146 



BELL SYSTEM TECHNICAL JOURNAL 



The Deflector Elements 



The deflector plates are made of German silver, which is non- 

 magnetic and which has a high specific resistance that diminishes the 

 effect of eddy currents when magnetic deflection is used. The plates 

 are 13.7 mm. long in the direction of the tube axis and the separation 

 between them is 4.7 mm. 



The sensitivity of the tube is such that the deflection of the spot 

 is about one mm. per volt applied between the deflector plates. When 



l+7^^ 



Fig. 4 



using magnetic deflection, a pair of coils 4 cm. in diameter placed on 

 the sides of the tube at the level of the deflector plates produces a 

 deflection of approximately 1 mm. per ampere-turn flowing in the coils. 

 The electrons striking the screen drift back to the anode structure, 

 and most of them are collected by the deflector plates. There is also 

 a small ionization current flowing to the plates. The tube is therefore 

 not strictly an electrostatic device, and this must be kept in mind 

 when using it. Fig. 4 shows the current flowing to the two free plates 

 at various voltages with respect to the anode. With the large posi- 



