ELECTRON TUBES FOR A TRANSATLANTIC TELEPHONE CABLE 171 



A serious attempt has been made in the design of the tube to hold the 

 number of fastenings that depend entirely on one weld to an absolute 

 minimum. The grids are of conventional form in which the lateral wires 

 are swaged into notches cut in the side rods or support wires. The side 

 rods as well as the lateral wire are molybdenum. This produces grids 

 which are considerably stronger than those using more conventional 

 materials. 



The upper mica is designed to contact the bulb and the bulb is sized 

 to accurate dimensions to receive and hold the mica firmly. The tube 

 in its mounting will withstand a single 500g one millisecond shock with- 

 out apparent changes in mechanical structure or electrical characteris- 

 tics. It is estimated from preliminary laying tests that accidental or un- 

 usual handling would rarely result in shocks exceeding lOOg. 



Electrical Characteristics and Life 



The average operating electrical characteristics for the 175HQ tube 

 are given in Table I, and a family of plate- voltage versus plate-current 

 curves for a typical tube is given in Fig. 5 for a region approximating 

 the operating conditions. 



The development of a long-life tube offers good opportunities to ob- 

 serve effects which are more likely to be missed where shorter lives are 

 satisfactory. For example, some of the earliest tubes made, after 20,000 

 hours on the life racks, began to show a metallic deposit on the bulbs. 



Table I — Average Operating Electrical Characteristics for 



THE 175HQ Tube 



Heater Current 



Heater Voltage 



Heater Power 



Control-Grid Bias 



Screen Voltage 



Plate Voltage 



Screen Current 



Plate Current 



Transconductance 



Capacitances (cold, with shield) 



Input Capacitance 



Output Capacitance 



Plate to Control-Grid Capacitance 



