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Re: [TCML] Interesting historical rotary spark gap transmitter transformer.

I think they must make an air gap big or small. I use a harbor freight
welder in series with a 5kw transformer the welders low voltage secondary
is shorted. There is an adjustment knob you turn that makes a few of the
laminations move in or out to change the welder current. Which will limit
the current draw so the 20 amp circuit breaker won't trip. Otherwise when I
short out this transformer running a Jacob's ladder or Tesla coil it would
draw too much. Wanted to make my own current limiter but the hobby arc 110
was cheap.

On Mon, Jun 22, 2020 at 12:54 PM Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx>

> Hi Chris,
> I found an article that might help from a July 1923 QST article about
> how to modify a similar (Type T) Thordarson HV transformer to convert it
> into a filament transformer. In those days, spark was rapidly being
> replaced by vacuum tubes, and old spark equipment was sometimes
> "repurposed" by amateur radio hobbyists.
> Thordarson made both Type R and "Flexible" models T-1 and T-2 for the
> spark wireless market. In these transformers the magnetic circuit
> consisted of a main pair of C-cores with the primary winding on one leg,
> and the HV secondary on the opposite leg. In addition, a magnetic shunt
> (another core leg) was provided across the primary leg of the main core.
> This created a magnetic shunt what provided a flux leakage path that
> preventing some of the primary flux from linking to the secondary. By
> adjusting the air gap between the primary leg and primary shunt, the
> proportion of leakage flux, and the primary:secondary coupling
> coefficient, could be varied.
> This is similar, in principle, to magnetic shunts used in modern-day
> coil-and-core NST's. However, the physical location of the shunts is
> different between the antique Thordarson transformers and NST's. In
> NST's, the magnetic shunts bridge across legs of the main core between
> the primary and secondary windings. In the Thordarson spark
> transformers, the magnetic shunt forms an external third core leg that
> was physically external to the main primary-secondary core loop. The
> adjustable shunt is located below the primary winding in the Type R, and
> above the primary winding in Type T transformers. Otherwise, the shunts
> function similarly - reducing the proportion of magnetic flux that
> linking the primary to the secondary (and vice-versa).
> Although the following description in the QST article was written for
> the type T transformer, it should be similar (in principle) for the
> model R. See page 33 (page 35 of the PDF file) from
> https://worldradiohistory.com/Archive-DX/QST/20s/QST-1923-07.pdf
> "A filament lighting transformer can easily be made from an old
> Thordarson spark transformer of the "flexible" type. The one used to
> make the filament transformer here described was a one kilowatt type
> "T," which most amateurs of a few years standing will remember. The type
> "T" had a magnetic shunt in the shape of an extra core-leg above the
> primary. This shunt was hinged and had a wing-nut and spring arrangement
> to hold the magnetic leakage tongue (shunt) at any desired adjustment.
> This arrangement worked very well except at close settings (small air
> gap) when the rattle was terrific.
> "Accordingly in converting the transformer the spring was removed and
> the shunt set right down on the top of the main core and secured there
> by U-shaped straps of iron hooked over the shunt. These U-shaped clips
> are held in place by the bolts that hold the transformer frame together.
> It is then possible to clamp the shunt down solidly by driving wedges
> under these straps or by driving the tops of the straps apart so that
> they slant."
> Images of the type T and R transformers can be seen at the Radio Museum
> site:
> https://www.radiomuseum.org/r/thordarson_flexible_step_up_transformer_type_t_1.html?language_id=2
> https://www.radiomuseum.org/r/thordarson_spark_gap_transformer_type_r.html
> Hope this helped and best wishes,
> Bert
> --
> Bert Hickman
> Stoneridge Engineering LLC
> Woodridge, Illinois, USA
> http://www.capturedlightning.com
> +1 630-964-2699
> ***********************************************************************
> World's source for "Captured Lightning" Lichtenberg Figure sculptures,
> magnetically "shrunken" coins, and scarce/out of print technical books
> ***********************************************************************
> Chris Reeland wrote:
> > Hi all,
> >
> > Even though this has gone off in a few "tangents". I am still intrigued
> by
> > what is still going on for current control. I am curious if someone knows
> > exactly what is all going on possibly for current control.
> > I keep studying pictures occasionally... still puzzled. I look at what I
> > can see for lamination stack of the primary and what I can see of
> > mechanically adjustable part baffles me. Is there an adjustable air gap
> > introduced? Or just changing "surface" area of laminations for the
> magnetic
> > flux. And maybe "bypass" laminations underneath primary winding. Again
> just
> > puzzled on this. Where I would have thought to see some crossing of
> > different lamination stacks I am not seeing for primary to transfer to
> > secondary. Again just being curious overall on this to me interesting
> > fella... just trying to understand.
> >
> > Chris Reeland
> > Ladd Illinois USA
> >
> > Sent from my LG V20
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> >
> >
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