Too bad audio caps are normally only 20V!
     
  9. linearone

    linearone King of NY

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    someone asked this exact same question on another forum a few weeks ago. here is my reply to them

    The filter capacitor size can be approximated from C=IT/E where I is the current, T is the half cycle time (8.33 mS at 60 Hertz), and E is the fall in voltage that will occur during one half cycle.

    in all practicality i use 100,000uf or so to smooth a 100 amp supply.
    never had a problem with using more, just be sure to use a soft start of some sort.
     
  10. spider451

    spider451 Member

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    linearone great answer and as far as fatoy 2 piece base amps supply goes i seen a 10 pill 2x8 using 5800 uf for 280 amp supply it eventually allowed ac hum across the lines and fizzled out. it was sad that a friend paid so much for this device through a reputable shop that sells lots of these and has had to have fixed this trouble before and they did nothing before sale to warn customer or stop the problem before hand. so in conclusion fatoy does not have the caps in them they need for long term use. i know im going to get flamed for this statement but i've got my fireproof suit on so flame on. most repair techs on this forum know i'm telling the truth unless something has changed that i'm not aware of.
     
  11. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Gee and to think my regulated 40 amp Tripp-Lite PR-40a came with 64,000 uF of filtering. I later upgraded it to 110,000 uF using a single large cap I acquired.
     
  12. Cajun Invader

    Cajun Invader Membership Moderator

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    Why would you get flamed for saying that? This isn't a FatBoy sponsored website.

    You will however get flamed for calling a 2x8 a 10 pill.:love:
     
  13. W9WD

    W9WD Guest

    32 electronic power supply projects

    I bought this book
    32 electronic power supply projects
    back in the 80s (I think) and have built a few of the power supplies out of it and they work!

    Gives some good basic theory and explains components and what they do

    Amazon.com: Used and New: 32 electronic power supply projects
     

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