The Construction of a Magnetic Break Key 



With it the lightest kind of a 

 Morse key may be used for sending 



By T. Lambert 



THE average experimenter's "break 

 key" consists of a number of springs, 

 contacts, etc., which are attached to 

 his regular transmitting key in a clumsy 

 manner. To send clearly a code with key 

 contacts 34 in- apart is next to impossible. 

 With the relay-key described herein it is 

 possible to use the lightest kind of a Morse 

 key for sending, since 

 all the clumsy con- 

 tacts of the breaks 

 are on the heavier 

 magnetic key. Fur- 

 ther, no heavy cur- 

 rent is handled by the 

 small key and thereby 

 arcing and sticking 

 are eliminated. 



A key as described 

 has been in use in my 

 amateur station for 

 some time and has 

 never given any trou- 

 ble in holding the 

 detector -adjustment, 

 even with the most 

 sensitive minerals, 

 such as galena and 

 cerusite. 



The completed in- 

 strument is shown in 

 the illustration. Four 

 spring-contacts are 

 employed, besides the 

 alternating current 

 break. The pair at 

 the right disconnect 

 the detector from 

 the receiver when 

 depressed. One of 

 the contacts at 

 the left shorts the 

 telephones while the 

 other one grounds the 

 entire receiver while 

 sending. It will be 

 seen from diagram B that the receiving- 

 tuner's primary is placed in series in 

 the ground-lead of the oscillation-trans- 

 former. 



When sending, the high voltage currents 

 from the transmitter pass directly across 



Four contact springs besides the A. C. break 

 are employed in this magnetic break key 



to the ground through the last mentioned 

 contacts on the key. Some stray current 

 may find its way into the receiver but will 

 not damage either telephones or detector 

 because they are amply protected by the 

 other contacts. There is absolutely no 

 danger of shock as all receiving apparatus is 

 on the grounded side of the oscillation-trans- 

 former. The magnet 

 cores are shown at C. 

 A good grade of soft 

 iron should be used, 

 as it is less liable to 

 hold residual magnet- 

 ism. The cores are 

 threaded to fit the end 

 pieces snugly. The 

 windings can be made 

 directly on the cores 

 after a layer of tape 

 is placed, but it is 

 preferable for ease in 

 winding to turn out 

 two bobbins on a 

 lathe, as shown at D, 

 and wind on them. 

 Use number 20 D. C. 

 C. wire and wind on 

 eight or ten layers, 

 placing a heavy sheet 

 of paper between the 

 layers. On the final 

 layer glue a thin piece 

 of ebonite to give it 

 a finished appearance. 

 The brass crosspiece 

 which holds the screw 

 for adjustment of the 

 tension of the spring E 

 (page 159) is shown at 

 F. The piece G is of 

 hard rubber and sup- 

 ports the stationary 

 primary contact as 

 well as the yoke H for 

 regulating the play of 

 the key. It is attached to the top of the 

 magnets with two machine-screws. The 

 armature support is cut from J^-in. brass. 

 The contact and crosspiece holes are best 

 located after it has been set up on its 

 pivot J. This is also of fcrass, cut to the 



157 



