766 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



pedance values are 800 ohms negative resistance and 50 ohms inductive 

 reactance at 10 milliamperes operating current, with a superimposed 

 audio-frequency signal of 3,000 cycles per second. 



Even though the cathode geometry is stable, some cathode material 

 escapes through the orifice and will rapidly collect on an anode placed 

 directly over the opening. It is therefore necessary to locate the anode 

 to one side of the orifice. The extremely high ionization density near the 

 cathode orifice allows considerable flexibility in anode location without 

 affecting the sustaining voltage or destroying the negative resistance. 



High switching-voltage gain is obtained by using a small anode formed 

 by a 0.005-inch diameter molybdenum wire placed perpendicular to the 

 end of the cathode at a spacing of approximately 0.005 inch. Breakdown 

 voltage is nominally 190 volts with a range of ±10 volts over all tubes 

 and over the nominal operating life of 4,000 hours. The sustaining volt- 



GETTER FLASH — _ 



SPRING CONTACT 



BARIUM GETTER 



BULB- 



ANODE 

 CATHODE 



SHIELD FOR 

 SPUTTER PROTECTION 



Fig. 5 — A talking-path switching diode. 



