Norm, and anyone else interested:

Norm, you wanted to know if your 25kV DC capacitor would be okay:

Well, I can't really speak for the DC problem, but I would like to let
you in on a private little secret amongst us coilers:

Even though your power supply may only be 10kV, the voltages across the
capacitor may reach as much as 3 times that value, or more, on a 60Hz
Line.  Here's why:


The secret:
	Well, I'm not positive about all this, but I think this is the way it
works:  The current through a capacitor is equal to the capacitance time
the rate at which the voltage across it drops (or rises, whatever).  Now
just because the max voltage produced by your power source is only 10kV
(or 15kV, whatever), that doesn't mean that the value of capacitance
times voltage change won't be huge.  Also remember that the voltage
across a capacitor is its reactance times current.  
	This means that at any particular time, huge Capacitive Reactance times
huge current (current is huge because of reasons stated above) = huge
voltage across your capacitor (possibly much larger than whatever your
power supply is).  Most of the experinced guys I have worked with say you
should use a capacitor rated for at least 3 times the voltage of your
power supply.  

> . . . I have seen pictures of the primary coil wound  vertical, 
>horizontal  and conical...what are the differences in results . . .

	Well, first I want you to know another secret that most otherwise well
informed people don't know:  You don't necessarily want a tight magnetic
field coupling between your primary and secondary coils.  These different
coil forms offer different degrees of loose coupling.  You'll have to
wait for an answer from the really experienced guys like FutureT, and Dr.
Resonance, and those guys, to tell you exactly which one is best.  The
differences are that the vertical primary coil is probably the easiest to
build.  The flat spiral and conical give a little looser coupling, and
are generally better.  

	I suppose the flat pancake spiral is a little easier to build that the
conical.  Most of the best coils I see are built with flat spirals,
though.  But like I said, you have to wait for one of these big dogs to
tell you exactly when and where a conical beats a spiral and vice versa.

>3. I have a small dc motor that I can control the speed ....I am 
>of using it to power a Rotary spark gap.  Cant I tune the primary by 
>changing the speed of the motor??

	Well, again a big dog on this list might disagree with me, and if they
do, then believe THEM.  But anyway, I don't know of any way to tune a
coil other than to change the inductance of the primary, or change the
capacitance of the tank circuit.  

	Now, once the circuit is in tune, yeah, there might be an optimum motor
speed so that the spokes of the rotor line up at some angle every time
there is a pulse from the tank capacitor.  But really, I think that's the
idea of a Synchronous Rotary Spark Gap, which is another topic you might
want to ask the list about.

							Safe Coiling:


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