888 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



Table I — Tube Characteristics, Design Center Values, 



New Tubes 



Heater voltage 



Heater current 



Plate -cathode voltage . . 

 Screen-cathode voltage. 

 Grid -ground voltage — 

 Cathode bias resistor. . . 



Plate current 



Screen current 



Transconductance 



Plate resistance 



Grid-cathode bias. . 



437A Triode 



6.3 volts 

 0.45 amperes 

 150 volts 



— volts 

 9.0 volts 

 262 ohms 



40.2 milliamp 



— milliamp 

 47.0ma/volt 



970 ohms 

 1.5 volts 



Capacitances (Approximate hot values in mmf ) 



Grid to plate 



Grid to cathode and screen. . . 



Grid to heater 



Plate to cathode and screen . . 

 Heater to cathode and screen. 

 Heater to plate 



3.6 

 16.4 

 0.1 

 0.7 

 5.4 

 0.2 



Modulation* 



Second order (2F) 



Third order (3F) 



Third order "effective' 



(3F) 



Equivalent noise resistance, ohms 



36 db 



67 db 



60.5 db 



* Ratio of product to fundamental at output for a 0.1 volt rms signal from grid 

 to cathode. 



complexity greatly when sockets are used. The small gain in reliability 

 would not compensate for the degradation in performance caused by the 

 complication of wiring and the resulting capacity penalties. 

 The applied voltages and current drains are shown in Table II. 



Heat Dissipation 



III common with many modern designs with high gain vacuum tubes, 

 the problem of heat dissipation was acute in the L3 amplifier. The am- 

 plifier is enclosed in a sealed housing of sufficient size to dissipate readily 

 the heat generated. However, with the usual types of chassis and tulx^ 

 shield construction, vacuum tube envelope temperatures were so high 

 that long tulx* life could not be assured. Consequently a new type of tube 

 shield w.is developed. This shield is of heavy copper tubing equipped 



