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Old 14th Mar 2018, 10:39 pm   #1
Jolly 7
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Default Keeping tuning cord attached to spring

A question for experts in restringing broken tuning cords in transistor radios. Often I have found it very awkward to tie a knot to the spring attached to the tuning spindle as it keeps slipping away. There was a bluish glue used in the past to secure the cord. I have not succeeded in using modern glues so far. Are there alternatives ?

Last edited by Jolly 7; 14th Mar 2018 at 10:39 pm. Reason: Typo
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Old 14th Mar 2018, 10:46 pm   #2
ronbryan
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Default Re: Keeping tuning cord attached to spring

I tend to use small bits of tape to keep drive cords on pulleys and springs on tuning drums, but no doubt there are other ways. They are easy to remove when the job is completed.

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Old 15th Mar 2018, 9:26 am   #3
crackle
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Default Re: Keeping tuning cord attached to spring

What are you using for the replacement cord, some cords such as mono-filament fishing line are useless for this task. Even some of the braided fishing lines are no good because they are in essence flat and if used the cord will ride over its self.
I use waxed "whipping twine", available in various colours and thickness's from chandlers, for restringing. But on some transistor radios I have found the original cord is often glass reinforced, and needs to be quite tight with no stretch.
If the correct cord is used then glue is not always needed but if the knot needs sealing then PVA glue or alternatively nail varnish which sets a bit quicker.

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Old 15th Mar 2018, 9:53 am   #4
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Default Re: Keeping tuning cord attached to spring

I haven't (thank goodness!) re-strung a drive cord for a while, but I'm sure that one of the 'Loctite' range of sealants is suitable for the job. Firms like RS, CPC, and others stock 'Loctite' products. B.T.W. I have some 'proper' drive cord somewhere, not sure how much, but if any is needed, PM me and I'll check my cord 'stock!'
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Old 15th Mar 2018, 1:41 pm   #5
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Default Re: Keeping tuning cord attached to spring

I had the challenge of re-stringing part of the dial cord on a previous Philips B3G63A Restoration Project - fiddly indeed and took several attempts.

Can't emphasise enough the advice above to use 'proper' drive cord which is still widely available.

As for termination I just created a loop on the end of the cord and slipped on a Silver Plated Copper Cable Crimp Sleeve some of which I had left over from another Project. These really hold tight when crimped in place - again widely available through eBay for example.
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Old 15th Mar 2018, 2:21 pm   #6
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Default Re: Keeping tuning cord attached to spring

I've used nail-varnish on tuning cord knots (and the ends of cableform lacing-cords) in the past. Cheap enough, if you buy discounted stuff whose colour is no longer on-trend. Nobody cares if the colour's fashionable or not when it's used inside a radio!
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Old 15th Mar 2018, 2:24 pm   #7
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Default Re: Keeping tuning cord attached to spring

Quote:
Cheap enough, if you buy discounted stuff whose colour is no longer on-trend
I have scrounged it from Superdrug, merrily asking for some stuff that is being thrown away.

There are special knots for monofillament line, any good fishing site will tell you how to do them (never fished in my life).
 
Old 15th Mar 2018, 6:18 pm   #8
crackle
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Default Re: Keeping tuning cord attached to spring

Its not the knots that are a problem, if as you say you use the correct one, it is the stretch and slip.

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Old 15th Mar 2018, 6:31 pm   #9
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Default Re: Keeping tuning cord attached to spring

A figure-of-eight knot will usually hold on most cords, even monofilament, but is bulky. It's about the only knot that doesn't weaken the cord.
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Old 15th Mar 2018, 9:01 pm   #10
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Default Re: Keeping tuning cord attached to spring

I use a blob of evo stick on the knots
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Old 15th Mar 2018, 9:56 pm   #11
Jolly 7
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Default Re: Keeping tuning cord attached to spring

Thanks to everyone for your valuable suggestions. I have been using proper vintage tuning cord but will try the XYLs Sally Hansen's nail varnish first , over a figure of eight knot ! hi
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Old 15th Mar 2018, 10:29 pm   #12
tealandsilver
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Default Re: Keeping tuning cord attached to spring

Try using a blood knot. They are very reliable and never slip if tied correctly. The ends of the cord can be trimmed to within 1mm of the knot. Finish off with superglue if you want a really neat finish. I use them all the time. Note that if you use them with monofilament, wet the knot (saliva) before tightening to assist the turns closing up evenly.
http://www.animatedknots.com/bloodknot/index.php

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Old 15th Mar 2018, 10:37 pm   #13
Jolly 7
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Default Re: Keeping tuning cord attached to spring

Great stuff David. Thanks for the demo video link. Wetting the cord does make sense. It's similar to a tip I read many years ago; wet your shoelaces before tying them and they won't come undone easily.

Last edited by Jolly 7; 15th Mar 2018 at 10:38 pm. Reason: Emoticon error.
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Old 16th Mar 2018, 8:38 am   #14
crackle
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Default Re: Keeping tuning cord attached to spring

The problem with knotting dial cord is it often has to be done under tension. So I tend to always use a round turn and half hitches, then seal with glue or varnish.
Its the only knot I learned from my sailing days that can be tied and untied under tension, very important when mooring temporarily alongside.
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Old 16th Mar 2018, 8:47 am   #15
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Default Re: Keeping tuning cord attached to spring

There was a completely different method done in early transistor radios that used dial cords, especially near the areas where the dial cord attached to the spring.

A very tiny aluminium or brass ferrule was used, only with an internal diameter just big enough to initially pass two diameters of the cord, (the cord itself often less than 0.6mm diameter). Then after the cord was looped around through the spring end and then threaded through the ferrule, so that two cords passed through the ferrule, the ferrule was crushed with pliers to lock both the cords. No adhesive required and it didn't create a bulky knot either. It is in fact a very miniature version of the types of ferrules used in the marine & sailing industry on sail boats with ropes.
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Old 16th Mar 2018, 10:17 am   #16
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Default Re: Keeping tuning cord attached to spring

Yes I've seen the 'ferrule' method used quite a bit, and have used it myself: the little brass 'bootlace' ferrules designed for use with braided tinsel-cable (as found on things like phone handset-cords/two-way-radio microphones) work just fine in this application.
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Old 16th Mar 2018, 10:51 am   #17
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Default Re: Keeping tuning cord attached to spring

I seem to recall when using the nylon proper drive cord, a touch on the knot with a hot soldering iron produced a melt which seals the knot. No glue required.
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Old 18th Mar 2018, 6:07 pm   #18
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Default Re: Keeping tuning cord attached to spring

Would a drop of superglue work?
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