solidifying toroid core position and windings?

[Jake T]

I just finished making up a multi order HF band pass filter for one of
my ham radio bands. A friend wants me to make one up and send it to him
too. I'm leary of this because I used toroid cores. During shipping, I
can imagine them coming detached or otherwise losing their tuning
because the windings move around from the bouncing around during
transit. I have some quick, 1 hour, two part epoxy here made for PC
use. Could I carefully "paint" each toroid, windings and some epoxy
between toroid and circuit board so it also won't move? Need a quick,
easy, and effective solution. I wouldn't think the clear, two part
epoxy would affect Q or tuning, or would it?

Thank you!

[Fox's Mercantile]

On 2/10/22 3:54 AM, Jake T wrote:
> I have some quick, 1 hour, two part epoxy here made for PC use.

This is the correct stuff to use.
https://shopintertex.com/gc-electronics-10-3702-q-dope-bottle-with-brush-2-fl-oz.html


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

[amdx]

 I have used polystyrene dissolved in Acetone. Best if you can find
crystal styrene like used in parts drawers.

It will dissolve... slowly.

But I started with polystyrene foam dissolved in acetone.

 I have a 4" coil I used this on well over 10 years ago and it it still
holding up.

                                   Mikek


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[Jeff Liebermann]

On Thu, 10 Feb 2022 04:54:15 -0500, Jake T <jake...@steak.com>
wrote:

If your toroidal inductors are wound that loose, you'll have damage in
shipping, mostly from the enamel coating falling off from vibration.
Some kind of conformal coating will help.
<https://www.chemtronics.com/the-ultimate-guide-to-conformal-coating>
Before selecting any coating, lookup the loss tangent values and see
if it will get hot due to RF losses. If you're not sure, coat a PCB
with the coating, let it dry, and bake it in a microwave oven. If it
tends to crumble, burn, melt, or otherwise self destruct, find
something with less loss. 1kW at 2.4GHz is a rather brutal test for a
coating that only needs to work up to 30MHz, but is quick and easy. If
it survives at 2.4GHz, it will work at 30MHz.

If the BP filter is designed using high Q inductors and mechanical
vibration detunes these inductors, your design is faulty and you will
have other problems, such as multiple problems caused by water. I
used to design marine radios and quickly learned that high-impedances,
high-Q tuned circuits, and high voltages were really bad ideas in a
marine environment. So, we designed most everything using low
impedances, low-Q tuned circuits, and low voltages. The result was
that the radio worked nicely when wet and did not require any kind of
coating. Such coatings are a mess to apply and handle. Rework is
either difficult or impossible.

Here's an example from about 1980. This is the Intech Inc Mariner
3600 150w PEP SSB HF marine radio:
<https://ce3dr.files.wordpress.com/2016/12/img_1630.jpg>
<https://ce3dr.files.wordpress.com/2016/12/img_1631.jpg>
<https://ce3dr.files.wordpress.com/2016/12/img_1632.jpg>
<https://www.hellocq.net/forum/read.php?tid=226493>
The large board full of toroidal inductors are the TX/RX LP (low pass)
filters. We didn't use or need BP (band pass) filters. Notice the
lack of any conformal coating. I will admit that we did use some wax
to keep the synthesizer VCO from becoming microphonic. It was also
one of the few circuits that were sensitive to moisture.

Good luck.

--
Jeff Liebermann je...@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558

[Jake T]

This is exactly what I ended up doing, dissolving foam in acetone. It
didn't mix the greatest as I should probably have used a different
solvent, like ethyl acetate, but it got the job done. And I still have
plenty left over in a sealed jar.

[Jake T]

Thanks for the info. I should have mentioned that this was for a
receiver and will never be used for a transmitter. I ended up making
the poly glue myself using white foam dissolved in acetone. Works fine.
Took about 8 hours to fully dry. Very sold result and non-conductive.

[Jeff Liebermann]

On Sun, 13 Feb 2022 07:55:55 -0500, Jake T <jake...@steak.com>
wrote:
(chomp)

>Thanks for the info. I should have mentioned that this was for a
>receiver and will never be used for a transmitter. I ended up making
>the poly glue myself using white foam dissolved in acetone. Works fine.
> Took about 8 hours to fully dry. Very sold result and non-conductive.

You may have goofed. If you are using enamel, lacquer or shellac
insulated copper "magnet" wire for winding your coils, the acetone
solvent will dissolve the insulation. I suspect the reason you
observed a "solid result" is because the "melting" insulation has now
glued itself to the insulation on adjacent turns. That's pretty good
if you can keep it from moving, but since dissolving the insulation
also makes it thinner, I suspect that any movement will cause
intermittent shorted turns.

Hint: Check a chemical resistance chart for whatever you're using for
insulated wire before using any solvents:
"Enameled Wire Insulation Characteristics"
<https://mwswire.com/insulation-characteristics/>

Before wave soldering machines switched from using chlorinated
hydrocarbon solvents to clean off solder flux (about 1974), to aqueous
(water) based cleaning solutions, we used to use vapor degreasers
loaded with trichlorethylene solvent to clean PCB (printed circuit
boards), which included the boards full of PE (plain enamel) magnet
wire wound torroidal inductors (as shown in the M3600 photos I
previously linked). We had to use a special insulated magnet wire AND
keep the temperature very low in the vapor degreaser, in order to not
soften the insulation. We also had to learn not to touch the coils
until the PCB was dry and at room temperature. Polyurethane based
insulations were better but still required some care.

[Jake T]

On 2/13/22 20:31, Jeff Liebermann wrote:
> On Sun, 13 Feb 2022 07:55:55 -0500, Jake T <jake...@steak.com>
> wrote:
> (chomp)
>
>> Thanks for the info. I should have mentioned that this was for a
>> receiver and will never be used for a transmitter. I ended up making
>> the poly glue myself using white foam dissolved in acetone. Works fine.
>> Took about 8 hours to fully dry. Very sold result and non-conductive.
>
> You may have goofed. If you are using enamel, lacquer or shellac
> insulated copper "magnet" wire for winding your coils, the acetone
> solvent will dissolve the insulation. I suspect the reason you
> observed a "solid result" is because the "melting" insulation has now
> glued itself to the insulation on adjacent turns. That's pretty good
> if you can keep it from moving, but since dissolving the insulation
> also makes it thinner, I suspect that any movement will cause
> intermittent shorted turns.
>
> Hint: Check a chemical resistance chart for whatever you're using for
> insulated wire before using any solvents:
> "Enameled Wire Insulation Characteristics"
> <https://mwswire.com/insulation-characteristics/>

Ah, good points here! I wondered about using acetone from the start,
should have checked this further. Well, pretty hard to test the toroids
in circuit now as there are caps across them, so I placed an identically
wound spare in acetone for a few hours just to see what occurs.

I see the MSDS for the actual Q Dope is a mix of the poly and MEK. I
was going to go with that formula at first, but I only had acetone on
hand and I can't seem to find MEK locally. There's something called MEK
substitute and the MSDS for that seems to indicate that it is ethyl
acetate. I can get the substitute, but then the question becomes whether
or not the ethyl acetate would dissolve the enamel. I used to use pure
ethyl acetate in the past to euthanize insects as entomology used to be
one of my hobbies. So it, like acetone, can be quite potent.

[Jake T]

Well, the good news is that the enamel wire wound toroid I placed in
acetone for 8 hours showed no signs of breaking down. I feel confident
that the filter coatings are ok. That's about how long they took to dry
in the circuit. However, the points you made here I won't forget soon
in case I run into a questionable future wire.