David Clark headsets have been found with United
States
Instruments
(USI), Stromberg Carlson, Sound Powered Communications, and Dynalec
elements
in them. This is why there is so much difference of opinion as to how
good
they work with crystal radios.
This is the best history to show how David Clarks (DC)
used
the different
elements.
United Stated Instruments (USI) was bought out by
Stromberg
Carlson
(late1950's). USI and Stromberg are the same (handset) elements. There
is two versions of stromberg/USI handset, older (the mic and ear
elements
are different) and newer (the mic and ear elements are the same).
Stromberg Carlson made elements for Dynalec, David
Clark
(DC), and
Sound Powered Communications (SPC) until they stopped making elements.
Dynalec went on to make the elements themselves. They
changed the
interior a bit when they started making their own elements.
David Clark started using Dynalec elements and some
elements made
by someone other than Stromberg/USI, not sure who they are yet, but
they
had Stromberg or USI on the housing.
Sound Powered Communications (SPC) went on and bought
out
Wheeler,
which was a knock off of the Stromberg/USI element (outside). David
Clark's
headset have been found with SPC elements inside also.
United States Instruments (USI), Stromberg Carlson,
Dynalec, Sound
Powered Communications (SPC), Wheeler, and David Clark elements all are
very similar in size and looks. In fact they are all almost
interchangeable.
David Clark Models
H5010, H5020, H5030, H5040, H5042, H5090
H5010 - double ear housing with Noise-Shielded
Microphone
H5020 - same as H5010 except headband is made to go
around the
back
of the head
H5030 - double ear housing with acoustic boom
H5040 - same as H5030 except headband is made to go
around the
back
of the head
H5042 - headset is incorporated into a face mask for
ventilation
H5090 - single ear housing with acoustic boom
The element that is the best for use in crystal
radios is
the USI
or Stromberg Carlsons. However the others work well also. You can
change
out the elements to the USI/Stromberg Carlsons if you want to. The
USI/Stromberg
Carlsons elements measure 1 to 1.3 k ohms ac (impedance) at 1 kHz. each
element.
Setting them Up
All of the elements (all brands) are wired in
parallel
except the
H5090 which is a single headset. All double elements should be
rewired
to be in series for best results in crystal radios.
David Clark H5030 (double), H5040 (double), and
H5090
(single)
units have an acoustic boom microphone. The element on the boom mic
side
is reversed and faces the boom mic tube. The back of the element has a
hole drilled in it to allow sound to the ear. You should reverse this
element
and cover the hole in the back of the element housing. The boom (mic
tube)
can be removed if you like as it will only funnel sound into the
element
housing.
Shown below is a single ear unit with an acoustic mic
(model
H5090),
but is typical of the setup of all acoustic mic units.
You will notice #6 is the element. Notice it looks
just
like a USI
element and it is pointed at the boom mic. Is does not show the hole on
the opposite side.
Here are a few comments by Robert Cullen on the conversion
of these units.
"I
got
the bracket in from David Clark so I could turn the backwards element
around, patched the hole in the back of the element, removed the boom
mike, patched the hole in the muff for the boom mike, removed that wind
muffler cap, and wired them in series.
The
folks at David Clark
are very nice and the parts are cheap. The bracket was a couple
of bucks
and I replaced the foam in the muffs while I was at it for a few more
bucks. I think it is worth the money to get the bracket to turn
the
element around and mount it securely."
Robert
Cullen
The H5010, and H5020 models use an actual element for
the
mic. It
does not have to have any of it's elements reversed, but just needs to
be rewired in series. Also all you need to do is remove the mic unit
which
plugs in anyway.
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