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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).
"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:
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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