406 BELL SYSTEM TECHNICA L JOURNA L 



of the capacitances. Not only must the capacitances be held within the 

 limits of the test specification, but the product averages must be kept close 

 to the design center values particularly in the cases of the input and output 

 capacitances. 



Table n 



• 



Heater Rating 



Heater voltage 6.3 volts, a-c or d-c 



Nominal heater current 0. 175 ampere 



Maximum Ratings {Design-center values) 



^laximum plate voltage 180 volts 



Maximum screen voltage 140 volts 



Maximum plate dissipation 1.7 watts 



Maximum screen dissipation 0.5 watt 



^Maximum cathode current 18 milUamperes 



^laximum heater-cathode voltage 90 volts 



Maximum bulb temperature 120°C 



Operatikg Conditions and Ch.aracteristics 



Plate voltage 120 



Screen voltage 120 



Cathode-bias resistor 200 



Plate current 7.5 



Screen current 2.5 



AmpUfication factor 1700 



Plate resistance 0.34 



Transconductance 5000 



Interelectrode C.ap.acit.ances {With JAN lA Xo. 314 shield connected to cathode) 



Control grid to heater, cathode, screen grid and suppressor grid 3.90 /i/if 



Plate to control grid 0.01 AJ/xf 



Plate to heater, cathode, screen grid and suppressor grid 2.85 ju/xf 



6. Conclusion' 



The important factors to be considered in evaluatmg the suitabiUty of a 

 vacuum tube for broad band IF use in the V'HF range are as follows: 



1 . Band merit 



2. Noise figure 



3. Input conductance 



4. Power consumption 



5. Physical size 



6. Control of capacitances 



We have seen that the tube design features which make a tube good on 

 the basis of these requirements are close grid-cathode spacing, fine grid wires, 

 short lead wires, and small elements. An important consideration from the 

 manufacturing standpoint is the control of cathode emission for low noise. 

 It has been possible to extend the useful frequency range of conventional 

 receiving tubes up through the \*HF range and somewhat higher by this 

 line of attack. 



