RE: Well, I know what's wrong - My brand new NST fried!!

["David Dean" <deano-at-corridor-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Garry,

>From your description of the problem I would guess that it is most likely a
carbon track in the tar. I have unpotted several NSTs and a couple of other
things in the last couple of years. Of course none of them were worth trying
to fix, they had burned up secondary coils, but the last time I bought a new
NST (with the fancy new sec. GFI thing in it). It was a good deal on ebay,
$41.00, and I figured that I would have to unpot to get rid of the safety
garbage. I didn't. Just put a jumper between the neutral connection to line
and case ground and it worked just fine. Of course the old adage "if its too
good to be true,..." holds, the NST had been dropped and one HV bushing was
bent down a bit. That would indicate a fracture in the tar around that area.
Well, to make a long story short, it only took one primary strike to kill
it. So I stuck it in the oven. When everything was melted, I discovered that
my welding gloves had "taken a walk" so I just turned the oven off. Six
weeks later, I don't cook, I remembered the NST in the oven. Figuring it
must be cool enough to touch by then I took it out, removed the transformer
from the can, documented the wiring for the safety B.S., cut it loose and
hooked the inside taps of the HV windings to the core ground terminal, (like
a pre-safety NST), set it up on top of a plastic tool box with a variac,
meter and high voltage probe, and tested. It works fine! Of course I will
not be putting the transformer back into its own case, I have an old
pressure cooker big enough to hold it, too big actually, so I'm thinking
I'll just stick it in there and run it under transformer oil.

Oh yea, you had ask what temperature and how long to cook. I use the lowest
setting the oven has, about 150degF, and let it go a couple of hours. I have
had to up the temperature on a couple of old dried out transformers, but
yours being new I would think that would not be necessary. Be sure to line a
pan large enough to hold the contents of the NST with foil and place it
under the transformer. You don't want to get tar in the oven, it does make
for a smell that is not conducive to a good appetite should you ever want to
use the oven for its intended purpose. I have found that there is not much
smell at 150 degrees however. It is only when the tar gets hot enough to
start smoking that it starts to stink.

As to removing the shunts, that is not within my realm of experience, so I
will have to defer that one to others.

best of luck,
deano


> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Tuesday, August 22, 2000 10:25 PM
> To: tesla-at-pupman-dot-com
> Subject: Well, I know what's wrong - My brand new NST fried!!
>
>
> Original poster: "Garry F." <garryfre-at-pacbell-dot-net>
>
> Thanks to the kind advice of someone who told me to test both
> sides of the NST
> for a short, I found one side barely produced a spark.
>
> To say I am disgusted, is an understatement. This is the same
> disease I always
> dealt with is the NST's frying and is what made me stop coiling for two
> decades. It's exactly what I wanted most to avoid in coiling and
> well, I think
> I will be trying a safety gap design.
>
> All may not be lost on the NST tho, I have it in the freezer and
> am going to
> freeze it and then run  it for 20 minutes and depot the thing.
>
> I also heard I could just put it in the oven and possibly melt
> the short IF it
> is in the tar. Trouble is, I don't remember how long or at what
> temperature to
> cook it. Anyone know.
>
> If I go ahead and depot the thing I am hoping I can remove the
> shunts and get
> some more current out of it.
>
> Maybe depotting will help prevent lessen the chance of future frying.
>
>
>