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

Hello All,

My 8" coil used a single gap of 1" brass dowels on threads (easy adjustment
and cleaning) ( somewhat obscure RQ) blown by a powerful leaf blower coupled
to a 12" long 3" to .5 inch nozzle. It quenched a 15KV/120ma very well.
Since I have acquired a 14400/5KVA PT (GE), it is torn down for a rotary

I am going to experiment with a static gap much like Bart's which will be
blown by a pair of side x side pancake blowers (a lot of air). To focus the
air across the bottom, assuming it will rise just fine, I cut a 45 degree on
the face of the phenolic which is tapped and threaded to except the copper
tubes. The clincher is, I beveled the top edge to create a Bernoulli effect
and the air stays exceptionally well focused across the tubes mounting
surface rather than traveling up and away before it reaches the length of
the tubes. I'll post results when it runs.

Jim Mora     

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of bartb
Sent: Saturday, January 12, 2008 9:21 AM
To: Tesla Coil Mailing List
Subject: [BULK] Re: [TCML] copper tube stationary gap - was: NST rebuild
Importance: Low

Hi David,

The piping I bought was from Ace Hardward. 1.25". If you have 1" pipe 
stock, use it. It should do fine.

I'm using a 6.25 x 21 inch toroid on a small 4.5" diameter coil. Scale 
that up to you your 6.5" diameter and I think the 8x30 would be appropriate.

Take care,

David Rieben wrote:
> 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@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.
>> http://www.classictesla.com/photos/ba45/sch45.pdf
>> Take care,
>> Bart

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