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How to measure rf chokes?

Discussion in 'Amplifiers' started by dozerman, Jun 2, 2018.

  1. dozerman

    dozerman hello, its me again

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    I'm sure there is another thread or ten on here about this, but I've not been able to figure it out. With minimal equipment, how does a person measure chokes in a Maco 200. The choke on the tag strip feeding the driver and the one on the tank coil underneath are the two I'm talking about. The schematics I've looked at just have them labeled as L something or other, with no values.


     
    ShadeTreeMechanic likes this.

  2. Robb

    Robb Yup

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    An MFJ antenna analyzer has that function.
    Or you could get a dedicated handheld capacitance and choke tester.
    Either one
     
  3. loosecannon

    loosecannon Sr. Member

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    that's because you can change the way a coil acts by deforming it, but still have minimal effect on the actual microhenry value of the choke.

    for example, we all know how much spreading coils in the harmonic filters after the final section in a CB radio can wreak havoc with the transmitted signal, but if you were to measure one of those coils, spread it, and then measure it again you would find that the value of the choke hasn't changed much, but its ability to do its job has been greatly diminished.

    I guess what i'm saying is that there is more to a coil's function than just its uH value.

    I have found tutorials online for making your own air wound coils. i will see if i can find the one i used when making coils for my tube amp build.
    LC
     
    ShadeTreeMechanic likes this.
  4. dozerman

    dozerman hello, its me again

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    With them being pretty diminished, getting black, will the chokes still measure their values or doesn't that change as they get burnt?
     
  5. dozerman

    dozerman hello, its me again

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    I understand what you're saying about the coils. Oven thought about winding a couple but I know I would get the value off, and that of course will have an effect on things down stream. I'm trying to revive one that was bought DOA. New everything but the board with the pre amp. Always hated those, they seem to fail easily. I replace them with a keying circuit from @nomadradio. Works great. And who needs a pre amp to pull in more white noise.
     
  6. OldTech03

    OldTech03 Active Member

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    Low level white noise can help you sleep? LOL
     
  7. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    The best way to check a coil is with an Impedance bridge. There are other test you can do if you have the equipment. If a coil is charred windings could be shorting out changing the inductance. If it is a transformer Isolation of primary and secondary could be compromised and the would smoke transistors.
     
  8. dozerman

    dozerman hello, its me again

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    Well I do like some kind of noise when I sleep, like a fan. But static from a pre amp, no I can't stand
     
  9. dozerman

    dozerman hello, its me again

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    Yeah from what I read online that's what the consensus is. Just hate to buy something else to measure these chokes. Wish the schematics showed their values. Would make life's much easier
     
  10. nomadradio

    nomadradio Analog Retentive

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    A value if 22 uH is typical for the small choke on the input side. Varmint used 56 uH.

    Any value in between is probably close enough.

    The plate choke is probably about the same 22 uH value, but it's built to take more current. Ohmite used to make a part called "Z28". It's pretty much a universal plate choke for up to 2 or 3 tubes. They made a larger one called "Z14" that should be good for up to 4 tubes.

    Found a Z14 on Fleabay, https://www.ebay.com/itm/Ohmite-Z-1...105807?hash=item43eb19320f:g:akUAAOSwxp9W4wJS

    But a search for "Z28" will get you pages and pages of the wrong item.

    73
     
  11. Dmans

    Dmans Member

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    I ordered a couple Z144's and a Z28 (from Newark I believe) a couple years ago for my Afterburner repair after first getting it ("Working with Great Output!"). It seems it took a while to get it, but if you have the time.............and I do.
    73's
    David
     

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