Re: Problems with primary arc gap scopings.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Harvey,

At 02:54 PM 3/14/2002 -0800, you wrote:
>I have set up a conventional tesla primary tank
>circuit with the arc shunting the L and C quantities
>in series.  I have done this to compare the actions of
>a Marx voltage doubling arc gap that uses oppositely
>phased L and C quantities in series,(4 L and C values
>instead of 2) with the arc gap made at each midpoint
>of each phasing in parallel. The operation of this gap
>seems much smoother that the staccato like operation
>of a conventional arc gap, and fires at much smaller
>input voltages than the equivalent conventional arc
>gap. 
>
>However to employ such a scheme for an actual tesla
>coil construction, a certain problem becomes in
>predicting what the resonant frequency of this primary
>arc gap using 4 components will be. My thinking is to
>use 2L or above to account for any mutual inductance
>between dual primaries, and then to use C/2 as the
>capacity, thus to derive the possible resonant
>frequency 2L and C/2 should be used as the respective
>inductive and capacitive values.
>
>It was then thought that placing a scoped inductor
>around the vicinity of the firing gap should show the
>predicted frequency. However all of these scoping
>methods seemed to show a much higher frequency of
>operation than is being predicted.
>
>This is the reason I reassembled these L and C
>components back to a conventional tank circuit and
>then employed the same method of inductive scope
>sensoring. However I am still getting about 10 times
>higher frequency than should be predicted.

I don't see how you have all this connected (I am sort of a
schematic/picture kind of guy :-))  However, if you have two coils
magnetically coupled to each other, the inductance either goes up 4X (n^2)
or goes way down.  If the currents add, then you get far greater
inductance.  However, if one of the coil's currents is in the opposite
direction, the magnetic fields cancel out and the total inductance is very
small.  Only the connecting leads have inductance then.  If you are getting
such a very high frequency, this may be what's is happening.  Even though
you have two big coils, the inductance may be very near zero depending on
how they are connected.

>
>I have seen others use a capacitive plate sensor
>method, and wish to try this to see if the inductor
>itself is causing a possible error in measurement. Can
>anyone comment whether the inductive sensoring method
>is a bad choice for scoping a tank arc gap? I also
>need suggestions for dimensions of these test
>capacitor plates. I was thinking of using a long
>cardboard box with aluminum foil taped to sides
>separated by about 3 inches. I also have a very large
>4.2 nf air capacity obtained from a electrostatic air
>cleaner, would this be a bettter capacitive sensor, or
>is the conventional dual plate (small capacity sensor)
>preferable?

See:

http://hot-streamer-dot-com/TeslaCoils/MyPapers/planant/waveant3.html

You can easily make it quickly out of aluminum foil and other "easy" stuff.
 No dimensions are critical.  It can easily pick up fields off the bare
primary circuit.

>
>Thanks for any help, and also thanks for the great
>info given by Terry on digital scopes on the test
>instrument thread.

:-))

Cheers,

	Terry


>
>Sincerely Harvey D Norris
>
>
>