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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 15th Dec 2019, 1:57 pm   #1
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Join Date: Oct 2009
Location: Bergen, North Holland, The Netherlands
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Default Magic Stick

For the alignment of coil L3 in the Barlow Wadley XCR-30 I had to compress and expand the windings.
To be sure not to overdo things some kind of tool should be a help .
The recollection of an article in the book Elements of Radio Servicing by Marcus and Levy (1955, page 437) gave me the idea to copy their example of a tuning stick.
Just a rod with a a brass and steel bolt at the ends and it worked remarkable well.
But I am still a little surprised that differences in two metals would give such a reaction to an electrical field.
Jard N.
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Old 15th Dec 2019, 2:06 pm   #2
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Default Re: Magic Stick

The brass end acts like a shorted turn partially coupled to the coil of interest, reducing its inductance. The steel adds a ferromagnetic effect, increasing L but also increasing losses. A bit of dust-iron core is a better choice than steel.

Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
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Old 15th Dec 2019, 3:45 pm   #3
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Default Re: Magic Stick

And I suspect that a slug of aluminium (or copper or silver) might also be better than brass!
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Old 15th Dec 2019, 5:38 pm   #4
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Default Re: Magic Stick

Those were always known as "tuning wands" in my day. Brass one end {to act as a shorted turn and lower the inductance), ferrite the other end (to increase the inductance).

You don't need much of either to get a noticeable effect!

Reminds me of another 'tweak' I came across some years back - to increase the inductance of a coil, wind a bit of recording-tape round it! This has more than once been used here to add a smidgin of needed extra ""L" to bring to resonance an IF coil whose slug has been cracked/wedged by the Phantom Twiddler.
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Old 20th Dec 2019, 10:03 pm   #5
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Location: Hexham, Northumberland, UK.
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Default Re: Magic Stick

I made a tuning wand many years ago but the only time it moves is when I rediscover it every once in a while among my other "tuning sticks" of various vintage. I was convinced when I originally made it that it would be in constant use but sadly no. The wand is made from an RS cotton bud stick, with a hollow ferrite tuning slug jammed on one end and a small brass stand off pillar jammed on the other. It does work well though, should I need it one day.
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