THE L3 SYSTEM — DESIGN 813 



at low frequencies where it is difficult and expensive to design power 

 separation filters to meet the system requirements. 



The dc plate and bias supply voltages for amplifiers and regulators 

 could be obtained by conventional rectifier circuits except for one com- 

 plication which such arrangements introduce. This complication is the 

 fact that a rectifier terminated in a low-pass filter (conventional ripple 

 filter) reflects a highly distorted current wave into the primary circuit. 

 If the primary current is so distorted the various power supphes in the 

 series circuit will be fed with other than a sine wave of current and will 

 supply different voltages depending on the wave form. Since the heater 

 power depends on the rms value of current while the dc output depends 

 on the peak value of voltage, it is easily seen that the relationship be- 

 tween these two will change with the wave form of the applied current. 

 Furthermore, the line loading to be discussed later must be calculated 

 on the basis of a pure sine wave; appreciable harmonics in the line cur- 

 rent tend to make it impossible to predetermine the loading to any reason- 

 able degree of accuracy. 



It was found that these problems could be avoided and the power 

 factor of the power supply made very nearly unity if the rectifier (rect 

 i) was terminated in a constant resistance load rather than a low-pass 

 filter. This was provided by paralleling the conventional low-pass filter 

 with a high-pass section terminated in the proper resistance load. To 

 avoid wasting the power in this load a second rectifier was added (rect 

 2) . The dc output of this circuit is used in series with the main dc supply 

 to provide the higher voltage required for the output stage of the am- 

 plifier. This rectifier must also be terminated resistively although its 

 effect on the main current wave is less than that of the first rectifier, and 

 the power dissipated is smaller. Since there was a further use for a small 

 amount of power for bias in the regulators, rect 3 was added to produce 

 a regulated voltage in conjunction with a conventional gas tube circuit. 

 This rectifier and its load provide the termination for the high pass 

 section of the filter circuit for rect 2. A second gas tube circuit is used 

 to obtain a regulated bias supply for amplifiers and regulators from the 

 3 15- volt source. The loads on both gas tube circuits are fixed so regula- 

 tion for variation in input voltage only is required. For this reason a 

 low current, highly stable gas tube could be used. 



3.23 Power Loading 



The power transmission circuit of a power loop is essentially a re- 

 sistance-capacity network at the power frequency. The line and the 



