November 2017 63
transmitter back to life. The power
supply uses oil filled capacitors,
which don’t seem to have handy
replacements. Assuming that I can
change the oil to reduce the leakage
current, what kind of oil is used?
Will motor oil work, for example?
#1 I’ve never heard of refilling that
size capacitor, but I do have some
experience with much larger ones.
We had a number of very large
capacitors that our lab received from
a national laboratory as part of a
research project. They originally had
transformer oil as a dielectric but the
outer cases were cracked and it had
leaked out. Because of the problems
at that time with transformer oil
containing high levels of PCBs,
we used castor oil as a substitute
with good results. I have no idea if
motor oil would work but I wouldn’t
#2 Cornell Dubilier manufactures
oil filled AC and DC capacitors. You
can order their products through
numerous electronics distributors.
DC oil filled
AC oil filled
Two additional suppliers of
high voltage capacitors, including
the oil filled type, are www.
plasticcapacitors.com and www.
Also see www.rfparts.com for
many types of radio and transmitter
components including capacitors.
Capacitor technology has
advanced tremendously from
the designs found in old tube
equipment. There could very well
be a suitable modern type of high
voltage electrolytic or metallized
polypropylene film capacitor that will
function correctly in your circuit.
The high leakage current is likely
caused by moisture and/or damage in
the capacitor. Changing the oil is not
likely to help.
Use caution in dealing with
old oil filled capacitors generally
manufactured prior to the mid 1970s.
If they are sealed and working, then
fine. If they are leaking or you are
messing with the internals, know
that they can contain PCB oil which
is claimed to be a health hazard.
Modern oil filled capacitors are of
the non-PCB oil type. Motor oil is
not suitable for filling a capacitor.
Generally, modern oil filled capacitors
use a mineral oil or a silicon oil.
#3 Please do not attempt this.
Many oil filled capacitors used oil
that contained PCBs — a carcinogen.
They should be disposed of as VERY
hazardous waste. PCBs were banned
sometime in the '70s.
A product that I worked with
contained oil filled capacitors and
we had to change over to new types.
It is almost certainly NOT motor oil.
There seems to be a fair number of
antique radio restoration enthusiasts,
so you might try a web search.
Also, just search for the model and
manufacturer of your transmitter. Any
markings on the capacitor will also be
You might look up references to
the American Radio Relay League
(ARRL). They have been the technical
center for amateur radio for a very
long time. If your transmitter is
homemade (homebrew), it might be
one that they described in one of
their handbooks or a QST magazine.
You can probably find a few ARRL
Amateur Radio handbooks (annual
publications) at your local library.
[#8173 - August 2017]
PCB Layout Software
I am a retired Field Service
Engineer. Over a decade and a half
after early retirement from IBM, a
friend asked if an idea he had could
be built. I assured him it could.
He offered me partnership
if I would design and build a
demonstration system. I designed,
built, and programmed a system that
works just like he wanted it to. An
existing patent that I could find no
work-around for expires this year.
We’d like to have systems ready to go
before we start doing demonstrations.
Now, I need to convert my proto-board to a more compact layout to be
mass produced. The problem is that all
the design software I’ve found requires
that work be done online. Not even
a simple schematic design without
being on the Web.
I need recommendations for
offline software to generate a file for
use by a production service. All I’ll
need is a library of templates for basic
TH mounting components. I do not
intend to put the results out in the
clouds because oftentimes, there be
#1 Take a look at KiCad, www.
kicad-pcb.org. Many operating
systems are supported. KiCad is an
open source software suite. If you
download the Footprints Library, you
can work offline. All files are stored
locally on your machine. If you don’t
install the Footprints Library, then
KiCad will connect to the KiCad
GitHub server for the Footprints, but
application files are still stored locally
on your machine.
You can also do some searching
for “using KiCad offline.”
Some information is here to get
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