Wax covered capacitors from the 1950s

[n cook]

Proudly stating "British Made"
What makes all those yellow tubular wax covered caps, Dubilier type 460, TCC
type 343, 645 etc 300V to 750V caps in range 1 to 100nF go so leaky ? Is it
the wax is actually hygroscopic and absorbs water vapour over time. ?
On DVM resistance scale in Meg ohms but on a Megger then as low as 50Kohm.

 

[Rheilly Phoull]

Proudly stating "British Made"
What makes all those yellow tubular wax covered caps, Dubilier type
460, TCC type 343, 645 etc 300V to 750V caps in range 1 to 100nF go
so leaky ? Is it the wax is actually hygroscopic and absorbs water
vapour over time. ?
On DVM resistance scale in Meg ohms but on a Megger then as low as
50Kohm.

These were the start of planned obsolescence
My guess is the wax as you say or bad manufacturing process.

 

[Steven]

These were the start of planned obsolescence
My guess is the wax as you say or bad manufacturing process.

--

Cheers ......... Rheilly P

Where theres a will, I want to be in it.

You can't top my nym of Dr. Antichrist PhD though. Well it could be fun
to make a dash at it...

The concept of planned obsolescence was made feasible and completely
successful by the last 40 years of my life.

 

[Paul Sherwin]

Proudly stating "British Made"
What makes all those yellow tubular wax covered caps, Dubilier type 460, TCC
type 343, 645 etc 300V to 750V caps in range 1 to 100nF go so leaky ? Is it
the wax is actually hygroscopic and absorbs water vapour over time. ?
On DVM resistance scale in Meg ohms but on a Megger then as low as 50Kohm.

Yes, the wax is hygroscopic. The problem isn't restricted to British caps,
most non-tropicalised consumer grade paper caps from the 40s and 50s will
be leaky now.

Paul

 

[n cook]

50Kohm.

Yes, the wax is hygroscopic. The problem isn't restricted to British caps,
most non-tropicalised consumer grade paper caps from the 40s and 50s will
be leaky now.

Paul

If they were not wax covered would they still have been be problematic ?
Understandable in a damp environment but indoors would dampness get in the
paper and not evaporate again if not waxed, the use of wax sealing the
dampness/vapour/condensate insde each cap?

 

[Syl]

Yes, the wax is hygroscopic. The problem isn't restricted to British caps,
most non-tropicalised consumer grade paper caps from the 40s and 50s will
be leaky now.

Paul

ALL paper caps go bad with time, whether they are "tropicalized" or sealed
like the infamous Black Beauty.

Oil caps on the other hand have a pretty good lifetime. I have a Russian
made radio and the sealed oil caps are still good.
There are no paper/wax caps in that radio. Parts are military grade, and I
mean military grade.

Syl

 

[Michael A. Terrell]

If they were not wax covered would they still have been be problematic ?
Understandable in a damp environment but indoors would dampness get in the
paper and not evaporate again if not waxed, the use of wax sealing the
dampness/vapour/condensate insde each cap?

Some of the wax boils away over time, and they made the capacitors
out of what was available at the time. Thermal cycling will let
moisture into the capacitor as the coating starts to break down.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[nesesu]

The leakage is not an issue of moisture migrating into the capacitor
'jellyroll' slug directly, but once there is some moisture in the slug
in combination with the sulphites in the kraft paper, they promote
aluminum ions of the foil in the slug to begin to migrate into the
paper dielectric. These ions eventually cause leakage paths to form
through the paper, or worse, cause a moderately high conductive path
that, with a high bias voltage, will cause it to carbonize and cause a
high leakage path or full short. If the cap moves to a dry location the
moisture theoretically will migrate out again, but the ionic migration
does not reverse--just slows down.
The "tropical" wax that I use in paper cap rebuilding may be somewhat
better than the 'filled' potting and slug waxes of consumer grade paper
caps, but it's main difference is the anti-fungicides it contains to
delay the formation of molds and mill-dew on the organic components.

Neil S.

 

[n cook]

The leakage is not an issue of moisture migrating into the capacitor
'jellyroll' slug directly, but once there is some moisture in the slug
in combination with the sulphites in the kraft paper, they promote
aluminum ions of the foil in the slug to begin to migrate into the
paper dielectric. These ions eventually cause leakage paths to form
through the paper, or worse, cause a moderately high conductive path
that, with a high bias voltage, will cause it to carbonize and cause a
high leakage path or full short. If the cap moves to a dry location the
moisture theoretically will migrate out again, but the ionic migration
does not reverse--just slows down.
The "tropical" wax that I use in paper cap rebuilding may be somewhat
better than the 'filled' potting and slug waxes of consumer grade paper
caps, but it's main difference is the anti-fungicides it contains to
delay the formation of molds and mill-dew on the organic components.

Neil S.

Proudly stating "British Made"
What makes all those yellow tubular wax covered caps, Dubilier type 460, TCC
type 343, 645 etc 300V to 750V caps in range 1 to 100nF go so leaky ? Is it
the wax is actually hygroscopic and absorbs water vapour over time. ?
On DVM resistance scale in Meg ohms but on a Megger then as low as 50Kohm.

Strange thing this mold/midew stuff, this is one of the strangest fault
causes I've ever had

Scopex 14D10 scope
Nasty noise from the ps and nothing else.
Using an isolation transformer and observing on a scope
there was low level oscillation of the smps and one burst of
oscillator per cycle of the mains.This smps is the type with
the oscillator on the mains side of the pulse transformer.
All active components seemed ok and no leaky caps.
Putting a dc supply across the oscillator and varying
the voltage the drive to the main trannie changed state
at about 20V.Disconnecting the pulse transformer and
testing with a megger (high v insulayion tester) there
was no interwinding breakdown and the inductance of
the coils looked right (no shorted turns).Eventually found
the O/P was being loaded by a faulty opto-isolator that
gates the beam current.It was ohmic between I/P
and O/P so removed and cracked open with mole grips
(vice grip locking pliers).Looking at the transparent
bridge under a 30x microscope there were tiny circles of
mold or fungus that had grown and coalesced forming
a resistive bridge between I/P and O/P.

 

[Fred McKenzie]

Proudly stating "British Made"
What makes all those yellow tubular wax covered caps, Dubilier type 460, TCC
type 343, 645 etc 300V to 750V caps in range 1 to 100nF go so leaky ? Is it
the wax is actually hygroscopic and absorbs water vapour over time. ?
On DVM resistance scale in Meg ohms but on a Megger then as low as 50Kohm.

N. Cook-

Neil pegged it. It isn't the wax that is hygroscopic as much as the paper
used as a dielectric in such capacitors made until the late 50s.

As a teenager, I had collected boxes of components by canibalizing
equipment from a local Radio-TV repairman's trash bin. When I saved up
enough money to buy a multimeter, I found that over 90 percent of the
paper capacitors were leaky, and may have been the cause of the equipment
failure. I learned quickly that the first step in repairing old radios,
was to replace all the paper capacitors.

Somewhere around 1957, the capacitor companys started using plastic
dielectric, sometimes in combination with paper. Names like "Mylar",
"Dipped Mylar" and "Paper-Mylar" were used to describe these newer
capacitors. From my viewpoint, that marked a turning point in the
reliability of electronic circuits.

I understand that some people who restore antique radios, will use the
case of a paper capacitor, replace the core with a mylar capacitor and
seal it again with wax.

Fred

 

[Stephanie Weil]

The leakage is not an issue of moisture migrating into the capacitor
'jellyroll' slug directly, but once there is some moisture in the slug
in combination with the sulphites in the kraft paper,

I wonder if this is part of what kills a supposedly better-sealed
"Black Beauty" (paper cap sealed in a molded plastic capsule)?

 

[Phil Nelson]

I understand that some people who restore antique radios, will use the

case of a paper capacitor, replace the core with a mylar capacitor and
seal it again with wax.

For more details on capacitor replacement (including restuffing), you can
read:

http://antiqueradio.org/recap.htm

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

 

[nesesu]

Fred, if you are interested, I can send a series of photos showing the
process I use in restuffing old cardboard cased paper caps and a new
process I use to make brand new cardboard cases, since I am running out
of old cap cases in some sizes, to restuff.
It is really annoying when recapping a worthwhile set to find that 3 or
4 original cardboard cased caps have been replaced with plastic or
ceramic cased replacements that are bad, but cannot easily be cleaned
out for restuffing and are, in any case, non-OEM, so I developed a
simple method of making new shells of any regular size.

Neil S.

 

[n cook]

Fred, if you are interested, I can send a series of photos showing the
process I use in restuffing old cardboard cased paper caps and a new
process I use to make brand new cardboard cases, since I am running out
of old cap cases in some sizes, to restuff.
It is really annoying when recapping a worthwhile set to find that 3 or
4 original cardboard cased caps have been replaced with plastic or
ceramic cased replacements that are bad, but cannot easily be cleaned
out for restuffing and are, in any case, non-OEM, so I developed a
simple method of making new shells of any regular size.

Neil S.

I suppose there is a cottage industry of taking modern 0.5,1,2W metal oxide
resistors, molding in a fire cement wrapper and then painting with
resistance colour-code bands.

 

[Gary Tayman]

In regards to these "cottage industries", is there anybody out there selling
"new" OEM resistors and capacitors?

Among my many, many future projects is my Atwater Kent 60. In the process
of fixing it up, just about all the carbon resistors have been replaced.
These are white ceramic with soldered ends. I've kept the old ones, with
the high hopes that one day I'll try to make some sort of reproduction that
can go back in the radio. If somebody is selling these I may be interested.

 

[nesesu]

Actually, I usually paint them with the BED colour code after bending
the leads at a sharp right angle and adding some epoxy on each end to
give the 'dogbone' radial leaded shape.
[BED= Body-End-Dot coding that was common just before the colourbanding
became common.]

Neil S.

Fred, if you are interested, I can send a series of photos showing the
process I use in restuffing old cardboard cased paper caps and a new
process I use to make brand new cardboard cases, since I am running out
of old cap cases in some sizes, to restuff.
It is really annoying when recapping a worthwhile set to find that 3 or
4 original cardboard cased caps have been replaced with plastic or
ceramic cased replacements that are bad, but cannot easily be cleaned
out for restuffing and are, in any case, non-OEM, so I developed a
simple method of making new shells of any regular size.

Neil S.

 

[John Goller, k9uwa]

Syl

Yo Syl ... what happened to your website?.. went to look at your bit about
making new old resistors.. the tech stuff won't work on the site..

John k9uwa

 

[Stephanie Weil]

n cook wrote:
I suppose there is a cottage industry of taking modern 0.5,1,2W metal oxide
resistors, molding in a fire cement wrapper and then painting with
resistance colour-code bands.

Our own Syl Vanier did that. I saw the procedure documented on his
homepage.

That right there convinced me he had totally lost his mind.

 

[Syl]

[email protected]
says...
Yo Syl ... what happened to your website?.. went to look at your bit about
making new old resistors.. the tech stuff won't work on the site..

John k9uwa

Hi John,

Restructuring the website. Will be done in a few dayz. You can still access
the
previous interface here: http://www.oldradioz.com/old_index.html

Syl