[T3] My Brain looks fine...

[Keith Park]

Interesting!

Ive had a few bad mica caps, rare though even for the early ones.
The silver plated mica's of the 50's do go bad though thru silver migration.

Keith


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-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Jim Adney
Sent: Saturday, October 24, 2020 12:39 PM
To: type3 at vwtype3.org
Subject: Re: [T3] My Brain looks fine...

On 23 Oct 2020 at 20:53, Keith Park wrote:

> I dont think you'd get 6 or 7 uF in a package that size at that voltage in
> a film cap, they'd have to be electrolytic or tantalum, did they have
> Tanty caps back then?

Yes, these seem to be on the small side for film caps, but maybe too large 
for Al electrolytics. I turned to Google.  

WIMA groups their caps into 3 or 4 letter families. Their web site isn't
much 
help, as this cap is part of the MKBS family, now obsolete. Google, however,

found a discussion of what these were, including an ebay auction for our 
EXACT cap, here:

https://is.gd/6NdiTn

It's a metallized polycarbonate film cap, not a film/foil cap which would
have 
been bigger. For some reason, polycarbonate film is no longer made, but it 
appears to have been a great, high reliability, choice at that time. There's
a 
discussion of it here:

https://is.gd/ty3Ai7

I have some Ta caps from the late 60s, but I don't know how common they 
were then. Probably mostly military, and expensive.  

As far as your old caps comment goes, you deal with caps that are a LOT 
older than the ones I deal with. Your antique radios were made in the
infancy 
days of electronics, and I suspect that reliability of parts made in those
days 
was quite varied.  In general, I've found Al electrolytics to age poorly,
but 
most others are usually fine. OTOH, the old HP400 AC voltmeters all have 4 
film caps that are ALL bad by the time they are 30 years old, and I even had

a bad mica cap in one of them. They all failed by becoming leaky. That was 
the only bad mica cap I've ever heard of.

BTW, those old HP400s are excellent, once the 4 leaky caps are replaced.

-- 
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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