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Setup A Set Of David Clark Headsets

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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