Re: R: RE: LF: JT9-10 vs JT9-5 test ends with smoke :)

[N1BUG <paul@n1bug.com>]

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