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MFD - does this mean millifarads or microfarads?

Discussion in 'Electronic Basics' started by Wesley Hunt, Oct 11, 2004.

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  1. Wesley Hunt

    Wesley Hunt Guest

    I need to replace some capacitors from the the crossover networks in a
    couple of speakers. They are rated in "MFD". Does that mean millifarads,
    or microfarads? Also, is the "50 VMP" that follows the capactitance
    rating sigificant? Thanks in advance for any help.
  2. Jamie

    Jamie Guest

  3. colin

    colin Guest

    probably millifarads, as m = milli or mega and its hardly likly to be mega,
    microfards is usualy u.

    Colin =^.^=
  4. Before the metric system of units was in widespread use in the U.S.
    mfd was the standard way to represent microfarad. Pico farads were
    labeled mmf (micro micro farads). I doubt there any millifarad caps
    in any cross over filter.

    I have not seen the unit VMP but I suspect it is a form of voltage
    rating. (voltage momentary peak, perhaps). You could replace it with
    a 50 or more volt rated film capacitor (very large) or a nonpolarized
    electrolytic (not as good or as long lasting but small and cheap).

    This place sells lots of crossover parts:
  6. colin

    colin Guest

    I agree this maybe so after all, i just looked through my BIG box of
    capacitors >330uf some very old and they are all labeled with uF exept for
    one wich is 220MF and its hardly big enough to be 0.22 F so it must be

    If it was a huge subwoofer crosover might it just be 1 milifarad ?

    This just adds to the confusion in circuit schematics, and spice simualtors,
    the number of times ive ended up with lots of 1 milliohm resistors in a
    circuit wich required 1Mega ohms !!!

    Colin =^.^=
  7. Wesley Hunt

    Wesley Hunt Guest

    I need to replace some capacitors from the the crossover networks in a
    The speakers are from the late 60's (KLH Model Twenty), and the cap is
    about 2cm across and 5cm long. It is rated at "2 * 4 MFD", with 3 leads-
    2 red, and a common black lead.
  8. Al

    Al Guest

    I remember that once we called them "Mickey Mikes."

  9. (snip)

    I am pretty sure that I have seen both designations on both parts and
    schematics over the last 50 years.

    But you are probably right that MMFD was more common than MMF (which
    would have been confused with magneto-motive force).
  10. Gary Lecomte

    Gary Lecomte Guest

    Back in the 50's & 60's, it was Very Common in Tube Schematics to see
    MFD Representing Microfarads.
    Actually it took me a long time to get used to uF.

    Just like the change from Cycles to Hertz.
  11. Dave VanHorn

    Dave VanHorn Guest

    Old: MFD New: uF Microfarads, F/1000000
    Old: MMFD New: pF PicoFarads, F/1000000000000 (tiny!)

    The british use nanofarads, as in 1000pF = 1nF

    Anything like you described, is going to be in microfarads, and the present
    day replacements will be a lot smaller.
  12. ---------------------
    MFD is microFarad.
    milli would be a HELL of a low pass knee!!!
    Like maybe between 0.1 & 1.0 Hz??

  13. colin

    colin Guest

    yes rather low, a 1 millifarad in series with an 8 ohms speaker would give
    20hz rollof point... a sub sub woofer.

    Colin =^.^=
  14. John, you missed it. You should've associated VMP with your following
    sentence. It's not VMP, it's VNP, volts non-polarized - the usual
    marking on electrolytic caps used in crossovers.

    Putting a 'millifarad' capacitor in a speaker crossover would almost
    guarantee that the tweeters would be damaged.
  15. Apparently you have two tweeters? The common black lead should be from
    the speaker terminals, and the two red leads should each go to one of
    the tweeters. You should replace this cap with two capacitors, each
    rated 4 microfarads, 50 Volts non-polarized.
  16. (snip)

    Excellent. I knew where I wanted to go, but not how to get there.
  17. Wesley Hunt

    Wesley Hunt Guest

    The speakers are from the late 60's (KLH Model Twenty), and the cap is
    No, both red leads go to the same tweeter. I guess they were cheaper
    than 8 uF caps.
  18. BobGardner

    BobGardner Guest

    Also, is the "50 VMP" that follows the capactitance
    You bet. I think its VNP 'volts non polarized'... its isnt electrolytic... and
    its got to handle the peak to peak voltage from the amp... 200V would be better
    for a big amp (+-100V)
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