[HBR] Coils

[Walt Hutchens]

Darrell wondered:
> Does anyone have a better method than using strips of Duco cement for
> attaching coil windings to polystyrene coil forms?

I agree with the comments that Duco's not good.  The original product 
was cellulose acetate with a solvent appropriate to that.  It didn't 
work well on polystyrene.

There was a special glue consisting of polystyrene in a solvent that was 
effective.  Is Q-Dope what I'm thinking of?   Clear Krylon plastic spray 
is a dilute version of the same thing, though you'd have to be careful 
to get the right item as Krylon has been 'shelf-spaced' like everything 
else -- that is, one product has become three or more as manufacturers 
discovered that the more shelf space their stuff occupied, the more they 
sold.

With product using a proper solvent you get a different problem: They 
work well because the solvent does dissolve the base material, so you 
get a real bond.  BUT in doing so, the solvent causes the base to expand 
slightly, which can easily lead to cracking or crazing.  I think either 
the Q-Dope or Krylon would be worth trying, but I would test first on a 
scrap piece.

Krylon also makes a line of spray can paints that bond to plastics. 
Those are somewhat different, I believe, and since they're intended for 
use on plastic might not cause the cracking/crazing problem.

The clear polystyrene-in-solvent products will have NO effect on Q. 
They are complete non-conductors, and were often used in high voltage 
applications.  With the paints the issue would be the pigment; my guess 
would be that they'd be okay too but some study of labels and possibly 
experimentation would be a good idea.

Use of a complete covering (Krylon ...) will increase the distributed 
capacitance of the coil significantly but probably not enough to take it 
out of the range of the trimmer.

Walt Hutchens
KJ4KV