ABSTRACTS OF TECHNICAL ARTICLES 625 



currents is described, and the characteristics of a filamentary cathode 

 tube of low microphonic noise level are given. The characteristics of 

 a double anode, thermionic, gas-tilled, rectifier tube for use in a d-c. 

 power supply unit for the sound lamp and vacuum tube filaments of 

 reproducing systems are given. A photoelectric cell of high sensitivity 

 for use in sound reproduction work is described. 



Analysis and Reduction of Output Disturbances Resulting from the 

 Alternating-Current Operation of the Heaters of Indirectly Heated Cathode 

 Triodes.^ J. O. McNally. This paper discusses the disturbance 

 currents in the output circuits of indirectly heated cathode triodes, 

 introduced by the use of alternating current in the heaters. It 

 indicates that the disturbance currents are introduced into the output 

 circuit by (1) the electric field of the heater, (2) the magnetic field of 

 the heater current, and (3) the resistance between heater and grid and 

 between heater and plate, and the capacitance between heater and 

 grid and heater and plate. 



The outputs due to the electric field between cathode and plate are 

 produced by the "grid" action of the heater and heater leads. The 

 frequency of the output is chiefly that of the heater supply. The 

 outputs are shown to be effectively reduced by electrostatically shield- 

 ing the heater. 



Disturbance currents of the frequency of the heater supply, and of 

 double this frequency are shown to be produced by the magnetic 

 field. The double-frequency component is shown experimentally to 

 be proportional to the square of the heater current. The following 

 means of reducing the magnetic field are discussed: (1) the adoption 

 of a heater geometry which produces a smaller field in the space between 

 the cathode and the plate, (2) the use of a magnetic shield around the 

 heater system, and (3) the use of a lower current, higher voltage heater. 



The ways in which disturbance currents are introduced by leakage 

 resistances and capacitances between heater and grid and heater and 

 plate are indicated, and experimental v^erification is given for the case 

 of resistance between the grid and heater. 



Use has been made of this disturbance current analysis in the devel- 

 opment of an extremely low disturbance output tube, which is de- 

 scribed. 



Fourier Series in Three Dimensions.'' W. O. Pennell. The classical 

 Fourier Series represents a function in a given interval and then 

 repeats the same values in the next and subsequent interv^als. In 



^Proc. I.R.E., August, 1932. 



' Am. Math. Monthly, May, 1932. 



