I've seen so many warnings about these old wax coated paper capacitors
in these newsgroups, and on the web, that every time I see one of them
now, I begin to shudder.

Immediately, I notify the FBI, telling them that there is a wax coated
paper capacitor in my radio, and I know that this thing is deadly. I
carefully explain to them that I have been exposed to it, and instantly
developed capacitor cancer. I also explain that I have heard of entire
cities being reduced to rubble, killing everyone within 100 miles, when
these caps explode. Then I ask them to come remove the capacitors for my
and everyone elses safety.

Yes, I was just joking in this previous paragraph.......

Seriously, I have not been able to find any answers to what actually
happens internally to these caps, which causes them to fail. I googled
for an answer, specifically used the word PAPER CAPACITOR, but all I get
are results for failing electrolytic caps, which I do now clearly
understand what occurs with them.

So, lets say I have an old radio from the mid 1950s. It contains 9 paper
capacitors (plus a few electrolytic filter caps). I am repeatedly told
that I must replace all of these wax coated paper caps, as well as the
dried up electrolytics.

Ok, I know the electrolyte has dried up in these electrolytics and they
are no longer filtering the rectified DC voltage in the power supply,
which I can quickly identify by the 60 cycle hum coming from the
speaker.

Then, I am told I must replace all these smaller wax covered paper caps,
which may or may not be working at the moment. Great, I can take this
advice and I can change them, but it seems that no one (at least not on
the web), can seem to explain what occurs inside of their waxy bodies
that make them fail.

I know they are quite simple. I roll of paper, and two layers of tin or
aluminum foil, with leads attached to the two layers of foil inside.They
are rolled up, with their leads exiting their bodies. Then they are
given an outer shell of paper with their identity printed on it, and are
then coated with wax. I'm sure that if I had a lot of time to waste, I
could even make my own paper caps, but for the low cost they sell for,
that is not necessary, other than for an experiment.

Knowing how they are built, I can only fathom three possible reasons
that they fail.

1. The leads tend to corrode from dialectric corrosion, where they
contact the inner foil. (I have read that moisture can and does enter
these caps, even with the best wax coating).

2. Voltage arcs burn across the paper layer, arcing between the two
layers of foil, and burn a hole into the paper, which allows the two
layers of foil to contact each other, and cause a short circuit.

3. The foil itself decays from age, and loses conductivity in parts or
all of it's roll.

* This does not take into account physical damage, such as crushing or
poking a hole in a cap body.

What else can go wrong on such a simple device?

*NOTE: I mentioned the wax coated paper caps, but am aware the old
plastic coated ones such as the ones called "Bumble bees" (with colored
stripes) are just as bad.

Honestly, I find it hard to comprehend how moisture can get past that
wax, as long as the wax remains intact, but I'll just take the advice
from the experts on that note.

One final question: Does anyone know what kind of wax was used on them?
Was it bees wax, paraffin wax, or something other?

On Tue, 25 Apr 2017, wrote:

I've seen so many warnings about these old wax coated paper capacitors
in these newsgroups, and on the web, that every time I see one of them
now, I begin to shudder.

Here's a simpler way to look at it.

Paper capacitors are an old type of capacitor. ELementary Electronics
about 1971 showed how to make them yourself, some paper, some foil, some
liquid if I recall properly. I think even then I knew they were hideous,
that piece of foil was relatively large, must have inductance. We see
this, paper capacitors were often marked with "+" or "-" so you knew which
end to connect to ground. They weren't polarized, but they might pick up
unwanted signals if you connected the wrong end to ground, it was the
nature of how they were made.

They were also fairly big for the capacitance offered.

But for a time, they were what was available. When you started posting, I
got curious and apparently bypass value ceramic capacitors took some time
to become feasible, which has to explain all the old radios with paper
capacitors. When I got into the hobby in 1971, nobody would suggest paper
capacitors for bypass capacitors (and probably not anything else). "Keep
leads short", but that didn't work so well when the paper capacitor was
the equivalent of a long lead.

So it doesn't matter why paper capacitors fail, there's lots of reason to
replace them anyway because they are an antiquated form of capacitor. The
switch to ceramic bypass capacitors happened because you could get a more
reliable package, but it was also smaller, and lower inductance.

Michael

On 4/25/2017 11:05 AM, wrote:
1. The leads tend to corrode from dialectric corrosion, where they
contact the inner foil. (I have read that moisture can and does enter
these caps, even with the best wax coating).

No and yes

2. Voltage arcs burn across the paper layer, arcing between the two
layers of foil, and burn a hole into the paper, which allows the two
layers of foil to contact each other, and cause a short circuit.

Not until there is a fault.

3. The foil itself decays from age, and loses conductivity in parts or
all of it's roll.

Not so much the foil as the paper dielectric.

First and foremost, the paper was NOT acid free archival paper.
Mainly because everyone assumed the wax would seal the moisture
out. It doesn't because it is hygroscopic.
So what happens over time is moisture gets into the capacitor
paper, mixes with the acid content eats the metal foil and causes
conductive paths in the paper.
At first the leakage goes up, until some point when the capacitor
fails shorted.



--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

---
This email has been checked for viruses by AVG.
http://www.avg.com

On Tue, 25 Apr 2017 13:38:35 -0400, Michael Black wrote:

Paper capacitors are an old type of capacitor. ELementary Electronics
about 1971 showed how to make them yourself, some paper, some foil, some
liquid if I recall properly. I think even then I knew they were hideous,

I'd like to see that E.E. article. That would be sort of fun to try,
just for the heck of it.

E.E. does have PDF file reprints of all their issues on
http://www.americanradiohistory.com/...aster_Page.htm

But finding the right issue might be tough...

Guess I'll begin by downloading all the issues from 71. That will take
most of the day on dialup....

1) Cellouse is marvelously hydrgroscopic. It sucks up humidity like a
sponge. Wet cellouse is conductive. There's no reason to overthink
this. Also, don't assume the paper the manufacturers used was stored
or wound in perfectly dry conditions. That's nearly impossible. I have
no doubt caps made under humid conditions failed more quickly than
caps made during dry times.

2) Wax is NOT a perfect seal against moisture. I'm sure plastics are
better but they aren't perfect, either. Ever see a tupperware container
sweating from the inside? That moisture diffused it's way through the
polyethelyne in maybe a few days or even hours.

Paper caps from the old days that HAD to last a long time were sealed in
soldered metal cans in oil. Too expensive for consumer gear! The
engineers who designed this stuff KNEW the paper caps would be failing
in a few years. So what? Electronics changes fast and the buyer would
almost certainly buy something newer before deteriorating caps killed
the device.

Using good caps in consumer gear would be a waste of money. Cheap caps
were considered good enough.

As far as what kind of wax was used, some sources say beeswax, some say
microcrystalline wax. I don't much care.

What fails outside of paper capacitors is that anyone still gives a ****.

On 26/04/17 02:05, wrote:
I've seen so many warnings about these old wax coated paper capacitors
in these newsgroups, and on the web, that every time I see one of them
now, I begin to shudder.

Immediately, I notify the FBI, telling them that there is a wax coated
paper capacitor in my radio, and I know that this thing is deadly. I
carefully explain to them that I have been exposed to it, and instantly
developed capacitor cancer. I also explain that I have heard of entire
cities being reduced to rubble, killing everyone within 100 miles, when
these caps explode. Then I ask them to come remove the capacitors for my
and everyone elses safety.

Yes, I was just joking in this previous paragraph.......

Seriously, I have not been able to find any answers to what actually
happens internally to these caps, which causes them to fail. I googled
for an answer, specifically used the word PAPER CAPACITOR, but all I get
are results for failing electrolytic caps, which I do now clearly
understand what occurs with them.

So, lets say I have an old radio from the mid 1950s. It contains 9 paper
capacitors (plus a few electrolytic filter caps). I am repeatedly told
that I must replace all of these wax coated paper caps, as well as the
dried up electrolytics.

Ok, I know the electrolyte has dried up in these electrolytics and they
are no longer filtering the rectified DC voltage in the power supply,
which I can quickly identify by the 60 cycle hum coming from the
speaker.

Then, I am told I must replace all these smaller wax covered paper caps,
which may or may not be working at the moment. Great, I can take this
advice and I can change them, but it seems that no one (at least not on
the web), can seem to explain what occurs inside of their waxy bodies
that make them fail.

I know they are quite simple. I roll of paper, and two layers of tin or
aluminum foil, with leads attached to the two layers of foil inside.They
are rolled up, with their leads exiting their bodies. Then they are
given an outer shell of paper with their identity printed on it, and are
then coated with wax. I'm sure that if I had a lot of time to waste, I
could even make my own paper caps, but for the low cost they sell for,
that is not necessary, other than for an experiment.

Knowing how they are built, I can only fathom three possible reasons
that they fail.

1. The leads tend to corrode from dialectric corrosion, where they
contact the inner foil. (I have read that moisture can and does enter
these caps, even with the best wax coating).

2. Voltage arcs burn across the paper layer, arcing between the two
layers of foil, and burn a hole into the paper, which allows the two
layers of foil to contact each other, and cause a short circuit.

3. The foil itself decays from age, and loses conductivity in parts or
all of it's roll.

* This does not take into account physical damage, such as crushing or
poking a hole in a cap body.

What else can go wrong on such a simple device?

*NOTE: I mentioned the wax coated paper caps, but am aware the old
plastic coated ones such as the ones called "Bumble bees" (with colored
stripes) are just as bad.

Honestly, I find it hard to comprehend how moisture can get past that
wax, as long as the wax remains intact, but I'll just take the advice
from the experts on that note.

One final question: Does anyone know what kind of wax was used on them?
Was it bees wax, paraffin wax, or something other?

On Tuesday, April 25, 2017 at 10:34:46 PM UTC-4, Clifford Heath wrote:
What fails outside of paper capacitors is that anyone still gives a ****.



There is that. But, let's start with the wax: A mixture of beeswax (small amount), paraffin, and petroleum jelly for handling. Does anyone here know how old pure beeswax candles were made? Beeswax was dissolved in warm water, and the wicks were dipped multiple times into the solution, picking up a bit of additional wax each time. the keyword is *DISSOLVED*. Even paraffin wax holds water, and beeswax is directly water-soluble.

Now, the paper: Rather thin waxed paper purchased from the lowest bidder. And the wax, as above, was subject to moisture damage leading to paper damage.

And, of course, the foil. As above, without the wax.

And, there are multiple sites dedicated to reproducing these beasts for audiophile/phool purposes. Go figure.

Peter Wieck
Melrose Park, PA

On Wednesday, April 26, 2017 at 8:28:19 AM UTC-4, wrote:
On Tuesday, April 25, 2017 at 10:34:46 PM UTC-4, Clifford Heath wrote:
What fails outside of paper capacitors is that anyone still gives a ****.

On Wed, 26 Apr 2017 05:28:17 -0700 (PDT), "
wrote:

There is that. But, let's start with the wax: A mixture of beeswax (small amount),
paraffin, and petroleum jelly for handling. Does anyone here know how old pure
beeswax candles were made? Beeswax was dissolved in warm water, and the
wicks were dipped multiple times into the solution, picking up a bit of additional
wax each time. the keyword is *DISSOLVED*. Even paraffin wax holds water,
and beeswax is directly water-soluble.

I know a woman who does historical re-enactments. One of her things is
making candles. You are right, the wicks are dipped in pure beeswax,
(Many times), and each time they get thicker.

I am not sure if you're saying the beeswax is dissolved *IN* the water,
or if you mean the container holding the wax is placed in warm water.
But to clearify this, there is NO WATER *IN* with the beeswax.

Melting the container of wax with the container in some warm water would
likely work. Although she melts her container over a bed of hot coals,
which were created by burning wood inside a shallow hole in the ground,
surrounded by rocks. There is an iron grill across the rocks, and she
has a tin pan between the wax container and the grill (to keep wax from
dripping into the fire).

It's a simple but time consuming process. She says the main thing is to
keep the temperature right, so the wax stays melted, but dont overheat.
That's all accomplished by the spacing between the coals and the wax
pot, as well as the coals themselves.

At least now I know what wax is used, (or combination of). The petroleum
jelly (vaseline) part seems kind of bizarre, and why that helps with
"handling" makes no sense to me. But I'll take your word for it.

So, now we know how water molecules can migrate thru the wax. But that
dont explain how they get inside of those old plastic coated caps,
(called bumblebees), or similar old caps. Those are sealed real well,
unless they develop a crack.

On Wednesday, April 26, 2017 at 12:20:38 PM UTC-4, wrote:

Huh, Well doesn't a paper cap add that certain 'crispness' to the sound? :^)


As in "burnt to a.... "?

Peter Wieck
Melrose Park, PA

On 4/26/2017 12:33 PM, wrote:
So, now we know how water molecules can migrate thru the
wax. But that dont explain how they get inside of those
old plastic coated caps, (called bumblebees), or similar
old caps. Those are sealed real well, unless they develop
a crack.

They are NOT "sealed real well."
Nor are the old "Micamold" paper dielectric capacitors.

I just re-capped a Collins R-390A receiver. There are 28
paper dielectric capacitors in the one I worked on. About
20 of them were the Sprague bumble bee types, and the rest
were Sprague Vitamine-Q.

Go ahead and say it, "Collins! Top of the line! Mil-Spec!"
They were still crap capacitors




--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

---
This email has been checked for viruses by AVG.
http://www.avg.com

Note the interpolations:

On Wednesday, April 26, 2017 at 2:36:01 PM UTC-4, wrote:
On Wed, 26 Apr 2017 05:28:17 -0700 (PDT), "
wrote:

There is that. But, let's start with the wax: A mixture of beeswax (small amount),
paraffin, and petroleum jelly for handling. Does anyone here know how old pure
beeswax candles were made? Beeswax was dissolved in warm water, and the
wicks were dipped multiple times into the solution, picking up a bit of additional
wax each time. the keyword is *DISSOLVED*. Even paraffin wax holds water,
and beeswax is directly water-soluble.

I know a woman who does historical re-enactments. One of her things is
making candles. You are right, the wicks are dipped in pure beeswax,
(Many times), and each time they get thicker.

I am not sure if you're saying the beeswax is dissolved *IN* the water,
or if you mean the container holding the wax is placed in warm water.
But to clearify this, there is NO WATER *IN* with the beeswax.

In the systems I have observed, the wax is mixed into the warm water, and for the most part floats on top - Little actually dissolves, and what does may be partially oxidized material. But there is definitely some that does. What this method does is allow a very thin layer of wax (as little as two inches) will allow full dipping once the wicks have their first coat. The old farmer that demonstrated this to me explained that it was much safer than putting a separate container in water, or, especially, over a fire.

Melting the container of wax with the container in some warm water would
likely work. Although she melts her container over a bed of hot coals,
which were created by burning wood inside a shallow hole in the ground,
surrounded by rocks. There is an iron grill across the rocks, and she
has a tin pan between the wax container and the grill (to keep wax from
dripping into the fire).

It's a simple but time consuming process. She says the main thing is to
keep the temperature right, so the wax stays melted, but dont overheat.
That's all accomplished by the spacing between the coals and the wax
pot, as well as the coals themselves.

At least now I know what wax is used, (or combination of). The petroleum
jelly (vaseline) part seems kind of bizarre, and why that helps with
"handling" makes no sense to me. But I'll take your word for it.

It does make sense if you consider the need to make a stable material that is easily spread, and spread very thin, and does not go soft at hand-temperatures (which are generally much lower than the typical tube radio. Paraffin makes the hard base, but does not spread well and needs to be quite hot to melt fully. Beeswax gives the spreading properties, but gets soft, so is used in small quantities. Petroleum jelly (thick, pure oil) prevents the materials from clouding and also reduces sticking to the processing machinery, operating at high speed, mostly. Keep in mind that both the beeswax and the jelly are minor admixtures,

So, now we know how water molecules can migrate thru the wax. But that
dont explain how they get inside of those old plastic coated caps,
(called bumblebees), or similar old caps. Those are sealed real well,
unless they develop a crack.

This is an easy one. A 'bumblebee' cap seal relies on the interface between two dissimilar materials with vastly different coefficients of expansion. Plastic and metal. Over time, micro-cracks will develop at the leads. Keep in mind that these capacitors live in a tough environment, and can go from freezing to very hot quickly and repeatedly.

The failure mechanisms are common, well understood, and time-sensitive - far shorter than "today". Unless you dabble in instrument amps, meaning that your caps serve as inductors, resistors, and occasionally as capacitors, you have no business leaving these beasts inside anything expected to function.

Peter Wieck
Melrose Park, PA

analogdial wrote:


1) Cellouse is marvelously hydrgroscopic. It sucks up humidity like a
sponge. Wet cellouse is conductive. There's no reason to overthink
this. Also, don't assume the paper the manufacturers used was stored
or wound in perfectly dry conditions. That's nearly impossible. I have
no doubt caps made under humid conditions failed more quickly than
caps made during dry times.

2) Wax is NOT a perfect seal against moisture. I'm sure plastics are
better but they aren't perfect, either. Ever see a tupperware container
sweating from the inside? That moisture diffused it's way through the
polyethelyne in maybe a few days or even hours.

Paper caps from the old days that HAD to last a long time were sealed
in soldered metal cans in oil. Too expensive for consumer gear! The
engineers who designed this stuff KNEW the paper caps would be failing
in a few years. So what? Electronics changes fast and the buyer
would almost certainly buy something newer before deteriorating caps
killed the device.


Those oil filled bathtub caps failed, as well. The paper broke down,
just like waxed caps, plus the rubber plugs would harden, crack and leak
oil.

--
Never **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)

Michael A. Terrell wrote:


sponge. Wet cellouse is conductive. There's no reason to overthink
this. Also, don't assume the paper the manufacturers used was stored
or wound in perfectly dry conditions. That's nearly impossible. I have
no doubt caps made under humid conditions failed more quickly than
caps made during dry times.


Yes they do and we are seeing the failures now. But it's been a pretty
good run for a paper dielectric cap. Much better than the wax covered
caps.

On 4/27/2017 11:26 AM, analogdial wrote:
Yes they do and we are seeing the failures now. But it's been
a pretty good run for a paper dielectric cap.
Much better than the wax covered caps.

Who are you kidding? Paper caps were already failing after ten
years of service.
The Sprague "bumble bees" and Black Beauty capacitors were
already known failures by the '60s.



--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

---
This email has been checked for viruses by AVG.
http://www.avg.com

OP
also consider in many tube applications the coupling cap has plate voltage on
one side like 250V and feeds a 100k grid resistor on the other side.

It doesn't take much leakage to upset the grid voltage.

m