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This eventually led to Pyrox
designing the Senior Soundhead during
the late 1940s. The accompanying
photos show the prototype of this
soundhead and a modified PX5
soundhead, the latter, having a section
of the original casting cut away
allowing for an effective pull through
system installed between the
intermittent and take up sprockets of
the projector head, a configuration so
successfully used by European
manufacturers.
When I was an apprentice Radio
Mechanic at Melbourne Pyrox 1961-65,
August Hoette was then a very elderly
man who still drove his Mercedes-Benz
car, although it was mostly driven by
his Chauffeur, Trevor. Above: Pyrox PX5 Soundhead modified as a “pull-through” configuration- in use with a
“Kalee 6” Projector head.
As one of my many tasks I often
had to make up replacement Exciter
lamps for the Pyrox soundhead. This An arm at right angles at the end of With one end cut at about 60-
was done by filing the bayonet pins off the tube held a microscope eyepiece. degrees, the new felt was applied
the standard exciter lamp, then A small strip of metal cut a 45-degree starting from one internal edge of the
inserting the lamp into a brass plate angle at one end to which was attached pressure roller so as to form a spiral,
holder, before soldering the lamp base a small mirror. This metal strip with the felt was glued into position.
and holder together. mirror was inserted in place of the Most of the PX5 soundheads still in
Correct lamp alignment was perspex optical concentrator. existence today will have been supplied
achieved by using a jig consisting of a By threading a short length of test originally under the RAAF contract.
small frosted screen about 10cm square film with a 1000 Hertz track (emulsion The Pyrox name still lives on with
with a cross marked in the middle of out) over the sound drum both the gas space heaters and hot water units
the screen, (at the junction of X&Y azimuth and focus of the sound optic although the company has long been
axis). The lamp was connected to a 10- could be very accurately adjusted. absorbed into the Robert Bosch
volt supply then adjusted in the brass
Another task I often undertook was Organization.
plate so the image of the filament was
to re-felt the sound drum pressure August Hoette died in 1979 at the
central to both axes. The lamp base was
roller. This was done by stripping the age of 98 years.
then soldered into place achieving the
old worn or compacted felt from the
correct alignment for optimum sound
roller, then cutting a new strip of felt
reproduction.
approx 12 mm in width.
There was also a tool for focusing
and aligning the sound optic. This
consisted of a metal tube that fitted into
the photocell cover socket.

Above: Sound exciter lamp mounted on a Above: 1948 advertisement from Pyrox Ltd. (All Photos courtesy of Ross King)
pre-focus base.

CINEMARECORD 2011 33