Re: [TCML] Coil Died

[Greg Peters <greg.j.peters@xxxxxxxxx>]

Tim,

I've come into this conversation a little late and have not read each and every post as I deleted them without thinking. So apologies if this has already been said.

Firstly, check for hot turns on the secondary or blistering of the varnish, indication of a short between two adjacent turns which may be hard to see during operation due to a lack of a large spark.

Now, assuming that your secondary, primary, capacitor and transformer are all functioning correctly (did you check the xformer), you have to go back to first principles. 

The bottom line is that you have changed your system and you can't change one thing without having to properly retune and possibly alter the coupling. If you are running a bigger cap your bang size is larger and you may be over driving the secondary (and hence the racing arcs). Even if you changed your ceramic caps for an mmc of equal capacitance, it is likely that your primary inductance is also altered due to the reconfiguration. A retune is necessary.

The side effect of retuning is that it also slightly alters your coupling. So it is possible that the altered tuning required by your modifications is pushing your coil into over coupling (and hence the racing arcs). 

I would try starting from scratch. Lift your secondary up a good few inches from the primary by placing it on some kind of insulating spacer. This will let you set the tuning without fear of over coupling. Once the tune is set, move the secondary down bit by bit, each time moving the tap 1/4 - 1/2 turn either way to confirm the best tune for that setting. Work your way down, each time making sure your tune is optimal to within 1/3 turn.  Eventually you will either bottom out your secondary (first turn of secondary in line with primary), or racing arcs (over coupling) will appear. In this case it's time to lift the secondary back up a bit to the last point. Then you're set. Let us know if this works and good luck!

Greg.

Sent from my phone

> On 11 Oct 2013, at 1:14 am, Tim Flood <tfloodrr@xxxxxxxxx> wrote:
> 
> Thanks to all for your replies.
> 
> Dave, the thickness of the coil form is 3/4".
> 
> I disassembled the secondary coil to inspect the interior and found no
> signs of carbon tracking. Also ran a rag through the inside just in case
> there was any contamination. There did not appear to be any damage to the
> secondary winding.
> 
> I did remove the MMC string and re installed the door knob caps. As soon as
> I began turning up the variac little sparks developed along the length of
> the sec. winding. This sparking stopped as the voltage increased. The TC
> then performed a little better with the door knobs back in - then quit as
> far as producing arcs from the toroid.
> 
> Another bit of information. When the discharges from the top load quit, the
> firing of the static spark gaps seemed to drop in voltage as though the
> variac had been decreased by 50%. I also received a very mild shock from
> the variac body.
> 
> I did not change anything that would effect the coupling, but I will try
> some adjustments. This coil has always been a good performer. The
> performance has been slowly dropping off over the past year, though.
> Thought I had the reason why when I found the cracked primary ribbon. Now
> it acts like a completely different coil.
> 
> Could one of the two paralleled NSTs be contributing to the problem? I'm
> about ready to start over and build a completely new one, but I need this
> one in the near future.
> 
> Please keep the advice coming.
> 
> Thank you,
> 
> Tim Flood
> 
> 
> 
> 
> 
> On Wed, Oct 9, 2013 at 8:39 PM, David Thomson <
> tcbuilder@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> 
>>> On Wed, Oct 9, 2013 at 3:57 PM, Tim Flood <tfloodrr@xxxxxxxxx> wrote:
>>> 
>>> Thanks. One thing I maybe should have mentioned is that PVC tube wall
>>> thickness is about 3/4". But I will disassemble and take a look tonight
>> for
>>> any signs of arcing inside.
>> Are you saying you have 3/4" PVC between the primary and secondary?  Or is
>> this the thickness of the secondary coil form?
>> 
>> Dave Thomson
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