Tools of Telegraphy
Below are images of the instruments used to transmit and receive landline Morse. I have tried to put together a good sampling of the various instruments used. There are 4 seperate pages due to the large quantity of graphics. Here is an index of these 4 pages:
Page 1- Leg Key, Legless Key, Local Sounder, Mainline Sounder
Page 2- Morse Relay, Bug, KOB, Box Relay
Page 3- Barclay Box Relay, Candlestick Resonator, Swing-arm Resonator, Cordless Jackbox
Page 4- Sideswiper, Repeater, Polar Sounder, Register, Gravity Battery, Insulators
Click on the image for a larger, more detailed look at these instruments. (Note: You might want to try turning up the brightness on your monitor to bring out the detail on these images. "Gamma" adjustment may also help.) These images are quite large to capture the maximum detail. Simply expand your browser window (click and hold on the lower right corner) to see the entire image !
This is the instrument that comes to mind first when someone mentions the telegraph. The telegraph key was invented very early in the history of the telegraph by Morse's associate Alfred Vail. The original design was called the "Vail Correspondent". The telegraph key is nothing more than a single-pole single-throw switch that is ergonomically designed for rapid opening and closing by a human operator using the tips of the fingers. The key's electrical contacts are held "normally open" by a spring. Pressing on the key's knob closes the contacts and completes the circuit. Another switch in parallel with the key is called the "circuit closer". The circuit closer is essentially a single-pole single-throw knife switch. It functions to close the circuit during the reception of incoming messages. This type of key is often referred to as a "straight key" since the dots and dashes of the Morse alphabet are formed manually by the telegrapher. The key shown is the classic "Steel Lever Key" which was patented in 1881. The lever is made from a piece of stamped steel. This is the original "leg key" version. The two "legs" are the key's terminals, and they also are used to bolt the key to the operating desk. This example was manufactured by Bunnell.
The legless key is functionally identical to the leg key. The key's terminals are located at the rear of the base on the top side of the key. This allowed the key to be mounted to any surface, and you did not have to crawl under the table to attach the wires to the terminals ! This example appears to be a military version manufactured by Bunnell.
This is a "local" sounder. The sounder transforms the current pulses in the telegraph wire into audible clicking sounds which are interpreted by the telegrapher. Two vertical solenoids form a horseshoe magnet. Current pulses energize the magnet which then attracts the armature. The armature is attached to a spring loaded lever. The lever strikes the lower portion of the anvil, producing an audible click. Another audible click is produced when the lever strikes the upper portion of the anvil upon cessation of the current. The lever has knurled screws and jam nuts that allow the spacing of the armature from the magnet and the lever travel to be adjusted. Another screw adjusts the spring tension. This type of sounder was used in a "local" circuit. This means the source of current was provided within the telegraph office, as opposed to the mainline sounder which obtains its current from the telegraph wire. Most local sounders were wound to a resistance of 4 ohms which allowed them to be powered from a single gravity cell. A local sounder powered this way makes a relatively loud sound compared to other receiving instruments such as the box relay. The local sounder was connected to the relay contacts. Thus the extremely sensitive relay controlled the local sounder. This amplifies the weak currents in the telegraph wire which allowed the telegrapher to hear the Morse messages in a noisy environment such as a train station. This sounder has no manufacturer's markings. If anyone can identify this sounder, please send a note via the "mailto" on the Telegraph Lore homepage.
The "mainline" sounder was designed to connect directly to a telegraph wire without the use of a relay. It is sort of a hybrid between a relay and a local sounder. The magnet windings are always 30 ohms or greater, with 120 ohms being the most common. The spacing of the magnets from the armature is critical in determining clear copy as the current varies. The mainline sounder was thereby designed to have easy adjustment of the spacing. This particular sounder has a spacing adjustment knob on the left. Rotating the knob causes the magnets to move up and down by means of a camming mechanism. This sounder is labelled "W.U. TEL. C.O. M.L. SOUNDER 17-A 30 OHMS". It was manufactured by Community M&T Works, but it is a Bunnell design.
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