Re: coax cable , blumlein, etc.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Gerry,

On 14 Nov 2005, at 11:04, Tesla list wrote:

> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Malcolm,
>
> I thought I accidentally deleted this post, but fortunately I found
> it.  I presume the excessive voltage was at the safety gap???

Yes.

> >Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>
> >
> >The "safety" gap was set wide - about 20% wider than the main gap,
> >the sparks were jumping with ease and there were plenty of them. The
> >energy was low indicating that the primary cap was not the source -
> >it was effectively shunted by the main gap. I've no doubt residual
> >energy in the transformer was a contributor but the gap firing was
> >generating frequencies that were bringing things into the
> >transmission line realm.
>
> How wide was the safety gap setting and where was it relative to the
> main gap and the coax and at what end???

It wasn't coax - just two poly-insulated coax cores - two unshielded
wires in effect. I don't know the width of the safety, just that it
was set considerably wider than the main gap.

> >I did have an RC filter of sorts at the main gap. The resistors were
> >wirewound 25W types so they were inductive to a degree. However, the
> >lines would have been contributing considerably more inductance.
>
> Can you describe where the R and C in the filter were in the filter
> and what values they were???

You'll have to forgive me - it was a long time ago - last century in
fact. The filter had a series resistor in each leg about a foot from
the main gap and a barium titanate doorknob of several thousand pF
from the transformer end of the resistors to a common centre ground,
also the transformer secondary common. Resistor values I don't
remember sorry.

> Any idea what the overvoltage frequency was and the resonate
> frequency of the TC??

The TC was several hundred kHz, the frequency at which the power feed
lines rang I never got to measure. I got about 5 seconds to observe
the discharges before the transformer died.

> Also an estimate of the coax length??

About 8 - 10 feet from memory. It was a configuration I shunned
thereafter. I reasoned that keeping the lines from the transformer to
the main gap short (about 1 foot or so which meant positioning the
transformer more-or-less right up to the main gap) obviated the need
for both a filter and a safety gap and have had no trouble since. The
downside of that strategy is having to ensure that output discharges
don't hit the transformer frequently if at all. Sitting the
transformer/s on the concrete floor would have provided some degree
of protection from the output discharges had they hit the case. I
always grounded my transformer cases to the mains ground.
     To summarize: since keeping the transformer/s position close to
the main gap I have not had a whiff of trouble.

Malcolm

P.S. - with regard to the topic of wallplug vs primary power I
mentioned in a couple of previous posts I realized for the first time
that there were major efficiency issues going on with transformers,
ballasts and spark gaps and thought at the time that it might be
possible to get to 10' from 2.3kW (the rating of a standard wallplug
outlet here). There appeared to be major discrepancies between
primary power and wallplug power. I also realized that some form of
solidstate coil would be necessary to get there if it could be done
(I started thinking in terms of switchmode cap chargers and built a
transformer but never got around to building the rest of the supply).
I now think that was overly optimistic but haven't entirely lost hope
and watched Marco's results with much interest.