IF and RF adjustment Coils

[percival007]

Good morning all,

I hope this is in the right place.

I am replacing the thin length of 'elastic' (?) thread which is inside the IF and RF adjustment Coils in most Radios but in this case a Troughline II
The original has perished and so the Ferrite inners are loose and prone to drifting.
After asking on here what it was called (!) I have found some, actually quite a while ago but am just getting around to fitting it.

My question is when fitting the new thread, is it best to pull it a little taught or leave it slack as the Ferrite inner is inserted?

Also, are replacement Ferrite inners available anywhere? Some in the LEAK were damaged and although I have replacements from donor Troughlines that would mean those sets become un-resurrectable.

Many thanks,

James.

[Radio Wrangler]

Rubber thread.

You used to be able to get something like it by unravelling a golf-ball or knicker elastic.

It is unlikely that the cores are actually Ferrite. They are usually dust-iron, sometimes called carbonyl iron. It's much crumblier than ferrite. The permeability is lower, but its losses at high frequencies are lower and its temperature coefficient is better, too.

I think Neosid were the main supplier of such cores in the UK around the time of those tuners. First step is to find the diameter and pitch of the threads.

David

[Ted Kendall]

They still list over twenty varieties of slug on their website. Whether they would supply in penny pieces is another question.

[Wendymott]

Knicker elastic.. Sharp knife... separate the individual strands....then untwist the cotton double layer ..Ideal for Toko formers.

[Leon Crampin]

PTFE tape works far better. It's low loss, and you can adjust the stiffness of the locking function by means of the amount of tape you use.

Leon.

[regenfreak]

Originally Posted by Wendymott

Knicker elastic.. Sharp knife... separate the individual strands....then untwist the cotton double layer ..Ideal for Toko formers.

I have used cotton strands, wax paper and Flexoid (not recommended as it stinks). I have not tried Knicker elastic, let me look at my drawer

[regenfreak]

Originally Posted by Leon Crampin

PTFE tape works far better. It's low loss, and you can adjust the stiffness of the locking function by means of the amount of tape you use.

Leon.

thanks. Will try it

[Ed_Dinning]

Hi Gents, later units often used Kilopoise, an extreme viscosity lubricant that is still available in various grades of "stickiness"

[Radio Wrangler]

I have a jar of Rocol Kilopoise that I used to use on tuning slugs. Affectionately known around the plant as 'slug slime'

It's the stuff that's used on camera lens focus helices to give them that ultra smooth feel, usually a bit less viscous grade than slug holding grades.

It's the price nowadays that's shocking.

David

[Leon Crampin]

In valve equipment which runs hot, the Rocol compound doesn't age well, usually ending up too stiff to allow core readjustment without damage. PTFE is inert.

Leon.

[regenfreak]

Originally Posted by Ed_Dinning

Hi Gents, later units often used Kilopoise, an extreme viscosity lubricant that is still available in various grades of "stickiness"

ED there is a 3kg can of Rocol KILOPOISE High Viscosity Damping Grease at £388 plus £40 shipping on ebay now.

Two rolls of PTPE is £1.5 free shipping.

[Radio Wrangler]

There's been an outbreak of slow motion mechanisms from kitchen cabinet door closers to bog seats. Even the grab handles over the passenger seats in my care are slow-return. There must be damping grease in these things, but I don't see the manufacturers paying the price of kilopoise.

David

[percival007]

Thanks for all the suggestions as to what to use, although I have got what I think is the right material.

However no-one has suggested the technique for its correct implementation.
My question was that, is it best to stretch it slightly whilst inserting the ''carbonyl iron'' ''slugs'' or leave it slack?

Cheers,

James.

[Radio Wrangler]

It would have been too fiddly to have had to stretch it in a production environment, but then they would have had exactly the right size of rubber the fit was designed for.

Being able to do some stretching gives you a bit of 'wiggle room' to be able to use whatever thickness of rubber thread is available to you. So you're just going to have to decide based on what it feels like. Just don't get it too tight that the core breaks up.

I know, that's as good as the old advice 'Tighten to 22.5 degrees before the point at which it shears off'

David

[turretslug]

Originally Posted by percival007

Also, are replacement Ferrite inners available anywhere? Some in the LEAK were damaged and although I have replacements from donor Troughlines that would mean those sets become un-resurrectable.

Good ol' J. Birkett of Lincoln were listing a couple of sizes of slugs (I always thought they looked more like ladybird larvae myself....) for standard British coil formers and may have others- I can't remember size or grade but I don't suppose Leak would have used anything bespoke or exotic. Unfortunately, they stopped listing in Practical Wireless a while back, nor do they show stock on the 'net but they do have an electric telephone- 01522 520767.

Good luck with it, I think these are a lovely classic design,

Colin