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Richard Knoppow · December 7th 06, 03:11 AM posted to rec.radio.amateur.homebrew

"Chris Jones" wrote in message
...
wrote:

All,

I've been hearing how winding coils on discarded plastic
pill bottles
is not suitable for RF tank circuits due to low Q, and
that these would
not be safe for tube circuits anyway due to melting
point.

I have access to kaolinite clay (white porcelain) and a
kiln, and I was
wondering if I molded and fired this type of clay for
coil forms, what
effect on a tank circuit Q this form would have.

Thanks in advance,

The Eternal Squire

Although the frequency is probably not the same as what
you're going to use
the coils for, one way to test the loss of an insulator
material is to put
some in the microwave oven (along with a mug of water to
provide a load for
the magnetron). If the insulator material gets hot, then
it is lossy. Of
course you would have to fire the clay before testing it,
otherwise the
water content would make it get hot anyway.

If the pill bottles are polypropylene or a similar
non-polar plastic then
they are probably not very lossy, but of course if the
current through the
wire makes the wire hot by normal I^2*R losses, then the
hot wire would
melt the plastic. This would only be a concern in a power
amplifier or
tube circuits as you mentioned.

Chris

FWIW, I looked at a number of old pill bottles out of
curiousity, they are all marked PP No.5 which is
Polypropylene. Checking in a microwave oven sounds like a
good idea.

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Richard Knoppow
Los Angeles, CA, USA