Sound-Powered telephones made of ALUMINUM.
Sound-powered are a particular type of telephone that does not require any power source to operate. They do not have electronic circuits, but are equipped with telephone capsules that can generate an audio signal simply by using the energy of the...
Sound-Powered telephones made of Glass Reinforced Polyester (GRP).
Sound-powered are a particular type of telephone that does not require any power source to operate. They do not have electronic circuits, but are equipped with telephone capsules that can generate an audio signal simply by...