On Jul 31, 2006, at 6:46 AM, mike kendall wrote:
> Rich,
> I wish my buddy's Ameritron and my own first Ameritron had caps
> that were working until we were 6ft under. In my buddy's case, the
> caps failed 4 times before the factory got it working again before
> failing quickly.
chortle. El Cheapo caps with lots of ESR, operating at the ragged
edge with normal mains V can probably be expected to buried with the
operator, or even before. Also, operating electrolytics even slightly
above the rated WV is probably not a good idea. Another problem is
excessive mains potential. Example -- I've seen 257vac here on some
mornings on So Cal Edison's own recording VM.
Editorial === As I see it, Hams would be quite likely to pay
slightly more for an HF amplifier that did not use the cheapest parts
available on this planet.
cheers, Mike
> 73,
> Mike
>
>
> R L Measures <r@somis.org> wrote:
>
> On Jul 31, 2006, at 2:41 AM, Tom W8JI wrote:
>
> >> Also, for the price on their high end units, there really
> >> is not an excuse for them to use 2,000 hour caps vice the
> >> 5,000 hour caps that are not much more. Read my earlier
> >> email about how you can expect 3 years before the power
> >> supply is beyond it's rated life expectancy.
> >
> > We can read it, but we should be aware it isn't correct.
> >
> > I'm not sure if MFJ is buying 2000 hour MTBF caps or not,
> > but the 2000 hour number is NOT the expected mean time hours
> > before failure in operation. It appears to me that is what
> > you are doing, and that what you are doing is absolutely
> > wrong. ****Everyone needs to understand this very well.
> > Whatever the raw number, 2000 or 5000 or whatever, it is NOT
> > the expected life. That is a base number used in a MTBF
> > formula.**** In other words a "2000 hour MTBF" in the
> > component rating does not mean that is the operating MTBF.
> > That is simply very wrong. Anyone who reads component data
> > sheets or application notes would know that.
> >
> > (Those caps weren't initially speced to be 2000 hour parts,
> > but that was in the early 1980's and I'm not sure what they
> > are buying now.)
> >
> > To put it bluntly, the numbers about expected life in the
> > earlier email are meaningless. They are not even correct for
> > a 450 volt part operated at 85 degrees C (185F) internal
> > temperature because, even if raised by a power of 1 (an 85C
> > cap operated at 75C internal temperature), the life is 4000
> > hours.
>
> good point, Tom. IOW, at room temp the caps are going to be going
> strong when the operator is 6-feet under.
> >
> > ...
>
> R L MEASURES, AG6K. 805-386-3734
> r@somis.org
>
>
>
>
>
> Want to be your own boss? Learn how on Yahoo! Small Business.
R L MEASURES, AG6K. 805-386-3734
r@somis.org
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