592 BELL SYSTEM TECHNICAL JOURNAL 



studies. It requires considerable apparatus and is slow in operation. 

 The fall of gain method while it gives approximately the same results 

 as the other methods is not so precise since the gain falls very slowly 

 at the overload point and does not begin to fall rapidly till the ampli- 

 fier is heavily overloaded. It is therefore, difficult to pick the exact 

 point where overloading occurs. Moreover the method affords no 

 indication of the kind of overloading that is occurring. 



Determination by the use of the cathode ray oscillograph is more 

 rapid and in most cases more precise although in the case of push-pull 

 amplifiers with low grid-circuit impedances the overload point is 

 not so clearly marked as in the other cases. The shape of the curves 

 affords valuable information as to the place in the circuit where the 

 overloading occurs and, by comparison with previously made analyses, 

 a good indication of the amount of harmonic introduced. It there- 

 fore forms a very valuable tool for the design engineer. 



By either method the result obtained shows the load carrying 

 capacity of an amplifier for a single frequency. The complete answer 

 as to how much volume in speech or music a particular amplifying 

 system will handle depends upon an analysis of the power in the 

 speech or music such as that given in C. F. Sacia's paper on Speech 

 Power and Energy in the October, 1925, issue of this Journal. 



BIBLIOGRPAHY 



1. "Physical Measurements of Audition and Their Bearing on the Theory of 

 Hearing," Harvey, Fletcher, Bell System Technical Journal, Oct., 1923, Vol. H, p. 145. 



2. "Speech Power and Energy," C. F. Sacia, Bell System Technical Journal, Oct., 

 1925, Vol. IV, p. 627. 



3. "A Theoretical Study of the Three-Element Vacuum Tube," John R. Carson, 

 Proceedings I. R. E., Vol. VH, No. 2. 



4. "Operation of Thermionic Vacuum Tube Circuits," F. B. Llewellyn, Bell 

 System Technical Journal, July, 1926, Vol. V, p. 433. 



5. "Design of Non-Distorting Power Amplifiers," E. W. Kellogg, Journal A. I. 

 E. E., May, 1925, Vol. 44, p. 490. 



6. "The Performance of Amplifiers," H. A. Thomas, Journal L E. E. (London), 

 Feb., 1926, Vol. 64, p. 253. 



7. "Selecting an Audio-Frequency Amplifier," D. F. Whiting, Bell Laboratories 

 Record, June, 1926. 



