Message-ID: <A0D4F51D1CA8476783D3C2E557DD8178@DELL4>
From: <jrusgrove@comcast.net>
To: <rsgb_lf_group@blacksheep.org>
References: <16856e12994.marcocadeddu@tin.it> <92fbbb62-a1fe-0e0f-c048-08dd3c2cdfb2@n1bug.com> <1973353494.20190117121430@gmail.com> <c634d312-92d3-faac-d48e-433e1ab12fda@n1bug.com>
Date: Thu, 17 Jan 2019 09:56:31 -0500
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Subject: Re: R: RE: LF: JT9-10 vs JT9-5 test ends with smoke :)
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Just double nut on each side of the plastic ... 

Jay W1VD


----- Original Message ----- 
From: "N1BUG" <paul@n1bug.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, January 17, 2019 7:34 AM
Subject: Re: R: RE: LF: JT9-10 vs JT9-5 test ends with smoke :)


> Hi Chris,
> 
> That is an interesting idea. I think it should be a press fit to so
> it doesn't tilt to the side and cause the coil winding to be a bit
> loose.
> 
> I was thinking along another line. Use a machine screw through the
> coil form as before (make it brass this time), but instead of
> attaching the inside were lug under the screw head, bring the wire
> out through a hole near the machine screw, bend it over and put a
> lug on it outside. Then this lug and the one from the end of the
> coil itself can be pressed against each other between two nuts (or
> nut, lug, lug, lock washer, nut). The would assure better contact
> and should reduce the tendency for the most critical part of the
> assembly to loosen. If one were to be very paranoid, he could even
> solder a short safety jumper from lug to lug. ;-)
> 
> 73,
> Paul
> 
> 
> On 1/17/19 7:14 AM, Chris Wilson wrote:
>> 
>> 
>> Hello N1BUG,
>> 
>> Personally I would machine or cut a piece of brass tube so the bolt
>> head, nut and washers, plus the connectors are tightened against the
>> brass tube, not the plastic. The tube can then just be a loose or push
>> fit into the plastic former.
>> 
>> Thursday, January 17, 2019, 12:01:19 PM, you wrote:
>> 
>>> Hi Marco,
>> 
>>> It's always interesting to see pics from other collections if you
>>> want to share. :-)
>> 
>>> After careful study of the ruined coil, I made a guess:
>> 
>>> SS hardware was a poor choice. Using the machine screw to carry RF
>>> from inside to outside of the coil form was not the best way. I
>>> think the hardware became slightly loose. We have all seen this
>>> happen when hardware is installed in "soft" plastics. Loose hardware
>>> caused higher resistance in the connection and more heat. More heat
>>> softened the plastic, which made the hardware more loose, more
>>> resistance, more heat. Eventually the connection became so loose
>>> there was an arc, too much heat and everything burned.
>> 
>>> Well, it's just a guess, but it's not too hard to imagine this can
>>> happen.
>> 
>>> Every nut and screw on that unit was a bit loose, even the ones that
>>> did not yet show any sign of overheating.
>> 
>>> I cut and drilled already a new coil form but I wait now for brass
>>> hardware to arrive before winding.
>> 
>>> 73,
>>> Paul
>