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Author Topic: stabilizing a toroid  (Read 1605 times)
VE3VVF
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Posts: 41




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« on: October 20, 2009, 02:23:24 PM »

I am building the Ten-Tec 1340 kit and the VFO toroid is quite sensitive to movements and I want to make it permanent on the frequencies of my choice.  Is there a good way to keep the windings from moving?  Nail polish , glue gun?

Thanks for any suggestions
Scott
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W5FYI
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« Reply #1 on: October 20, 2009, 02:49:05 PM »

The two old-fashioned ways were 1) Q-dope and 2) beeswax. Q-dope (polystyrene+solvent) was used to hold windings in place more-or-less permanently--the solvent evaporates and leaves the hard polystyrene plastic to hold everything together. Beeswax can also be used--it holds up well to moderately-high temperatures, but can be melted if necessary. A lot of sewing goods stores sell it.

I've also used fingernail polish and hot glue with good results. Of the two, I'd favor the hot glue, since it can be remelted to add or remove turns, or change the toroid's orientation. My guess is it would also dampen microphonics somewhat better than fingernail polish alone.
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VE3VVF
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« Reply #2 on: October 20, 2009, 02:52:31 PM »

Wonderful.  Thatns for the info.
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AA4PB
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« Reply #3 on: October 22, 2009, 09:54:21 AM »

Q-dope is still available. Supposedly it has minimal affect on the inductance. Google will get you lots of sources.
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WX7G
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« Reply #4 on: October 23, 2009, 12:17:23 PM »

An old issue of the ARRL Handbook said Q-dope can be made by desolving styrofoam in acetone. Might this harm the wire insulation?

RTV works to secure toroids. A non-corrosive type is used in the electronics industry.

The hot melt glue suggestion sounds like the best way to go.
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W5FYI
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« Reply #5 on: October 24, 2009, 04:34:36 PM »

"... Might this harm the wire insulation?"  It might "melt" some plastic insulation, but it has virtually no effect on the insulation used on magnet wire. Acetone evaporates rapidly, and there might be health issues if too much is inhaled. I've used both acetone and MEK to dissolve styrofoam, and both work well and don't seem to harm PC board components. (MEK is the strong solvent methyl ethyl ketone).
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K2QPN
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« Reply #6 on: October 26, 2009, 09:34:09 AM »

I have been using a dab of hot melt glue. I have done this on several QRP rigs. Works so well that I 'borrowed' one of my wife's glue guns.

73, Bob K2QPN
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VE3WMB
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Posts: 289




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« Reply #7 on: October 27, 2009, 06:33:59 PM »

I raised a similar question about a year ago on the yahoo group for the KD1JV ATS-3A rig. It has separate band modules with 3 or 4 toroids each.
To change bands you must swap modules and I was concerned that this would eventually take it toll on the toroids as a few are wound with #32 AWG. Someone in the group took it upon himself to wind a bunch of toroids and measure their characteristics and then use different methods to secure the toroids to a PCB (most have already been mentioned here in previous responses). He then repeated the measurements, noting any changes in the inductance and Q. The conclusion was that the hot glue method had the least impact on the electrical characteristics of the coil.

The trick that I use was gleaned from the manual for the original KD1JV ALT Tuner kit sold by Hendricks QRP kits. Cut a small sliver of hot glue stick with an exacto-knive and wedge it under the toroid once it is mounted to the board. Heat gently with a heat gun or hair dryer just until
the glue starts to melt, gently push the coil down into the melted glue. Let the board sit for a few minutes until the glue hardens.

Best of luck with your Ten-Tec rig Scott.

Michael VE3WMB
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WB6BYU
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Posts: 13335




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« Reply #8 on: October 27, 2009, 08:37:55 PM »

Another option is to use a nylon bolt, nut and washer to
secure the toroid to the PCB.  Drill a hole in the board,
pass the bolt through the board and the hole in the toroid,
put on the washer and nut and tighten them down.  You can
add a small ring of glue under the washer (or between the
toroid and the board) if you want to make sure the turns
stay in the same places, but in many cases it won't be
necessary.
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AA4PB
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« Reply #9 on: October 28, 2009, 06:17:31 AM »

I wonder how much affect the nylon bolt, hot glue, etc. has on the Q of a torid? Anybody ever do some actual measurements to see?
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HFRF
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Posts: 1




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« Reply #10 on: November 02, 2009, 07:39:58 AM »

Shellac is an excellent transformer coating.  It is still used in coating transformers, circuit boards, and coils / motor windings.  It can be removed by dunking in alcohol.  Shellac will not react with any known paint and shellac can be colored.  I use black shellac to coat transformers.  Shellac also makes a good primer even for aluminum because it sticks to just about anything.  Shellac is not paint, its the secretion from an type of insect.  Shellac is a great water repellent.
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KM3K
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Posts: 322




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« Reply #11 on: November 03, 2009, 10:21:19 AM »

My comments presume the coil in the VFO needs to have high-Q. That said:
1. Stay away from Q-dope for a high-Q coil.
It will significantly lower the coil's Q.
I can not provide you with my test-data as I left the company where I did my tests as a crystal-filter design-engineer.
It is unkind but true to say, "Only a dope would use Q-dope on a high-Q coil."
2. I'm not familiar with your set-up, but if you can lay the coil on the pcb and tap a hole for a nylon-screw, that will be very effective; lay a nylon-washer on top of the coil, then screw the assembly in place. I had success using that approach. On the other side of the pcb, just touch a hot soldering-tip to the screw's threads at the pcb to secure the screw in place.
3. Lastly, RTV is effective in securing a coil to a pcb (degrease the pcb with a Q-tip and isopropyl-alcohol) but place the RTV only around the outside rim; DON'T get any near or in the hole. Normally, the RTV will take a full 24-hours to cure.
73 Jerry KM3K
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WB6BYU
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« Reply #12 on: November 03, 2009, 03:49:57 PM »

I've also mounted toroids and two-hole cores to the PCB
with small tie wraps.  They aren't as good for holding
the individual turns in place, however.
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W6BKY
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Posts: 1




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« Reply #13 on: November 16, 2009, 10:02:50 AM »

Haven't done any lab measurements.  I have, however, used a nylon bolt through a toroid on a VFO in several VFO circuits, and have had no problems.

For additional stability, I usually enclose the toroid in a grounded "cage".  For a VFO, always use a "7" (white) core, as opposed to a "6" (yellow) or a "5" (red).  The "7" mix is thermally more stable.
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