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Re: Tesla!

Re: neon sign transformers...I should have a chance to try shorting 
the output terminals this weekend, and I'll let you know what I find.  I 
thought that the current from a neon sign transformer dropped almost to 
0 (zero) when it was actually operating, and that the full voltage and 
current was only available before the neon started conducting.  Once 
the sign is lit, it takes only a fraction of the current and voltage to keep 
it going.  You can get high power-factor neon sign transformers,  
whatever they are, that might behave differently?

According to the Bylund "book", to demonstrate the current limiting 
action of a neon sign transformer,  you can put two oppositely biased 
LED's directly across the secondary terminals and they will light up 
normally, not explode or burst into flames.

The next part is from a newsletter I received about 10 years ago.  I've 
never tried it, but I'm going to use it when I make my next primary.

Castable insulating compound (courtesy of Peter Lefferts, 1985)

Materials:
==========
- Paraffin wax
- Shredded soft polyethylene plastic (translucent coffee can lids, etc..., 
  avoid plastics that are stiffer or make a white line when creased)
- Salt
- Two large stainless steel or glass-porcelain covered pots 
    (one of which will sit easily inside the other)

Preparation:
============
Make a high temperature double boiler where the inner pot sits in the
water, not on the bottom of the outside pot (supports might be
necessary for the inner pot).  Put enough wax in the inner pot for
your purpose.  The inner pot will need to be weighted because the
outer pot should have enough water to come to about an inch above the 
melted wax level.  Boil the water in the outer pot while adding salt 
until no more will dissolve.  This raises the boiling point for a 
better product.

Compunding:
===========
When the wax is melted, start adding the slivers of polyethylene.
Stir every few minutes to prevent the poly from sticking to the
bottom and browning.  When about 1/2 of the poly appears melted, add
more.  Add water to the outer pot to keep the level one inch higher 
than the compound level in the inner pot.  As soon as a hint of 
cloudyness appears in the mixture, or the consistency of thin oil 
appears, stop adding poly, and heat and stir a little longer.

Casting:
========
A mold of good dense cardboard, glued watertight sides and bottom
with ample epoxy should be prepared well ahead of time.  Seal any 
wire joints likewise.  Do not use other plastics such as acrylics 
as molds. Practically all epoxies and hard magnet wire insulations
will stand up to the heat and solvent characteristics of this
compound. Pre-heat the mold cavity, using an oven for small objects
or a hair drier for larger ones.  If using an oven, pre-heat it to
250 degrees before putting the object in.

If a primary is being molded, be sure that several taps for tuning 
are brought out through the mold.  Also if you want to take the 
cardboard off later, smear the inside with silicone grease. 

Pour rapidly but without splashing (HOT!). Shake gently to bring up 
bubbles.  If a small leak appears, patch with tape and blow with a
hair drier on cold until the plastic in the leak is well solidified.


Steven Roys (sroys-at-radiology.ab.umd.edu)