From Telegraph Lore, a KOB set “consists of a leg style key and a telegraph sounder attached to a wooden base. The key and sounder are connected in series, and the connections to the telegraph wire are made to the two binding posts at the rear of the board. This makes for a reasonably compact portable set. Most KOBs found today are ‘practice sets’. A practice set is a relatively cheaply made KOB intended for practicing the sending and receiving of Morse. Common practice sets may be distinguished from professional sets by the three binding posts. Thus three wires connected the two sets. This allowed the use of dry cell batteries without quickly draining them as would occur with a closed circuit telegraph.”
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