Popular Science Monthly 



787 



Audion of Increased Sensitiveness 



r 



New Audion Bulb 



"N the attempts 

 to increase the 

 sensitiveness of 

 audion detectors 

 and amplifiers, 

 there have been 

 devised many in- 

 ternal arrange- 

 ments of the three 

 usual elements 

 (grid, plate and fila- 

 ment). In some, the 

 spacing of the con- 

 ductors is changed, 

 and in others the forms of the electrode 

 are radically different from those usually 

 encountered. A type of tube shown in 

 the diagram, was patented by A. McL, 

 Nicolson in 1915. It is illustrated in 

 the diagram accompanying specification 

 No. 1,130,009. This instrument con- 

 tains within its evacuated bulb two 

 concentric cylindrical electrodes, of 

 which the inner i corresponds to the 

 grid and the outer 4, to the plate of the 

 ordinary audion. The filament 2 is 

 wound spirally around the inner elec- 

 trode in a groove 3, but is, of course, 

 insulated from the surface supporting 

 it. The construction shown is said to 

 show increased efficiency because the 

 filament is placed close to the input 

 electrode i and because this electrode is 

 of large surface; these two conditions 

 co-operate to set up a strong electro- 

 static field between the filament and 

 the grid or its equivalent, and this 

 has been found to make for increased 

 amplification. 



Constructing a Variable Condenser 



A VARIABLE condenser, cheap and 

 easily made, requires the following 

 materials: tinfoil, 2 ft. of }i-\n. ash or 

 oak, and 9 plates of glass, such as old 

 photographic negatives. The plates 

 should be 2>% ins. by 4>i ins. 



Cut 18 rectangles, 3^ ins. by 2^i ins., 

 of tinfoil. Shellac them at the center 

 of both sides of the glass plates. Care 

 must be taken that the foil forms an 

 even coating on the glass. Next, con- 

 struct a box of 5 sides, having the 

 following dimensions: 



Top 4^8 ins. by 2}i ins. 



Bottom Syi ins. by 2}< ins. 



Sides ^yi ins. by 3 ins. 



Back 2% ins. by 3 ins. 



Before assembling the box, make 

 9 cuts lengthwise across the top and 

 bottom, 3/16 in. apart and H in. deep. 

 The first groove on the top and also on 

 the bottom should be made }4 in. from 

 the edge. These grooves will be the 

 correct width to hold the plates firmly 

 in place, if made with a rip-saw. The 

 2nd, 4th, 6th and 8th grooves from 

 either side must be somewhat wider 

 than the others so as to allow the plates 

 to slide along easily. The top and bot- 

 tom of the box are glued and nailed to 

 the sides, as shown in Fig. i. 



The back is put on after clips have 

 been fastened to the ist, 3rd, 5th, 7th 

 and 9th plates and a wire soldered 

 across them, as shown in Fig. 2. The 



G/ass 

 r/nibif 



fii/dder /}(7/x/^ 

 'cross p/ece 



F/g.l 



Stop d/ocA 



F7h~ 



^ 



6/aJJ p/afes 



f/g.2 



A variable condenser can be made with old 



photographic plates and tinfoil. These 



diagrams show construction details and 



the necessary connections 



second, 4th, 6th and 8th plates are also to 

 be connected together in thd same way. 



A wooden stop-block, measuring % in. 

 by yi in. by 2 ins., must now be made 

 and fastened }/s in. from the edge of 

 the end of the bottom, as shown in 

 Fig. I. A handle of hard rubber should 

 be fastened to a cross-piece, measuring 

 }4 in. by }4 in. by 2 ins., and having 

 4 grooves like the ones first made, but 

 Ys in. apart. The first should be 7/16 

 in. from the end. 



The terminals should be made of 

 spring-brass less than 1/32 in. thick and 

 bent as shown in Fig. 3. One touches 

 the tinfoil of the first plate: the other 

 touches the foil of the eight plate, as 



shown. — W. E. FiNKERNAGEL. 



