Tesla coil grounding and other questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: JOSEPH CACCIATORE <jocatch-at-us.ibm-dot-com> 


Hello. I am trying to resurrect my old tesla coil I made in high-school 30 
years ago with plans that came from the July 1964 Popular Electronics 
magazine. I still have the secondary coil and 12kv, 30ma NST which I want 
to use. The secondary was built pretty close to the article, 4.75" 
diameter, 34.625" long using #26 (or was it #28) wire. The NST is center 
tap to the case.

First question is grounding. The 120 vac for the NST of course is not 
grounded (only 2 leads to the outlet). The design I have shows the bottom 
of the secondary connected to one side of the primary tesla coil in an 
auto-transformer arrangement. That is how the original design worked and I 
was able to get 2 or 3" sparks from it.

But reading on the net I see some places which say ground the bottom of the 
secondary to the case of the NST only and some show the bottom going to 
earth ground only. Which is correct? If I want to run it in a house or 
display like at school, there won't be an earth ground to begin with.

Also, if you have seen the PE issue, they had the spark gap in series with 
the primary but all circuits I see on the net today shows the capacitor in 
series. Is that better?

For the capacitors, I am using thick window glass and aluminum foil, each 
glass is about 18"x18". I am using 2 of them.

Lastly, since I have about 75' of 15kv wire I want to make the primary 
using the wire in a helical coil arrangement (I don't have copper tubing 
nor anyway to bent it nor a mount for it). I assume I will need all the 
wire since my basic calculations show I would need 52 turns for the 
primary. Since 52 would require more wire than I got, could I go with a 
harmonic and use 26 turns for the primary?

Thanks for any input you guys may have. I got this beautiful secondary coil 
I made and NST and I really would like to make it work.

JC