468 



Popular Science Monthly 



Making a Simple Alternating 

 Current Rectifier 



A RECTIFIER is very convenient if 

 audion storage batteries are to be 

 charged and only alternating current is 

 available. The ones on the market are 

 rather expensive, but a simple apparatus 

 can be made by anyone at small cost. 



Thoroughly clean worn-out Sampson 

 sal-ammoniac cells. Cut some sheet alu- 

 minum \/2>2'' thick, the same size as the 



Jupp/i/ 



AC. 



A ^ 

 V 1^ 



Output 



Fig. 1. How the jars are connected 



zinc plates which belonged to the cells. 

 These aluminum plates should be fitted 

 into the old slots occupied by the zinc, 

 and wires carried from them up through 

 the holes in the jar covers, to serve as 

 binding posts; or the old binding posts 

 may be aluminum-soldered to the alumi- 

 num sheets. Insulate the aluminum by 

 wrapping a few rubber bands around the 

 carbon terminals. 



Prepare an electrolyte by dissolving 

 aluminum sulphate in cold tap water to 

 the point of saturation. Fill the cells 

 v/ith this solution to the water level, indi- 

 cated by a line about IMi"' from the top; 

 the two poles are then completely im- 

 mersed. Connect the jars as shown in 

 Fig. 1. 



The operation of the rectifier is based 

 on the principle that for every half-wave 

 a film of oxide is formed on the surface 

 of the aluminum, preventing the flow of 

 negative current. A rectifier of 1, 2 or 4 



/ii 



\ \ 



jars can be used, but neither the one nor 

 the two-jar type will have 80 per cent etfi- 

 ciency. The one- jar type rectifies only 

 one side of the wave. These types are 

 shown in Figs. 2 and 3. 



A Tuning-Coil Slider 



THERE are many kinds of home- 

 made tuning-coil sliders, but most 

 of them have faults. 



The most troublesome part is usually 

 making the contact strip and fastening 

 the handle. Since this requires almost 

 constant use, it must be reHable and ca- 

 pable of working easily. 



A good plan is to take a piece of 

 square brass tubing, about 3'' long, and 

 with a sharp hack-saw, slit down IM2'' 

 on both sides. Then bend both parts, one 

 up, the other down, and cut out the re- 

 maining piece inside, leaving two curved 

 arms. 



Now drill a 11/64'' hole at the end 



Slicker' 



Figs. 2 and 3. Wiring for one and two- 

 jar types of rectifiers 



A simple and efficient tuning-coil slider 



of the upper arm, and with a sharp- 

 pointed center-punch, make a small dent 

 at the end of the lower arm, to form an 

 excellent contact point, being much better 

 than a drop of solder, since that is al- 

 ways liable to chip off. An 8-32 screw 

 passes through the upper bent piece and 

 serves as a fastening: for the handle. 



Radio's First Rescue 



THE sinking of the S. S. Republic, 

 which struck the Florida during a 

 heavy fog, occurred in January, 1909. 

 This was the first ship whose passengers 

 and crew were saved by radio from what 

 would have been almost certain death. 



