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Re: [TCML] NST rebuild good

Hi Marko,

Glad to hear the rebuild went ok. As far as current, your in the neighborhood. There is a little nonlinearity with the change in voltage but not a great deal. Magnetization of the core changes with current and of course the current changes with voltage. On my NST, coupling peaked at about 80V. I did a test some time ago on my 12/60 changing voltage in 10V increments via a variac allowing me to get up to 140 input.

So the bottom line is it is hard to be exact, but your numbers sound good to me. The transformer is now an NST beast! But will always be sensitive to over-volting (so keep that in mind when running the coil).

The cap is totally STR by about 1.7 ratio. I don't see a problem with that, but I do see a problem with your main gap (and this is probably what killed the NST in the first place, especially if the safety gap was wider than it is now). The question I have is why isn't the main gap firing? How is your main gap configured? Total gap spacing? Also, what type of electrodes are you using for the safety gap? It sounds to me like your safety gap is simply arcing sooner than your main gap. Safety gaps may pop now and then, but not like a firecracker. If that's the case, the main gap is not performing it's function.

Take care,

mark olson wrote:
Hi all,

My NST rebuild worked out very well. The procedures I used were very similar to the ones that Bart has on his site. Originally the transformer was 120mA @ 15kv. During surgery I had to remove almost 1/2 pound of overheated secondary wire. The damage was too great to count layers, so I used a scale to make both secondary windings equal. The shunt stack was originally 3/4" thick. I reduced it to 3/8" thick and installed spacers to fit the windings
back on.

Now the transformer is 100:1 with about 4% difference in the secondary voltages. Note that I do not have a suitable voltage divider, so my next statements are "figgered". My voltmeter goes to 600. I applied 5 volts to the primary and got 248v from one side and 252v from the other side, 500v across the secondaries, so i figure 100:1 or 12kv @ 120v in. The current on the primary side is 26 A at 120v with an arc drawn. This is where I may be mistaken, but simple math would indicate that the transformer is now 260mA @ 12kv

Am I making mistakes in my calculations?

Here is the next part. I set the safety gap according to the recommendations of list members, the gap is now fixed at 0.250" I have not changed my capacitors yet, they add up to 0.033mfd, which, if my transformer calcs are correct, is a way too small cap. I wired the variac to 120v to stay on the safe side, and fired up the coil. Now, when I turn the power up to about 80v, the safety gap fires like a string of firecrackers. Is this because the cap is way too small? Adjusting the sync. on the rotary gap has some, but very little effect.

If I get past the safety gap issue and rewire the variac to 140v then my NST primary current would be 30 amps!
Do  you think power correction caps may be in order?



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