Wireless 

 Commu- 

 nication 



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Electrician 



Practical Electrical Hints 



Spark-Plugs Tested Without Removal 

 from Cylinders 



THE device shown in the accompany- 

 ing drawing enables motor spark- 

 plugs to be tested without removing 

 them from the cylinders. It consists of a 



5PARK SHOWS HEI 



BAKELIZCO MICARTA 

 :OPPEn WIRE 



Connecting the parts of a spark-plug so 

 as to test for short circuit 



thill slab of non-conducting Bakelized 

 Micarta 3^^ in. long, ij-o in- wide and 

 ^^ in. thick, to one end of which are 

 attached two short pieces of copper 

 wire as shown. The wires are of equal 

 length. One end is bent around with 

 the end in a groove in the Micarta 

 slab. The other is carried along the 

 edge of the slab for a short distance and 

 then bent at right angles and forced 

 down through a hole in the slab to the 

 center of a circular opening cut in the 

 face of the slab as shown. The other 

 wire is bent in the same shape, the ends 

 within the circular opening being about 

 half the thickness of a dime apart. 



In operation, one piece of wire contacts 

 the central electrode and the other 

 the shell of the plug. If the spark is 

 in good condition, enough of the current 

 will be shunted through the two wires 

 to cause a spark to jump between the 

 adjacent ends of the wires. No spark 

 will result if the plug is short-circuited 

 and it will then have to be removed for 

 inspection.— Joseph Brinker. 



Converting a Plain Zinc-Gap into an 

 Air Blast Spark-Gap 



AN interesting suggestion for radio 

 L operators is presented herewith. 

 The spark-gap has long l)een known as 

 one of the most wasteful instruments in 

 the wireless sending set. Many ama- 

 teurs have been experimenting to reduce 

 its losses. One object of rotary gaps is 

 to prevent arcing because of the ioniza- 

 tion of the air in the gap. This dis- 

 advantage may be o\'ercome by the 

 use of an air blast gap made from a plain 

 zinc spark-gap. Remove the lower zinc 

 plug and drill a i/i6-in. hole through its 

 center, as shown by the dotted lines in 

 the drawing. Drill another hole 3 8 'n. 

 in diameter, on the side, so that it will 

 coimect with the first. A brass or 

 copper tube is forced into this second 

 hole on the side, as shown, to make a 

 tight fit. Replace the gap terminal in 

 the stand, so that the tube will project 

 out at the back. The gap is connected in 

 the circuit and a small rubber tube is 

 slipped over the brass tul>c. 



RuBBefi Host 



-CT- 



/e 'hole 



COMPRESSED AIR- 



An air blast gap made from a plain zinc 

 spark-gap as a means of reducing waste 



The air may be supplied through this 

 tuljc by a pair of foot bellows of the 

 kind used by glass-blowers. If a reser- 

 voir is added the action becomes similar 

 to that of an organ-blower. 



A still better way may be to use a small 

 tank filled with compressed air. 



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