RE: Terry's Calc's, my stupid mistake.

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

Original poster: "Simon Yorkston by way of Terry Fritz <twftesla-at-uswest-dot-net>" <quantumx-at-ozemail-dot-com.au>

Hi all / Terry

Well, this is an embarssing email to send, one mistake has cost me quite a
bit of money, by the sounds of it. Anyone want 12 0.047ufd caps? :)

I'll see if I can break this into bite-sized chunks.
>The protection filter numbers don't seem right.  You want about 5K with
>about 0.5nF of capacitance per leg.  Two resistors in series will give 6K
>at 22 watts which should be fine.  You gave the capacitance as "6*0.47 ==
>0.282 ufD".  If the individual caps are in series, the value is divided by
>the number of caps.  I'll assume you meant 6 caps in series at 0.047uF each
>which would give a value of 0.047/6 == 0.00783uF which is about 10 times
>too much!  You want 0.0005uF or close to that.
You know, I really want to give myself a hard slap. Looking [properly] at
your NST protection filter diagram, you implement 0.0033uFd capacitors.
I misread that to be 0.033 ufD, and not being able to get those, compile the
problem by getting .047uFD caps. Sigh. My only excuse is that this was the
first thing I built, so..It looks like a costly mistake.


>http://hot-streamer-dot-com/temp/SimonDiag.gif
>The top terminal looks too low and maybe the dimensions were not right.

Well, I daresay there was a problem in my measurements. From the top of the
secondary, to the center of the smaller toroid, there is a gap of about 2",
basically saying that the toroid is very close to the top windings. [That is
silly, I know] I just have the second toroid resting upon the first. I do
beleive, however, that the measurements of the toroid dimension was correct.

>However if I were to guess at the correction the Fo frequency is probably
>around 155kHz.
>So there is a big problem.  The primary is tuned to 191kHz and the
>secondary is 155kHz.  There are two ways to fix that.
>1.  Remove the top most terminal and leave the small one as is.  This
>lowers the secondary capacitance and raises the frequency of the secondary
>to be closer to the primary.  If the top terminal is removed, I get Fo =
>209.6kHz :-))  Now you can tap your primary in a little and hit that.  That
>will be at around 14.75 turns.
>
>2.  Increase your primary cap size.  That will lower the primary frequency
>and again bring you into the range where you can tune by taping the primary
>coil down.

 As I said, I have more capacitors ordered, which should help this along a
lot.


>It is a bit scary turning these things on full power the first time without
>a variac.  Run for very short bursts until you are sure everything is ok.


>I guess I don't know what a "SSPG" spark gap is ?:-|  What does "SSPG"
>stand for?  The gap should be fine in any case.

Again, my mistake of an extra 'S'. The gap is a static spark gap.

Thanks,
Simon