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Re: Just a FEW questions from a newbie



At 10:59 PM 1/8/97 -0700, pdalinis-at-xnet-dot-com wrote:

>One question that I cant figure out is how do you create the frequency
>to emit the magnetic
>fields?  Using a ignition coil switched with a 555 timer circuit would
>do it.  I understand that.
>But with just a spark gap?  How do you adjust the frequency to meet the
>1/4wave on the
>secondary?

It does sound confusing, but it's rather simple. The resonant frequency is
determined by the size of the primary capacitor and the inductance of the
Primary coil (a series LC circuit) When the system is tuned right, the
capacitor reaches it's maximum potential charge at just the right instant.
When this happens, the spark gap fires and acts as a "high-voltage switch"
and transfers all the power from the capacitor through the primary. Note
that this power can be thousands of volts at hundreds of amps. it is LETHAL.
>For my first coil, I am looking for a design that gives off 1 foot
>sparks.  If I get more, that 
>is fine too :) What secondary size am I looking at?  2feet long by
>3inches dia?
For 1 foot sparks, You could use a 15KV, 30 or 60 ma Neon transformer.
These are cheap and readily available. Just call or go to any local sign
shop that deals in Neon signage and ask them what they do with their old,
out-of-warranty neon sign transformers. Some places just throw them out
because they can't sell them without providing a warranty of some kind..;)
However, most places that I have called usually keep the old ones in a box
in the back room and save them for teachers, instructors, COILERS, anybody
who wants them. They usually let them go for a small fee ($10-$25).
On the size: The best height-to-diameter (h-d) ratio for coils under 8" in
diameter is around 4:1. So, if you're making a 3" dia coil, it would be
best to use a height of 12".
>I have access to the following transformers:
>24VDC in - 6KVDC out
>24VDC in - 10.6KVDC out
>
>Unfortunatally, I dont remember the current rating.. I do know they are
>in milliamps.
Well, what's going to make the difference in this situation is the current.
Minimum, I'd suggest 60ma and 30ma, respectively.

>What they are and where they came from is a mystery.  Another solution
>that I can
>think of using would be a ignition coil off a car which would be:
>
>12VDC in - ?????VDC out  (I would have to use a 555 timer circuit to use
>this one,
>right?)
> 
>Which one would be the better one to use?

Unfortunately, when you use a Ignition coil there isn't much current
available. Therefore, you won't get very big sparks at all.

>Capacitors.  Will doornob caps work a-ok?  Perhaps a few in series and
>parrallel?  
>Where can I go about getting some?  (no worthwhile hamfests in winter in
>chicago)

There is a great surplus company called "All electronics". They
occasionally get some high-voltage products in for pretty good prices.
Example: in their summer '96 catalog (the last one i got...they're not very
good at sending out the latest ones...;) they have HV Mica caps from 600V
to 2,000V in 3 different styles in values from .0003 to .02 MFD for 25
cents each! Their # is 1-800-826-5432.

>Spark Gaps.  I found some docs for a rotary one, and a stationary one. 
>The stationary
>one looks easier for me to build is it ideal (airblast.txt)?  Will an
>aquarium pump work for 
>the air?  How about an airbrush compressor?  

I have that very same text file. It came with a .GIF that illustrated how
it was built. That may work fine for you, however it is very noisy and the
electrodes don't last long. Unfortunately, neither an aquarium pump or a
airbrush compressor provide enough airflow to effectively "quench" the
spark. The result is the gap electrode life is dramatically shortened. The
best design I've seen for a stationary spark gap is one designed by Richard
Quick. It's affectionately referred to as the Richard Quick spark gap (go
fig). I can send you construction details if you're interested.

>Tank Curcuit.  I have seen many different configurations for this. 
>Which one will
>work best for my setup? 

To my understanding, the best tank circuit is having the primary capacitor
in series with the input transformer and having the spark gap in parallel.

>Static Gaps.  I have been reading, and it appears that some of you have
>more than
>1 gap in your circuit.  Why?  Will I need more than 1?  Are these
>fixed?  

The idea behind having more then 1 spark gap (Series stationary) is it is
quieter, runs cooler, and has faster "quench times". This causes the
electrodes to last longer.

>Primary winding.  Why is this tapped?  Is this how you tune it?  What
>medium do
>you suggest I use for this?  Common sense tells me to make this coil
>larger
>than what some docs say.  5 turns of wire taped at 3 seems WAY to small
>to me.
>50 turns tapped at say 35 sounds more efficient to me... but that is me
You are correct in the fact that the tap is to tune it. The best material
for primaries that I have seen is 1/4" to 3/8" flexible copper
refrigeration tubing. Since at the frequencies that the tesla coil uses are
anywhere from 100Khz to 1MHz, the current causes a "Skin effect". What that
means is that the current only penetrates the conductor a few mils, and
travels on the outside od the conductor, as opposed to traveling through
it. That is why you can use realitively thin-wall tubing.

>I have access to the following magnetic wire from Allied Electronics:
>
>Belden Heavy Armored Poly Thermaleze high temp wire 22awg Belden8077 
>501ft $29.38
>Belden Single Beldsol Solderable magnet wire  22awg Belden8051 254ft
>$17.34
>
>Dearborn Single Polyurethane Class A Type T-1 105 degree C  22awg
>.0266"od $20.81/pnd
>Dearborn Heavy Poly-thermaleze Class F type T-2  155 degree C  22awg 
>.0277"od  21.83/pnd
>Dearborn Corona Resistant High Voltage Wire UL Style 3239 150 degree C 
>10kvdc-40kvdc $???
>
>Which one do you suggest I use?  22AWG the size to go with?

WHOA! Don't buy that wire! That is way too expensive! Go to your local
electric motor repair shop. They usually will sell you some wire for under
$5 a pound. The best gauges for wire are #26 and lower.

>How nessacary is the Choke circuits?  Is the feedback going to be that
>bad?  I dont
>see why it would if you get your SWR down enough.  

I'd help you with that one, but I'm a bit confused about that one myself...;)

>Sorry for all the questions.... but I dont know where else to go!

Not a prob, that's what we're here for!

James