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RE: Brass Ball static spark gap not doing so well

Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pkomen-at-zianet-dot-com>


I was setting the safety gap with it connected in the protection circuit and
thus to the NST.  I set the static gap with it connected to the NST only.  I
tried a different approach today and set the safety gap, then connected the
static gap in parallel (the usual place, across HV after the protection
circuit with safety gap.).  The gap is now 25 gaps of 0.005" (set with a
feeler gauge; 0.005 was go, 0.007 no go).  When the static gap fired, the
safety gap also fired.  From about 0.161" (again checked with a feeler
gauge) per side, I opened the gap to 0.199".  Now the static gap arcs but
the safety doesn't.  I'll try it with the TC as soon as I can.

I am wondering about building a version of your static gap (multiple pipes
and all).  See below.


I will probably try a single sucker gap sometime soon.  I have an old vacuum
cleaner that I could use.  If it's low maintenance, low resistance, why not?


I'm beginning to think that copper is the way to go.  The problem I see with
balls is that the arc jumps the gap in only one place.  With the multiple
pipe Terry gap, the arc can jump anywhere on a 2" section of pipe.  The ball
concentrates erosion in one place.  So far with brass, the performance
degrades so fast that it is hard to tell if tuning changes make any
difference; i.e., move the primary tap in and streamers shorten, move it
back out and they are still shorter.

Anyhow, thanks for all the replies.  I imagine that I will build both a
sucker gap and a Terry gap, because I enjoy building stuff, and I'd like to



-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, May 26, 2001 11:30 AM
To: tesla-at-pupman-dot-com
Subject: Re: Brass Ball static spark gap not doing so well

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

Hi Pete,

You can set a regular gap's firing voltage the same way you do a safety
gap's voltage.  With 'only' the NST connected.  At full input voltage, the
NST output voltage will be at the transformer's rating.  You set the safety
gap to just not fire but you can also set a regular gap to be sure to fire
at this voltage.  With a variac, you can even input a variety of voltages
and perhaps determine a number of gap settings.

A lot of things affect the actual voltage so it is best to test it like
above.  A 15/60 NST has a peak output voltage of 21000 volts so a safety
gap set at 25kV and a regular gap set at say 20 kV would be good.  Static
gaps firing voltage does change with use (seems to go down).  They do tend
to "break in" and become more stable after awhile.  There are all kinds of
variables depending on power, shape, materials, etc...



At 12:23 AM 5/26/2001 -0600, you wrote:
>Second light on my coil.
>Arcs not as long as they should be.  I think that the toroid is too rough;
>20 inches across with 4" minor diameter.  Made of dryer duct not fully
>covered with aluminum tape.  Gives a number of streamers from the same 8 or
>10 points.
>I have a new spark gap made of 15 - 1 1/8" brass balls spaced 0.022" apart.
>Air is blown around them but not specifically at the gaps.  Things started
>out OK, but the arcs kept getting shorted over a period of 10-15 minutes.
>am running a 12kv, 60ma NST with protection circuit and 4 strings of 11 of
>the Panasonic caps for about 20nf.  The NST alone will jump 11 of these
>gaps.  When running in the TC, only 7 or 8 could be used without the safety
>gap firing.  Safety gap needs cleaning and a reset.
>When I quit tonight and dismantled the spark gap, the brass balls had a
>circle of black crust with a larger circle of tan around each sparking
>point.  There are pits in the brass itself (it looks like tiny balls
>together with the areas between eaten away).  It seemed that the break rate
>had gone way up, almost to the point of power arcing.
>Question for Terry referring to your Terry gap at:
>It states that you use about 600v per 0.004 inch gap (60 pipe sections for
>maximum of 58 gaps).  I am using a multiple section gap now.  My 12kv NST
>jumps 7 gaps of 0.022 inch (as close to that as I can set them).  If I
>a similar spark gap to yours, should I expect to use 28 gaps (12kv * 1.4 /
>600v per gap) or 38 gaps ( 7 * 0.022 / 0.004)?  If it will only jump 28,
>use 60 sections of pipe or would a smaller gap be better? 0.002 inch maybe?
>More general questions:
>Does the optimum setting for a static spark gap, whether number of gaps or
>size of the gap(s), depend on the atmospheric conditions (humidity,
>pressure, etc.)?  My location, Las Cruces, is about 4000' altitude and very
>dry (desert).  Humidity of 50% is very high and very rare so I suspect that
>I could set a spark gap and forget it.  Would a Florida coiler (I lived in
>Palm Bay for a few years where the summertime humidity got as low as 78%,
>elev. about 20 feet) have to set the gap wider?
>As the number of gaps goes up, does the total gap go down?
>I looked at the Tesla Mailing List archives for spark gaps and somebody did
>an experiment that indicated that the single spark gap has a more
>firing voltage.  Someone else reports longer arcs with multiple unequal
>gaps.  Someone else reports longer arcs with aluminum electrodes between
>copper ones.  I am beginning to wonder what we really know about spark
>I know very little.
>Is a multiple small gaps spark gap better than a single gap?  Which has
>greater losses?  Which has the most consistent firing voltage?  Is there a
>spark gap that lasts longer between cleanings?  Is there an optimum static
>spark gap?
>I hope that I am not bringing up something covered already.