Headset 528 / 161A with SW-141-V

This headset was developed for military application - in particular for use in tanks.  It consists of a hearing capsule "528" and a tonality condensor "161A".

The DC-resistance of the hearing capsule is 55 Ω, and the induction is 50 mH (@ 1 kHz), resulting in an impedance of 300 Ω.  The capacity of the condensor is 0.15µF.  It is attached to the hearing capsule by a bayonet lock system.

Also part of the headset is a switch, model Trav-Ler Karenola SW-141-V. Switch, hearing capsule and condensor are wired in such a way that when releasing the switch handle, the condensor is put in series with the hearing capsule, thus forming a high pass filter network. This shifted the maximum of the response curve of the hearing capsule to higher audio frequencies, thus improving the understandability in high noise level environments.

When pressing the handle, the condensor was bridged, broadening the frequency response of the hearing capsule.  A small catch served to retain the handle in pressed position, giving relief to the operator's thumb during extended broad band operation.

The patent application document US 1273351 of 1918 (the number embossed on the rear of the hearing capsule) can be viewed via Internet patent servers. It shows interesting construction details of the mechanical setup.

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