From: "Malcolm Watts"
Date: Mon, 13 May 2002 09:34:35 +1200
Subject: Re: [TSSP] Topload breakout potentials
Hi John, all,
On 12 May 2002, at 9:28, FutureT@aol.com wrote:
> In a message dated 5/11/02 6:32:04 PM Eastern Daylight Time,
> paul@abelian.demon.co.uk writes:
>
>
> > Tuning low seems to keep quite a lot of energy in the primary,
> > thus reducing the peak topvolts but perhaps enabling the beat
> > envelope to be sustained over more beats, thus generating
> > fewer streamers but allowing them to grow longer. Is this a
> > recommended way to deal with a too-small topload?
> >
> > Paul,
>
> I've never really heard the issue discussed much before. It seems
> that Malcolm's toroid on his coil has such a large ROC, that
> it may be tuned correctly, yet still barely breakout. This may
> be why he's getting such good results. It would be interesting
> to see if Malcolm's coil's tap points, etc. indicate a perfect tune
> between pri/sec. Probably you've calced all that anyway
> Malcolm? If Malcolm's coil calcs out to be tuned, this would
> suggest the tuning model is working well. Even if Malcolm's
> primary is tuned lower than Fsec, it may be *closer* to a
> proper tune than my TT-42.
>
> Cheers,
> John
My coil is pretty much primary Fr = secondary Fr. I don't have a lot
of latitude for tuning since the primary has 5 turns and all are used
(about 16uH and Cp 100nF, secondary+topload running at 130kHz).
Right now, I don't have anywhere to fire it either. I could maybe get
some lab space in a semester break. I would like to add an even
larger topload (I have one waiting in the wings) and another primary
turn. All has been achieved with a rather dinky transformer (custon
wound).
On the magnifier/extra coil flashover Q, I recall seeing some
video where this was happening - might have been one of Richard
Hull's early models. I'v seen this happen on coils that are mistuned
(in general) and there has been no breakout at all.
On the downward detuning of the primary (this bit *not* related
to the racing spark issue), this is known as offset tuning (this was
related to me by a very knowledgeable coiler some years ago). I
discovered this for myself one day and put it to the list for
comment. The result was erratic gap firing (no special attempts to do
anything about it I'm ashamed to say) but longer louder sparks when
it did fire. The basic idea was to take advantage of the phenomenon
that mutual coupling of resonant circuits exhibits, namely double-
sideband production. The idea was to enhance the lower sideband at
the expense of the upper so the coupled response had one strong
frequency and a much weaker one above it (unloaded of course). In a
nutshell, the crude theory was to tune the primary to the lower
sideband that appeared with correct tuning. In examining the result
with sig gen and scope, I found that there was indeed an enhanced
response to the lower frequency and a much diminished one at the
upper. I have no idea what it looked like with spark loading.
Regards,
Malcolm
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.