Re: De-tunning or what?

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

Original poster: "Peter Lawrence by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>

Chuck,
      this is the sort of behavior I get with a spark gaps that don't have
enough gaps, in other words 6-segment multi gap would do this but 12-segment
multi gap might not. I suspect it has to do with gap electrode heating. If
your gap spacing is adjustable, then put your stand-by unit in series with
your first one, and halve all the gap spacings, then see what happens.

I've had this problem with brass and stainless steel, but not with tungsten-
carbide. Tungsten carbide is the opposite that until the electrodes heat up
they work best with a wide spacing and then as they heat up the gap has to
be closed down.

(YMMV, I've never used more than a 9-30 NST)

The other possiblity is if you use ceramic caps in your primary they can
heat up and de-tune. Polypropylene caps don't seem to have this problem.

-Peter Lawrence.


>
>Original poster: "Charles Hobson by way of Terry Fritz <twftesla-at-uswest-dot-net>" 
<charles.a.hobson-at-btinternet-dot-com>
>
>Hi all,
> 
>When I power up my coil (using a NST 10kV/60mA)  I get massive sparks into the
>walls and ceiling which are only about a meter away. The room is not ideally
>suited for this so I don't know the maximum possible spark length. Anyway,
>after about 5 seconds of power application the sparks wane considerably
and the
>safety gap (15mm) takes over. I switch off power for several seconds and
>re-apply it to get the same big sparks. As I  repeat this process the time for
>the safety gap to take over reduces to about 1 seconds. If I then wait a
minute
>or so, the process repeats all over again starting at 5 seconds of power
>application etc.
> 
>I thought it was my spark gap crudding up, so I replaced it with my standby
>unit. Both are identical static 6 segment multi-gap units. Nothing changed.
> 
>I am not certain but it appears that the secondary coil is becoming
de-tuned by
>something which happens during operation and that the energy released in the
>primary (100/sec.) is reflected back to the NST via two 2mH chokes. The
>operating frequency is 109kHz. That is, primary and secondary coils
>independently are pre-set to this frequency +/- about 500Hz. The coupling k is
>0.19. 
> 
>I would be most grateful for any comments
> 
>Chuck/England  
> 
>     
>
>
>