Nail polish as coil dope??

Nail polish as coil dope??

Post by Yin Lung Sh » Thu, 09 May 1996 04:00:00


Quick question -

Is clear nail polish (apparently composed of two kinds of acetate and
solvent) acceptable as coil dope?  I'm building a project and thought
I had read somewhere that it was so I used some on four coils.  I checked
the inductances and they measured the same before and after, but I wasn't
able to check for possible Q degrading effects.  After I soldered the
coils in, I got some real Q-dope.  Now I'm wondering if I should pull
those coils and rebuild them. Any comments?

Yin Shih, KO6VY, PP-ASEL-IA

 
 
 

Nail polish as coil dope??

Post by WB3 » Fri, 10 May 1996 04:00:00



Quote:>Is clear nail polish (apparently composed of two kinds of acetate and
>solvent) acceptable as coil dope?  I'm building a project and thought
>I had read somewhere that it was so I used some on four coils.  I
>checked the inductances and they measured the same before and after,
>but I wasn't able to check for possible Q degrading effects.  After I
>soldered the coils in, I got some real Q-dope.  Now I'm wondering if
>I should pull those coils and rebuild them. Any comments?

Rebuilding those coils would be a major waste of time.  Fingernail
polish work just fine for this.  Its only drawback is that it may not
adhere as well as an actual adhesive, and it tends to be brittle.  If
you used enough so that it soaked into the coil, between the turns,
neither of these characteristics is likely to cause a problem.

73,
Jack  WB3U

 
 
 

Nail polish as coil dope??

Post by un.. » Sat, 11 May 1996 04:00:00


>Quick question -
>Is clear nail polish (apparently composed of two kinds of acetate and
>solvent) acceptable as coil dope?  I'm building a project and thought
>I had read somewhere that it was so I used some on four coils.  I checked
>the inductances and they measured the same before and after, but I wasn't
>able to check for possible Q degrading effects.  After I soldered the
>coils in, I got some real Q-dope.  Now I'm wondering if I should pull
>those coils and rebuild them. Any comments?
>Yin Shih, KO6VY, PP-ASEL-IA


Old trick I used for many years.  But can't say specifically
what it would be like at UHF and above, especially if any
power were involved.  DON'T fire any r.f. into it before it dries!

Uncle Brian  VK6BQN

 
 
 

Nail polish as coil dope??

Post by Siegfried Rambau » Mon, 13 May 1996 04:00:00


> >Is clear nail polish (apparently composed of two kinds of acetate and
> >solvent) acceptable as coil dope?

NOPE ... The solvent is acetone, highly flammable and toxic

The thing you could do, however, is looking at your local library for
some real olden radio builder's book. I was amazed, how old some of the
stuff is, they have at my local library. In those real old books, you
might find some recipes for what you need.

Quote:> adhere as well as an actual adhesive, and it tends to be brittle.

... cause it is not made for coils, but for fingernails

Quote:> you used enough so that it soaked into the coil, between the turns,
> neither of these characteristics is likely to cause a problem.

When you soak it, you might change the dielectricum and -- though
unlikely to have much influence --- the coils might change in frequency
response ...
 
 
 

Nail polish as coil dope??

Post by Roy Lewall » Tue, 14 May 1996 04:00:00




>> >Is clear nail polish (apparently composed of two kinds of acetate and
>> >solvent) acceptable as coil dope?

>NOPE ... The solvent is acetone, highly flammable and toxic

>The thing you could do, however, is looking at your local library for
>some real olden radio builder's book. I was amazed, how old some of the
>stuff is, they have at my local library. In those real old books, you
>might find some recipes for what you need.
>. . .

Coil dope is typically made by dissolving polystyrene in acetone, so "real"
coil dope is also highly flammable and toxic until it dries. You can make
it yourself quite easily with styrofoam and acetone from the paint store,
but do handle it and the acetone carefully. As Siegfried said, it's very
flammable.

I never have figured out how applying coil dope would improve a coil. The
best quality dope will degrade the Q by decreasing the apparent inductance
due to increased capacitance. Many other materials used for dope will
introduce loss as well. Maybe someone could enlighten me.

Roy Lewallen, W7EL

 
 
 

Nail polish as coil dope??

Post by Jim » Tue, 14 May 1996 04:00:00


>I never have figured out how applying coil dope would improve a coil.

The only purposes I've been able to figure out are that it keeps the
windings from moving (if touched, or from microphonics), and it seals
the coil and form from humidity in the air.  You WILL see a change in
inductance if your cardboard coil form is sopping wet, has fungus
growing on it, and the powdered-iron slug has gotten rusty....

I haven't measured a change in perfornamce by adding coil dope (and
I have used a wide variety of glues, besides nail polish), but I've
seen significant degradation caused by damage to an unprotected coil.
As in, "Oops, I didn't mean to cut through that 30-ga wire winding..."

Jim N6OTQ

 
 
 

Nail polish as coil dope??

Post by Kelly Gr » Tue, 14 May 1996 04:00:00

: I never have figured out how applying coil dope would improve a coil. The
: best quality dope will degrade the Q by decreasing the apparent inductance
: due to increased capacitance. Many other materials used for dope will
: introduce loss as well. Maybe someone could enlighten me.

As near as I can figure, the only advantage of coil dope is that it
mechanically secures the turns of wire. Without the dope, it is possible
for the wire in a loosely wound coil to shift, changing the coil inductance.

This is probably best prevented by winding the coil turns as tightly as
possible, and as neatly as possible, thus making it difficult for any
movement of the wire. If the coil is wound with small diameter wire, a
drop or two of adhesive securing the ends of the coil is probably a good
idea.

     <o_o>


 
 
 

Nail polish as coil dope??

Post by Terry Fuga » Tue, 14 May 1996 04:00:00





>>> >Is clear nail polish (apparently composed of two kinds of acetate and
>>> >solvent) acceptable as coil dope?

>>NOPE ... The solvent is acetone, highly flammable and toxic

>>The thing you could do, however, is looking at your local library for
>>some real olden radio builder's book. I was amazed, how old some of the
>>stuff is, they have at my local library. In those real old books, you
>>might find some recipes for what you need.
>>. . .

>Coil dope is typically made by dissolving polystyrene in acetone, so "real"
>coil dope is also highly flammable and toxic until it dries. You can make
>it yourself quite easily with styrofoam and acetone from the paint store,
>but do handle it and the acetone carefully. As Siegfried said, it's very
>flammable.

>I never have figured out how applying coil dope would improve a coil. The
>best quality dope will degrade the Q by decreasing the apparent inductance
>due to increased capacitance. Many other materials used for dope will
>introduce loss as well. Maybe someone could enlighten me.

>Roy Lewallen, W7EL

I do not think that the "dope" is to improve any quality of the coil,
but, instead, just to hold the wires in place.  If the wires are not
"fixxed" then the L can varry, especialy with any sort of mechanical
shock or vibration.  The dope could also keep water off the wires.
I had some dew ruin a nice home made vfo when the litz wire got wet.
 
 
 

Nail polish as coil dope??

Post by WB3 » Tue, 14 May 1996 04:00:00

I recently wound a plate ***for a linear amplifier using 26 gauge
magnet wire on a ceramic form.  After it was wound, I gradually
removed turns from one end so that the internal series resonances of
the ***didn't fall on any of the ham bands.  The ***ended up
with resonances at about 26.5 MHz, 33 MHz, and several others above
that frequency.  The highest I measured (with a GDO) was about
120 MHz.

When the adjustment was complete, I secured the loose end of the coil
with a dab of superglue, then I dipped the whole coil in polyurethane
varnish.  After the varnish dried, I went back and checked all the
resonances again.  If anything had changed as a result of the varnish,
it wasn't detectable by any means I had available.

For the ultimate in protection, a coil like this could also be soaked
or "painted" with polyester resin or epoxy.  Both of these are used as
the base in fiberglass, so the effect on Q should be minimal.

73,
Jack  WB3U

 
 
 

Nail polish as coil dope??

Post by Ed Gang » Tue, 14 May 1996 04:00:00


>I never have figured out how applying coil dope would improve a coil. The

1. AS others have pointed out, it is good for mechanical stability.
2. Most coil dope is very good at high voltage, as well. So if you
are generating lotsa volts in your coil/xfmr then it helps (only helps)
prevent arc-over between a lo voltage and a high voltage area on your
coil.
Regards,
Ed
 
 
 

Nail polish as coil dope??

Post by Roy Lewall » Wed, 15 May 1996 04:00:00



Quote:>. . .
>For the ultimate in protection, a coil like this could also be soaked
>or "painted" with polyester resin or epoxy.  Both of these are used as
>the base in fiberglass, so the effect on Q should be minimal.

Years ago I tried coating a toroid coil (wound on type 6 powdered iron, of
Q about 250 as I recall) with various materials and measuring the change in
Q. I don't have the notes any more but recall that all but a few materials
noticeably degraded the Q, some badly. Ordinary epoxy glue, as I remember,
significantly reduced the Q. I wouldn't expect this to present a problem
with an RF choke. But I wouldn't use it for coils intended for an
oscillator tank, filter with high loaded Q, or other application where Q is
critical.

Roy Lewallen, W7EL

 
 
 

Nail polish as coil dope??

Post by Tom Randol » Thu, 16 May 1996 04:00:00


>I haven't measured a change in perfornamce by adding coil dope (and
>I have used a wide variety of glues, besides nail polish), but I've

Well, for what it's worth, I've measured the Q of toroids dipped in plain old
polyurethane varnish, the kind you'd finish furniture with, and it has a fairly
insignificant effect at about 10 MHz or less.

The only advantage I know of is mechanical stabilty, which might matter if the
rig is subject to vibration or shock. Sort of similar to dripping beeswax on
your coil slugs, I guess.

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