Photograph 2: — Inside view of 

 oxygen- temperatiire meter. 



COLLECTOR 



BASE 



COLLECTOI 



BASE 



Figure k- — Lead identification and 

 schematic representation of 

 transistor. 



The wiring and lead dress are not criti- 

 cal, and the wires can be rat-nested or neatly 

 arranged. All the resistors, except the micro- 

 pot and wire -wound pot, can be mounted between 

 the appropriate switch terminals. The transis- 

 tor can be similarly soldered into the circuit by 

 attachment to unused switch terminals, which 

 make excellent tie -points. Caution: Avoid over- 

 heating the transistor. When soldering the leads, 

 provide a heat sink; i.e. place pliers or a metal 

 clip on the transistor lead between the solder 

 joint and the body of the transistor . Pay partic- 

 ular attention to the arrangement of leads on the 

 transistor and connect properly in the circuit. 

 An error here will ruin the transistor. See 

 figure 4 for proper identification of leads. Also, 

 label the battery holders, plus and minus, so 

 that the battery polarities will not be reversed 

 when batteries are replaced. A reversed 

 battery can ruin the transistor. 



CONSTRUCTION OF THE ELECTRODE 

 ASSEMBLY 



The construction of the electrode may 

 require some ingenuity on the part of the builder, 

 but a description of some of the methods which 

 we have used may be of benefit . 



An empty 12 -gauge shot gun shell is 

 ideally suited for a mold for the epoxy since the 

 3/4-inch silver tube will fit inside the 12 -gauge 

 case . To prevent the epoxy from adherring to 

 the paper, the inside of the shell should be coated 

 with vaseline or similar material (mold release). 

 A 6 -inch length of wire should be soldered to the 

 inside of the silver tube. Place the end of the 

 silver tube in modeling clay and fill the tube with 

 epoxy. Then drill a small hole (1/8 -inch) through 

 the center of the epoxy after it has hardened. 

 Insert a wire throu^ this hole and solder to the 

 center of the platinum disc. This wire should 

 be placed through the hole and fastened into posi- 

 tion in the center of the silver tube in such a 



