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[TCML] copper tube stationary gap - was: NST rebuild good

Hi Bart,

Thanks for the info. BTW, 1" copper pipe is the largest that
I can find in my local Home Depot or Lowe's. Did you have to go to an actual old-fashioned hardware store to find the
1 1/2" copper pipe? I know that larger diameter copper pipe
can be obtained at a plumbinng supply but you mentioned getting yours at a hardware store. I still have about a 6 ft. length of 1" copper pipe and I hate the idea of having to buy more larger idameter copper pipe at its current price$.
(A 10 ft . length of the 1" stuff at my local Lowe's is now
Also, what size of toroid would you recommend for my pro-
posed coil? I was thinking around 6 x 24 or possibly even
8 x 30 (inches). Looks like it's getting close to time to get
another TCML toroid bulk buy ;^)


----- Original Message ----- From: "bartb" <bartb@xxxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Friday, January 11, 2008 4:08 PM
Subject: Re: Re[TCML] NST rebuild good

Hi David,

Your undersized in caps for SRSG LTR operation (you would need 4 of those caps). But they are large enough and can be configured for .08uF which would get you into LTR for the static gap. So you won't have to worry about running STR on the PT. I'm not sure on the current rating of the PT, but I expect it's 200mA to 300mA output in which case the resonant value is .037uF to .05uF. So probably a good idea to parallel the two caps.

The static gap is of course easier and less expensive. The main consideration is high air flow and large surface area for the electrodes. Static gaps work great as long as they don't get hot. Of the various static gaps I've tried out, most were marginally acceptable. Oh they worked, but they did get hot and were difficult to control the temperature. This directly affects spark length. In this RQ arrangement and with using large diameter tubes, the cooling was no problem. This is that same static gap that I've run for those long continuous runs with.

The fan uses a 120Vac motor. I run a separate 120V line to the fan (because I use a variac for the NST input). I'm not sure of the CFM but this squirrel cage type fan pulls a good deal of air through the gap. The way I epoxied the pvc to the fan just made it simple and ensured all the air pulled was through the gap itself. You might consider a little longer tube length with the PT like about 4". I think the tubes I'm using are 2.5" lengths. It's certainly easy enough to build and try out. It's nice not having to do anything special except to turn on the coil. BTW, even though I have the ability to easily clean the electrodes, I never have. They've ran like that ever since.

The idea of inserting the electrode assembly into the pvc housing was just stumbled upon (just happened to fit). I was looking for a method to compare electrodes back when I was trying out the brass stock with minimum effort. As soon as I realized this piece fit in that piece nice and snug, the solution was then obvious.

Here's a schematic of that coil.

Take care,

David Rieben wrote:
Hi Bart,

Although I realize that the air cooled sucker gap idea is no new idea, I really like the looks of your personal setup. I now have a medium size coil on the drawing board - one that I can plug into a standard 120 volt outlet ( ~2 kVA). I have already wound 29.5" of #22 magnet wire on a 6.5" OD PVC form (~ 1050 turns) for my secondary coil and have recently obtained a 14.4 kV (120:1) GE potential transformer which I intend to use for the power source (you know how I despise NSTs). I plan on ballasting the PT with my 12 KVA rated staurable reactor. I also have a couple of extra .04 ufd, 40kV rated RFI recon mica pulse caps of which I plan on using one or both of for my primary cap. Anyway, I was trying to de- cide whether I want to go with an SRSG or a robust air-cooled stationary gap. I know the SRSG would allow me to run with a
larger primary cap and get a slightly longer output spark at a giv-
en power level but the air cooled stationary would be simpler to construct and the preset gap spacing would automatically control
the voltage rise.  I haven't constructed the primary coil yet but in-
tend on probably using standard 1/4" refrigeration tubing for 10 to 12 turns in the standard Archemidian spiral with ~3/8" turn/turn spacing. I also haven't tried to crunch the numbers with your Java- TC yet - haven't gotten that far yet ;^) I was just wanting to ask what your suggestion would be - should I go SRSG or air-cooled gap for this coil setup? Of course all others are welcome to share
their comments as well ;^)

David Rieben

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