Wax covered capacitors from the 1950s

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.

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

TCC

it

50Kohm.

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?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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

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

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 wrote:

TCC

it

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.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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

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

-- Stephanie Weil New York, USA

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

Regards,

Phil Nelson Phil's Old Radios

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.

Fred McKenzie wrote:

460, TCC

Is it

50Kohm.

paper

equipment

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.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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.

-- Gary E. Tayman/Tayman Electrical Sound Solutions For Classic Cars

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.

n cook wrote:

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

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. ;)

-- Stephanie Weil New York City, USA

Hi John,

Restructuring the website. Will be done in a few dayz. You can still access the previous interface here:

Syl