1326 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1956 



( 



by the amount the low-level gain changes, and along the ordinate by the 

 amount the maximum output changes as beam current is varied. A 

 similar procedure can be followed for variations Avith frequency and 

 magnetic field. In all figures in this Section, parameters not being pur- 

 posely varied were held at the nominal values given on page 1315. 



Low-level Gain 



Fig. 28 shows the variation in low-level gain with beam current and 

 Fig. 29 shows its variation with helix voltage for several different beam 

 currents. Fig. 30 shows the variation with frequency and Fig. 31 the 

 variation with magnetic field. 



X 



Hz 



lUO 0.8 



ujq: 





0.4 - 



Ol 



2400 I- 



O 

 > 



2380 



H 2360 



OJ 



I 



2340 1 



6 



500 550 600 650 



MAGNETIC FLUX DENSITY IN GAUSS 



700 



750 



Fig. .31 — Low-level gain, helix voltage for maximvim gain and helix intercep- 

 tion at low signal level as functions of magnetic flux density. These measurements 

 were made using different strength permanent magnet circuits. The gain varies 

 with magnetic flux density mainly as a result of its effect on l)eam size and there- 

 fore on the degree of coupling l)etween electron stream and lielix. The helix voltage 

 varies because of the effect of beam size on QC and therefore on the ratio of the 

 optimum gain voltage to the helix synchronous voltage. 



