264 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



pulse of variable width (within limits) on the input. Normally the emitter 

 is held slightly negative with respect to the base. The potential difference 

 determines the sensitivity of the amplifier. When a positive input pulse 

 is received, the emitter diode conducts causing an increase in collector 

 current. The change in bias of the diode in the emitter circuit permits 

 it to conduct and charge the condenser. With the removal of the input 

 pulse the discharge of the condenser holds the transistor pair on. The 

 time constant of the circuit determines the on time. When the emitter 

 potential falls below the base potential, the transistor pair is turned off. 



The amplifiers and bi-stable circuits or flip-flops, >as they are called 

 more frequently, are mounted together in plug-in packages. Each pack- 

 age contains 8 basic circuits divided 7-1, 6-2, or 2-6, between amplifiers 

 and fhp-flops. Fig. 2(c) shows one of these packages. They are smaller 

 than the gate or line unit packages, having only 28 terminals instead of 

 42. 



The transistors for the field trial model w^ere plugged into small hear- 

 ing aid sockets mounted on the printed wiring boards. For a production 

 model it w^ould be expected that the transistors w^ould be soldered in. 



d. Transistor Ring Counter 



By combining bi-stable transistor and diode pulse gate circuits to- 

 gether in the manner shown in Fig. 12 a ring counter may be made, with 



INPUT 



p-n-p 



^w 



^vW-" 



I 



+ 5V 



OUTPUT 



-16 V 



INPUT 



OUTPUT 



Fig. 11 — Transistor pulse amplifier. 



