[Milsurplus] replacement question -

[Bill Carns]

Another perspective......Quality Control lax.....I think not.

These caps are pushing 70 years old.....There are failure mechanisms related
to metal migration, inter-metallics and dendrite growth that were totally
unknown at that time of the development of communication technology and
component manufacture.

We did not learn about silver migration and inter-metallics really until the
6os..  

To infer that there must have been some kind of manufacturing process QC
breakdown is way going the wrong direction.

The design life cycle for those radios was measured in months,  They were
subjected to gunfire, chemical invasion, vibration beyond imagination - Ever
ridden in a radial engine aircraft when the 20s were in operation - and
temperature and altitude cycles that would kill any current consumer
product.  Those radio were damn well made...it is amazing how well they have
lasted.

Go gather yourself up a couple of pictures off the internet of the
production lines at the time, the trucks used to haul parts and the building
they were built in....Then remember that the resulting radios were used
often in battle, then surplused out and then bought by us, stored under
often deplorable conditions and then brought back into operation.

QC problems.....I think not....What you are looking at is a wonder of
manufacturing given the time and state of the art.

Just enjoy what is left of the original stuff that still does work as
designed 80 years later.

Bill
N7OTQ

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Richard Brunner
Sent: Saturday, August 10, 2013 3:16 PM
To: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] replacement question -

I once resurrected an RBL receiver, and a dozen mica capacitors and only one
oil-paper capacitor failed. I just checked the instruction book, and it says
"Capacitor, Molded Mica."  Some are suspiciously large for mica,
1000 to 8000 mmfd, so they could have been paper.  Maybe quality control was
lax during WWII, but I have been suspicious of micas ever since.

Richard, AA1P

>> capacitor replacement .
>>
>> "Normally" the Silver Micas never need replacement but if they have 
>> to be replaced could that be effectively replaced with a modern ceramic
with the appropriate tolerance and temperature characteristics.  which leads
me to this question:  In WW2 what were the typical characteristics of a
Silver Mica capacitor?
>>
>> Just shoot me for asking.
>> Hutch
>>

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