Source for 20/20 and 20/40 mfd 150V capacitors?

-- Dave M

Dave, many thanks for posting this.

Harry C.

Hi. Thats micro (not milli) Farads, right ?

Anyway, I have some 22uF/400V and 33uF/400V, 105C, long lofe (new) caps.

See :

under the "Electronic-Surplus" menu.

Regards Jan-Erik.

Harry C>

No, mfd is the traditional acronym for millifarads. The dual section

20/20 and 20/40 mfd. capacitors were a standard component of most ac/dc radios produced from WWII though (roughly) the 1960s. Dual section, tubular electrolytics in these values and rated for at least 150 WVDC are now difficult to find. (They're easily functionally replicated using contemporary products, but it's not the same thing.)

I'm quite sure that there is a cache of these NOS components lurking somewhere in a warehouse (just as old 1949 Erector Sets and Lionel Trains in unopened boxes turn up from time to time). The game, no the challenge, is in being the first one to find and unearth them.

Such motivation is a collector thing, difficult to comprehend for non-collectors.

Harry C.

dual section

of most

1960s. Dual

for at least

functionally

same thing.)

components lurking

and Lionel

game, no the

them.

comprehend for

Harry, In 50 years in electronics from WWII aircraft to Pentium and beyond I have never seen mfd used as Milli but always as Microfarad and anyway a 20millifarad 150 volt capacitor would be tooo big to fit on your workbench I think.

--
John G

Wot's Your Real Problem?

"Harry C> No, mfd is the traditional acronym for millifarads.

No, "mfd" is the tradtional aconym for MICROfarads.

Note that this dates from the days before we learned how to use the Greek lower-case "mu" symbol (?). Sometimes seen as uF (with conventional lower-case U masquerading as the "mu" character for those without the full character- set.)

TODAY, of couse, "m" means MILLI (as in mW, mV, etc.) But in the vintage of those old fire-bottle capacitors, mfd (or MFD) was definitely *MICRO*FARADS.

And to complete the history lesson, mmF (micro-micro- Farads) was used before "pico" came into common use.

8 mmF is what today we would call 8 pF (picoFarads)

A 20 milli-farad high-voltage capacitor would approach the size of the whole equipment.

John, you caught me in a big goof. Obviously mfd refers to microfarads. I was trying to make a distrinction between mfd and mmf (now termed pF).

Hey, it's only an error of three orders of magnitude! :-)

Thanks for calling attention to it.

Harry C.

And the "u" is *MUCH* better then the "m" for "micro", IMHO...

Jan-Erik.

Why do you believe this, since the Greek letter 'mu' is symbolized in our alphabet by the letter 'm', hence what you see sort of looking like a 'u' with a decending leading edge, is really an 'm'. Let's cut to the basics:

Note that the SI symbology for 'micro' is represented by the Greek letter "mu", represented in our alphabet as 'm'. See:

More than any other book that I could lay my hands on, "The ARRL Handbook" over the years avoided the symbology issue almost entirely, by simply labeling mfd value capacitors with a decimal value, say

0.01, and mmf value capacitors with an integer value such as 56. This works for me. In the older issues (I checked the 1961 issue), sometimes you'd see an occasional 'mf' or the Greek character 'mu', but not a 'u' or a 'p' designation in the entire book. The same pattern held true in the 1990 issue.

In my copy of Horowitz and Hill's "The Art of Electronics" (my copy is the 4th printing dated 1998), the same pattern is followed as in the ARRL publications, with one notable exception. The double Greek letter symbology for 'micro-micro farad' has been replaced by pf. If you ask me, this is not a significant or particularly productive change, except for easing the job of typesetters! :-) Harry C.

p.s., Management organizations and Europeans both delight in promoting unnecessary changes to existing systems that already work rather well, if for no other reason than to simply call attention to something -- What that something is I'm still trying to determine! :-)

"Harry C> Why do you believe this, since the Greek letter 'mu' is symbolized in

And there lies the problem. "m" is also used for "milli" as in mW (milli-Watts), mV (milli-Volts), mA (milli-Amps), mm (milli-metres), etc. etc. ad nauseum.

"u" (the cheap-n-dirty Anglicized stand-in for "mu") is far preferable for "micro" IMHO. No opportunity for confusion with the same letter indicating the next higher multiplier.

=========================

I wondered whatever happend to mickey-mike. (g)

Jack

It went the way of the "Wouff Hong", with its notorious brown stains! :-)

Harry C.

It had an operation, and changed its name to "Pickle Fart" ;-)

--
We now return you to our normally scheduled programming.

Michael A. Terrell
Central Florida