Question re: coil wire anchoring

[SurreyNick]

I observe in most cases regarding tuning coils the wire from the end of the winding is threaded through one hole in the former and back out through an adjacent one. Quite straightforward.

I wonder however, what adverse effect, if any, would be caused by looping it back through the first hole again so the wire end finishes up inside the former?

I have drawn a picture (attached) which I hope shows what I describe.

Any knowledge on the matter would be much appreciated as I am winding some coils and I want the wires to end up coming through to the inside of the former.

I could of course just have one hole to thread the wire through but I then have a problem anchoring it.

Thanks

Nick

[Kala_12]

You could pass the end in, out and back in through a row of three holes.
Stuart.

[Dickie]

I'm inclined to say no difference at all. The only problem could be reduced reliability, as there is a greater chance of fracturing the wire at that point due to the bend radii. As for anchoring the wire with one pass through the hole how about a dab of varnish or superglue?

[Restoration73]

To anchor and protect the winding, I use heat shrink sleeving.

[SurreyNick]

Thanks for the suggestions. It isn't just a case of anchoring however, I am genuinely interested to know how looping the wire as described might affect selectivity and sensitivity, if at all. Interesting to hear it's unlikely to have an adverse effect.
Nick

[Station X]

You could thread some thicker wire through the holes and connect the thinner winding to it.

[wireful3]

I would guess that in practical terms, compared with other things it would have little effect on the performance of the coil. As others have said mechanical aspects would be more of a problem. I have actually seen coils with three holes for anchoring but in these cases the wire was looped round one pair again to bring it to the outside of the former. What you propose is the same thing.

[SurreyNick]

Swell. Thanks for the replies.

Having given it some thought I will either do one hole and anchor the wires with plugs glued in place, or I'll do two holes with the wire looped through. One final question if anyone can help...

I am using enamelled wire for the windings. How important is it that the trailing wire leads of the two coils don't touch each other or themselves?

I have a reaction coil mounted inside the MW coil former and it can be adjusted up and down a threaded rod, so the trailing leads of this reaction coil need to be slack. There is a risk the trailing wires might touch (short circuit) themselves or come into contact with the trailing wires of the MW coil. Is this likely to cause a problem?

I'd rather not sleeve the wires if I can avoid it as it's likely to make them stiff creating stress in the wire where the sleeving ends, and there is a small possibility it might interfere with the smooth action of the mechanism too.

Thanks

Nick

[wireful3]

Nick, Some early radios had variometers with rotating coils inside the main coil and these usually had tags on the moving coil that were connected to the rest of the set by insulated flexible wires. I think that some of the more recent enameled wires have a much more robust coating. The effect of touching is not likely to cause short circuits but capacity coupling may occur though the importance will depend on frequency.

I have built crystal sets where I moved the coils to adjust the coupling. They were wound with enameled wire and did not give any short circuit problems over a year or so but then they were not adjusted very often.

[SurreyNick]

John that's most helpful, thank you. My coils arrangement is somewhat akin to a simple variocoupler, but mounted vertically and only the proximity of the reaction coil to the MW coil is variable. As you can probably appreciate it won't be adjusted very often. Initially on set-up and alignment, then perhaps if one of the variables of the set change - it's a regenerative TRF so from time to time may need some tweaking.
Nick

[G6Tanuki]

When I've wound coils my usual approach has been to fit a loop of heavy-gauge wire [16 or 18ga] at each end and then solder the actual windings to these anchors. Essentially, use the 'loops' as terminal-posts. This way it's a lot easier to get the coil-winding to stay nice and tight on the former.

Another hint: before winding, put the former in the freezer and heat the wire in the oven. This shrinks the former and stretches the wire - then when you wind the coil and everything returns to room-temperature the former will expand slightly and the wire shrink - so keeping the coil nice and tight.

[SurreyNick]

What excellent advice, on both counts.
Thanks
Nick

[SurreyNick]

Mmm. Apologies. In post #10, I described my coil as a simple variocoupler. I meant loose coupler. Sorry for any confusion caused.
Nick

[G6Tanuki]

A couple more useful tricks:

If your coil needs the windings to be spaced rather than tightly 'close-wound' you can wind a length of nylon fishing-line alongside the main winding to provide accurate spacing. When you've anchored the ends unwind the fishing-line.

Once you've wound the coil it's a good idea to fix it in place. My preferred fixative is made by dissolving a quantity of polystyrene packaging-chips in an eggcupful of petrol and then lightly brushing this over the coil.

When it dries it will anchor the windings rather firmly to the coil-former.

Polystyrene has the dual advantages of being 'low-loss' at radio-frequencies and also does not harbour dampness. It's a lot better than the traditional coil-coatings such as paraffin-wax or Shellac.

[SurreyNick]

Ah, now that's interesting! How does the dissolved polystyrene look when dry? Is it opaque, or completely clear? Do you have a pic you could post of a coil you've wound on clear acrylic and coated in this way so I can see how it appears?
Thanks
Nick