852 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



to 115 per cent of its normal value. In the thyratron tube rectifiers, the 

 circuit of Fig. 19 operates into a constant resistance load of several 

 megohms. With such a high value of load resistance, the addition of the 

 compounding resistor on the load side of the regulating resistor does not 

 cause appreciable error. In fact, laboratory measurements on an ex- 

 perimental unit show that the compounding can be adjusted to obtain 

 improved regulation of the thyratron tube rectifier when the grid battery 

 eliminator is used in place of the normal grid battery. This is because the 

 grid battery eliminator can be adjusted to over-correct for line voltage 

 variations and thus compensate for the slight amount of residual line 

 regulation error in the thyratron circuit. 



The thermistor in Fig. 19 is a shunt element across one of the resitors 

 in the potentiometer and a change of its resistance is equivalent to chang- 

 ing the potentiometer adjustment. The thermistor decreases its resistance 

 with an increase of ambient temperature so it will change the output 

 voltage when the temperature is changed. This output voltage change is 

 opposed to the voltage changes resulting from the temperature effects 

 in the reference voltage diode and the transistor. By selecting the proper 

 thermistor and the proper ohmic values for the potentiometer resistors, 

 these temperature variations will nearly cancel and the regulated output 

 voltage will be temperature compensated. 



.THYRATRON 



TO OTHER 

 THYRATRON 



REGULATED 

 OUTPUT 



MINUS 1 



Fig. 20 — Grid-battery eliminator for magnitude controlled thyratron rectifier. I 



