The antique Western Electric Polarized 7A Telegraph Sounder with 1000 ohms resistance was manufactured in the United States. This collectible piece of railroadiana hardware is a rare find for enthusiasts of transportation memorabilia. Made with quality craftsmanship by Western Electric, this telegraph sounder represents a piece of American industrial history and is a valuable addition to any collection. This sounder is used in Duplex and Quadroplex land line telegraphy. The permanent magnet biases the magnetic flux of the electromagnet so that the sounder will only respond to current of one polarity and not the other. That permitted a single telegraph line to carry 2 signals at the same time thus doubling the value of that line… $25