Yes, the flat molded micas are starting to show their age. Although
generally more reliable than paper, I have found some bad ones in recent
1940s TV projects.

When in doubt, check 'em!

I read somewhere else that the plastic casing in Black Beauties, etc.,
developed microscopic cracks and admitted water vapor over the years,
causing the same problems as in paper caps.

Phil Nelson

"Phil Nelson" wrote in message
...
Yes, the flat molded micas are starting to show their age.
Although generally more reliable than paper, I have found
some bad ones in recent 1940s TV projects.

When in doubt, check 'em!

I read somewhere else that the plastic casing in Black
Beauties, etc., developed microscopic cracks and admitted
water vapor over the years, causing the same problems as
in paper caps.

Phil Nelson
That may be, they certainly develop very large cracks
sometimes. I've disected a few BBs. The capacitor itself was
distorted, oddly flattened rather than being tubular.
Perhaps they were wound this way or perhaps some sort of
differential shrinkage of the encapsulation pushed them out
of shape. They were _supposed_ to be very long life, low
leakage, deluxe capacitors and are generally found in high
quality equipment.


--
---
Richard Knoppow
Los Angeles, CA, USA

I think the designers were using the best materials & technology available
at the time. And they never imagined that people might be using or restoring
these devices several decades beyond their expected service life. Most
radios were considered appliances. Contemporary electronics, even cars for
that matter, are not designed to remain in use forever. I remember when my
Dad bought a Mercury in 1965, his one and only new car. What would the
salesman have said if Dad had asked how that car might be running some
40-odd years later? Dad is still alive, bless his heart, but the car
perished decades ago.

:-)

Phil Nelson

"Richard Knoppow" wrote in message
...
That may be, they certainly develop very large cracks sometimes. I've
disected a few BBs. The capacitor itself was distorted, oddly flattened
rather than being tubular. Perhaps they were wound this way or perhaps
some sort of differential shrinkage of the encapsulation pushed them out
of shape. They were _supposed_ to be very long life, low leakage, deluxe
capacitors and are generally found in high quality equipment.

"Phil Nelson" wrote in message
...
I think the designers were using the best materials &
technology available at the time. And they never imagined
that people might be using or restoring these devices
several decades beyond their expected service life. Most
radios were considered appliances. Contemporary
electronics, even cars for that matter, are not designed to
remain in use forever. I remember when my Dad bought a
Mercury in 1965, his one and only new car. What would the
salesman have said if Dad had asked how that car might be
running some 40-odd years later? Dad is still alive, bless
his heart, but the car perished decades ago.

:-)

Phil Nelson

My memory is that the problems with the BBs began
showing up pretty soon after manufacture. For instance,
Hammarlund used them in SP-600 receivers made in the mid
1950's but the military was replacing them in mass with disc
ceramics by the late 1950's, so something must have changed
pretty rapidly. However, they were still being advertised in
the early 1960's so, perhaps, the problem was cured and it
was only the early versions that were bad.


--
---
Richard Knoppow
Los Angeles, CA, USA

Phil Nelson wrote:
I think the designers were using the best materials & technology
available at the time. And they never imagined that people might be
using or restoring these devices several decades beyond their expected
service life. Most radios were considered appliances. Contemporary
electronics, even cars for that matter, are not designed to remain in
use forever. I remember when my Dad bought a Mercury in 1965, his one
and only new car. What would the salesman have said if Dad had asked how
that car might be running some 40-odd years later? Dad is still alive,
bless his heart, but the car perished decades ago.

My Mom still drives a '68 Rambler, and my Dad drove a '65 Dodge Dart
up until he died a couple of years ago. The car is still on the road.

-Chuck