[R-390] Old Brown Beauty Crack Problem

[Michael Murphy]

Dallas, if you are insinuating that we are changing out those capacitors
just for fun, I don't agree. I think we do it because we have been
indoctrinated and we have to... It just feels good. We are in fact- Brown
Beauty Crack addicts.
Clearly we also need to be archiving our cut out components in the proper
environment which slows down the aging process; if only for the historical
record. I've found that Mason jars work.

Mike Murphy WB2UID

----- Original Message ----- 
From: "Dallas Lankford" <dallas at bayou.com>
To: <r-390 at mailman.qth.net>
Sent: Wednesday, January 12, 2005 9:20 AM
Subject: [R-390] Old Brown Beauty Statistics Lesson


> Disclaimer:
>
> "If you all are talking about those rained-on, snowed-on, sun-baked,
frozen,
> left in the parking lot for years, or otherwise abused R-390A's, then my
> remarks about capacitors do not apply to them.  I would not touch one of
> those with a 10 foot pole.  There are people who believe they can be
> rebuilt.  I don't.  I wouldn't buy any R-390A nowadays that I couldn't
> personally inspect before I bought it, or that didn't come with a return
> guarantee that it hasn't been abused."
>
>
> The fact that your R-390A was an (old) Motorola [see below] does not
change
> the fact that your claims violate the laws of statistics.
>
> Among the R-390A's that I have carefully inspected and rebuilt were two
1956
> Motorolas.  Let's see...  how many brown beauties were in those two.  I am
> not sure.  There were about 12 each in the IF decks, and at least 1 each
in
> the RF deck.  That is a total of 26.  If on the average we would expect
out
> of 10 to be cracked (your claim), what is the probability that none were
> cracked (my observation)?  The answer is simple statistics.  Multiply 3/10
> by itself 26 times.  That is 2.5419 time 10 to the -14 power.  So the odds
> that I would observe none when you observed 70% cracked are 1 in
> 254,190,000,000,000.  This violates the laws of statistics.
>
> The above does not include a 3rd Motorola IF deck that I still own, in
which
> none of the brown beauties were cracked or bad.  If I included it, the
odds
> would be even more outrageous, namely 1 in 1.3509 times 10 to the minus
20.
>
> BTW, both of those Motorolas are alive and well (about 20 years after I
> rebuilt them), with none of the brown beauties replaced (and none have
> cracked or gone bad in the meantime).  The only problem which has
developed
> in either is a switch which will not turn off in one of them.  The owner,
> who lives nerby, is too lazy to bring it by for me to fix.
>
> Dr. Dallas Lankford
> retired Professor of Mathematics and Statistics
> Louisiana Tech University
>
>
>
>
> ----- Original Message -----
> From: <N4BUQ at aol.com>
> To: <r-390 at mailman.qth.net>
> Sent: Wednesday, January 12, 2005 7:29 AM
> Subject: Re: [R-390] Re: Caps and more caps
>
>
> <cut>
> > A large percentage of the "brown beauties" in my '56 Motorola had cracks
> that could easily be seen.  I don't think mine was abused, but just old.
> >
> > Barry(III) - N4BUQ
>
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