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

[bartb]

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,
Bart

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 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