MFD - does this mean millifarads or microfarads?

microfarads.

Wesley Hunt wrote:

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:

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

Colin =^.^=

------------------ No, mmfd or MMFD.

------------------------------- This is back when a "milliFarad" or 1000 uF would be a can 3-4" tall!

-Steve

millifarads,

mega,

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 mircofarad.

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 =^.^=

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-

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.

(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).

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

Al

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.

--------------------- MFD is microFarad. milli would be a HELL of a low pass knee!!! Like maybe between 0.1 & 1.0 Hz??

-Steve

in a

millifarads,

capactitance

be mega,

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.

networks in a

capactitance

to be

tall!

leads-

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.

(snip)

(snip)

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

yes rather low, a 1 millifarad in series with an 8 ohms speaker would give

Colin =^.^=

No, both red leads go to the same tweeter. I guess they were cheaper than 8 uF caps.

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)