Re: Question on DF-DRSSTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hi Jim,

While i am not Terry, i will comment a little here.

On 12/22/05, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "James Zimmerschied" <zimtesla@xxxxxxx>
>
> Teryy,
> I am starting to put together a DF-DRSSTC based on your design. I
> would like to know why you are using a flat primary with evidently a
> low coupling as compared to other DRSSTC's which seem to be using
> helical primaries and higher coupling?

My DRSSTCs were the first to use the higher couplings.  At the time i
believed that faster energy transfer was required.  While i still
believe in using the highest coupling possible, i will say that you
can achieve long sparks in either manner.  Basically as i see it,
smaller coils work better with higher coupling for 1 main reason.  You
can detune the primary so much that the energy does not transfer to
the secondary for some time.  Eventually this build in primary voltage
results in corona forming on the secondary, lowering the secondary Q
so much that tuning is no longer crucial.  At this point all of that
built up primary energy is dumped into the secondary and streamer.
Because the coupling is relatively high, the transfer occurs very fast
at this point, which we want.  I dont know if this tuning method is
valid on the DF-DRSSTC.

Larger coils seem to work ok with lower coupling (i like to use about
.18).  With this lower coupling, i tune the coils so that notches
occure (due to frequency splitting).  I shut down drive at the first
primary notch (similar to making a SGTC with perfect quenching).  This
indicates that a full energy transfer has taken place.  This technique
doesnt work so well on small coils because you simply cant build up
enough energy before one notch with the higher frequencies.  My larger
coils operate below 60khz, and are able to achieve great bang energies
in just 6-8 cycles usually (about where the first notch occurs).

>
> Also, what are the characteristics on your secondary?

Just go for the lowest operating frequency acceptable.  My DRSSTC-1
for example uses a 6.5"x22" winding of 30awg and can produce 72"+
sparks.  I would advise going no higher than 150khz if possible
(assuming you arent trying to build a miniature TC?).  With Terry's
DF-DRSSTC, switching speed is pretty slow, so lower operating
frequencies ease the drawbacks of this.

Good luck.  If you havent had much play time with power
semiconductors, welcome to the club :-).

Steve Ward

>
> Thanks
> Jim Zimmerschied
>
>
>