Re: new coil woes

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: jdwarshui@xxxxxxxxx 

Hi Jim

Richard Quick wrote about rebuilding NST in the early Pupman archives.
Sorry I cannot remember specifically when.

NST repair is not difficult but it does take time:

This advice is general and may not apply to your transformer. I doubt
much can be done for an epoxy filled transformer, I will assume yours
is tar filled  :

Open up the wrap around top with a cold chisel or drill. Now break
away the tar edges (gradually) with a hammer until you have found the
location of the secondary windings, don't want to hit these.  Work at
removing the tar behind the porcelain insulators until you find a
metal clip.  Pull this clip out with vise grips,  unsolder the wire
behind the insulator. Now you can pull off the end tins and remove tar
as best you can with screwdrivers, chisels and hammer blows. There are
little wedges that hold the primary and secondary in place, note
location and remove these. The transformer core has eight or so bolts
holding it together. Remove these and give the laminations repeated
sharp blows with a hammer and they will separate.

I hate solvents but they are a necessary evil, Carburetor cleaner does
a nice job of cleaning the secondary.

If you break a secondary wire near the top of the windings you can
peel back paper (or fabric) and re-splice. Burnt paper on the side of
the secondary is not cause for automatic rejection, try cleaning first.

The process of tuning a coil tends to place harsh loads on tank
circuits. If you get brutal flashovers, hear popping noises, or your
safety gap sounds like a rifle. Your instincts about doing damage are
probably right on the nose. So I guess what I am saying is you have to
stop and change something when you hear odd noises or the coil is
firing  intermittently.  re-tapping the primary?  backing off the
coupling?

You can detune coils from maximum output by deliberately closing up
the spark gap (just a bit) this places less load on the NST.

It is handy to have a Jacobs ladder for testing the output of your
NST. If your transformer is failing the Jacobs ladder will confirm  it.


Jared Dwarshuis