Re: De-tunning or what?

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Chuck,

Tesla list wrote:

> 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.

It sounds like the gap to me. You mention it was replaced with an identical
gap. It may be in the design and
therefore exhibiting the same problem. Do you have forced air blowing over
the gaps? If not, give it a try since
this is a quick and simple check.

> 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.

Well, I don't know if the chokes are the problem or not, but one easy
method to find out is to bypass them and run
without them in the circuit. See what happens.

Good luck,
Bart A.