Re: NST Life Expectancy

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Wizzard,

At 01:55 AM 6/13/2003 -0400, you wrote:
>My 4" coil and had one of the NST's die.
>I suspect my protection circuit was the cause.
>I made a Terry filter and put it on my remaining NST.
>I believe the second transformer has now failed.

Could the protection circuit have failed and the NST is ok??  The Terry 
filter is designed to "die first".  The MOVs will eventually go to a 
shorted condition if the voltage is allowed to get too high thus protecting 
the NST.  You might try (carefully!) arcing each end of the bare NST to 
ground to be sure it is dead.

>I'm new to this game but I think a transformer should last more than a 
>couple minutes of operation.
>What is the normal life expectancy of an NST?

With the Terry filter, they should last forever.  there is always a 
"chance" that the NST was on the way out regardless, but the filter really 
should save it.


>The second 15KV/30mA transformer was doing great. The coil was tuned and 
>my new RQ gaps were opened full..
>I could hear some internal arcing inside the NST case and could smell a 
>burning smell.

The MOVs on the filter should have gone up in smoke long before that!

>I pulled the top off the transformer immediately and some smoke/steam came 
>out as I lifted the cover.

Oh!  That is not good ;-(  I assume it did not get water into it or 
something like that.


>I could see the tar had cracks just like the last one that failed.

That is fairly common and usually not a worry.

>This time there was a small hole where what looked like water had 
>condensed around. The liquid was also condensed on the top that I lifted 
>off. The transformer case was quite warm if you grabbed the case.
>What is happening?
>How can I stop this.

Double check your Terry filter to be sure it is made right.  Double check 
the safety gap setting too.  The filter should have saved the NST, but 
maybe the NST had water in it.  Perhaps if the NST were to dry out it would 
work again, but that is a long shot.

Cheers,

         Terry


>A quickly going broke coiler... LOL!