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

[David Rieben]

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
~$46!). 

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 ;^)

David 


----- Original Message ----- 
From: "bartb" <bartb at classictesla.com>
To: "Tesla Coil Mailing List" <tesla at pupman.com>
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.
> http://www.classictesla.com/photos/ba45/sch45.pdf
> 
> Take care,
> Bart
> 
> 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 ;^)
>>
>> Thanks,
>> David Rieben
> 
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