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Re: Lowered Expectations

Jim,
  
You can build a Spark Gap Tesla Coil using 120 VAC.  It takes a little,
electrical, cheating . . .  120 volts won't jump enough of a gap to be
practical and you would still need current limiting, so you can use an
inductor to give an extra jolt (500+ volts).

I did some fooling with what the early literature calls a "Kicking
Coil."  (still in use today and sold for testing laboratory glassware
for pinhole leaks).  

Basically, you wind an iron core inductor.  The core is connected to a
set of contacts that will break the circuit as the core magnetizes. 
What you have at this point is an AC/DC buzzer . . .  The Tesla primary
is wired between one contact of the AC line and carries current to one
of contacts that breaks the circuit to the core.  (the other contact is
wired in series with the inductor)  The cap is across the contacts.

You can make a cheap and dirty version of this by using a relay and just
wiring the contacts so a normally closed contact is in series with the
relay's coil.  (but don't expect very hot sparks)

A better technique is to make adjustable contacts (ala model T spark
coil primary) and wind your own inductor or cut up a shaded pole
induction motor, transformer, etc. to make an inductor.

This will yield brush discharges from a point of about 3-4" long.

At the low end of things, you can also get an ordinary spark coil (20
VDC) to work.  I used a 555 astable to drive a darlington transistor
that drove the coil as a pulse transformer.  The spark was enough to
power a 1-1/2" diameter X 13" of 32 AWG wire.  I think the primary
capacitor (wired across the spark gap) was 500 pf / 12kv, and the coil
twenty turns of 14 AWG.

The relay interrupter can be adapted as well.  The buzzer has to have
normally open and normally closed contacts to work well.  The spark coil
is wired so that the normally open contact supplies power to the coil,
and gets a condenser similar to an auto's ignition system.  Dwell time
is set with an electrolytic cap across the relay's coil.  (another DC
low voltage circuit)  

I can try sending you a schematic as an attached file if you like.

Model T spark coils will work.  Gas stove, water heater, ignition
transformers will work (5 KV, 6 ma) in ordinary TC circuits, on a very
small scale.  The lower limit is probably around 10 watts input power.

My smallest coil is a 1" test tube wound with 34 AWG for six inches.  It
is a horizontal bipolar coil and can demonstrate some pretty (3-4")
discharges, with a flea power spark exciter.

I went small after wiping out some computer memory.  The stereo could
take a direct hit, not so a computer, it wants to be in another county,
when I fire the bigger coils.  I try to test theories on a small scale
then play with the >1KVA stuff, if it looks promising.  It seems to be a
good technique.  You really have to optimize everything to get a small
coil to work.

"High Frequency Apparatus" by Thomas Stanley Curtis, Published in 1916,
republished by Lindsay in 1988, has a number of interesting circuits as
well as a kicker.  

The "Amateur Scientist" article on X-rays has whole kicker coil tesla
setup to power the X-ray machine. The URL is  >  
http://www.noah-dot-org/science/x-ray/index.html  It is a slow site, you
want figure 231 for the schematic, if you operate the browser sans
pictures, 232 is a pictorial drawing.

good luck
take care
bob

Tesla List wrote:
> 
> Original Poster: "JimmyD" <jim_del-at-email.msn-dot-com>
> 
> Is there any reason one couldn' build a Spark Gap Tesla Coil setup using
> 120v line voltage?
> 
> 
> I know everybody's trying to have the biggest, but what are the limitations
> of going smaller?
> 
> << Jim >>