Most people believe spark gap Tesla Coils can only be operated from high voltages - typically 4 - 15kV or more...  But some unusual experiments can be made with as little as 240V - directly.

(http://www.electrotherapymuseum.com/2009/15Nov09/DSC08664.JPG)

Outside of very low frequency Pancake Coils, there is little practical applications for using such low voltages.  But it is interesting that the concept works.  Tesla did state that he operated spark gaps with low voltages, and this is proof.  The setup is particularly useful though for induction coils and kindred apparatus...the effects seem to mimick those of electrolytic or mercury interrupters to some extent.

I've made a few experimental coils using scrapped transformer windings, old radio inductance coils, and even a single layer secondary reminiscent of a normal Tesla secondary coil...

(http://www.electrotherapymuseum.com/2009/NewInductionCoil/DSC08709.JPG)
(http://www.electrotherapymuseum.com/2009/NewInductionCoil/DSC08710.JPG)

(http://www.electrotherapymuseum.com/2009/16Nov09/DSC08694.JPG)
(http://www.electrotherapymuseum.com/2009/16Nov09/DSC08690.JPG)

In these examples I'm using a 120 - 240V transformer, actually a small mercury vapour lamp ballast.  To limit the current I have a small electromagnet as a choke coil.  For the capacitor I have a bunch of old microwave oven caps rated at about 2kV 1 mfd.  I also have a 7.5 mfd motor run cap rated for around 300V.  In the initial tests I was using between 7 and 9 mfd.  The spark gap is a micrometer gap from a Bovie surgical Tesla Coil.  It is adjustable in small increments, and can be easily set to 1/1000" or less.  The contacts are 5/16" tungsten.

Induction Coils and even some Tesla Coils can be used with this circuit to power external apparatus -
(http://www.electrotherapymuseum.com/2009/16Nov09/DSC08686.JPG)

Unusual Tesla Coil circuit powering an additional Tesla Coil...

Here is the unusual schematic:
(http://www.electrotherapymuseum.com/2009/16Nov09/DSC08698.JPG)

And some sample sparks from the Tesla Coil powered by this:
(http://www.electrotherapymuseum.com/2009/16Nov09/DSC08689.JPG)

More pictures and experiments are here:
http://www.electrotherapymuseum.com/WhatsNew2009E.htm (http://www.electrotherapymuseum.com/WhatsNew2009E.htm)


I'm sure there are better ways of doing this with solid state, but for something unusually simple, it makes a curious experiment...

Jeff Behary

Here is the latest incarnation of this concept, with a movie:
http://www.electrotherapymuseum.com/2009/InductionApparatus/index.htm (http://www.electrotherapymuseum.com/2009/InductionApparatus/index.htm)

Output is 4", from a flame to a crackle depending on the choke coil sizes...

(http://www.electrotherapymuseum.com/2009/InductionApparatus/DSC08788B_thumb.jpg)

Will try to rectify the 240VAC tommorrow to DC to see the effects...

Jeff

Soon you'll have it "singing" to music:

http://www.youtube.com/user/rscopper6#p/u/13/DvQy9VY0s3w (http://www.youtube.com/user/rscopper6#p/u/13/DvQy9VY0s3w)

Capper