THE L3 SYSTEM — AMPLIFIERS 913 



be appreciable at +14 dbm of any single frequency. At +18 dbm the 

 dc effects of overload show up as slight changes in the transmission of 

 the pilot frequencies. At +26 dbm, the second order modulation is 

 3 db, the third order modulation is 6 db, higher per line amplifier than 

 would be predicted from small signal behaviour. 



Flat Amplifier 



The fiat gain amplifier, which is used as a transmitting amplifier and 

 to make up for equalizer loss at various points in the system, is basically 

 the same as the line amplifier, with only the obviously necessary modifica- 

 tions. The input beta circuit is nearly flat, the regulating network has 

 been replaced by a fixed gain network which contains a single variable 

 element whose adjustment at the factory compensates to some extent for 

 variations in the coupling networks, and the input coupling network 

 has been modified so that the peaking used in the line amplifier is re- 

 placed by a drop in the high-frequency gain of this network. The output 

 beta circuit has been modified to give flat gain control of ±1.0 db in 

 0.2 db steps. The interstage designs are changed to readjust the feedback 

 so that the modulation suppression and the change in gain as tubes 

 age will be nearly the same as in the line amplifier. Somewhat more 

 feedback is obtained in the output amplifier since no network is needed 

 in the output amplifier interstage to adjust the 30-mc phase for an 

 unfavorable regulating network setting. 



The nominal gain of the flat gain amplifier has been set at 34 db and 

 is flat to within ±0.2 db over the transmitted band. The amplifier circuit 

 capacities are low enough so that the inter-amplifier network could be 

 built to give considerably more gain than this; the limit has been set 

 so that flat gain amplifier noise contributions to the complete system 

 noise will not exceed about 1.0 db at the television carrier. 



Acknowledgements 



As in any corporate development, many members of the Laboratories 

 have made important contributions to the L3 amplifier design. Particular 

 mention should be made of the work of S. E. Miller on fundamental 

 ampfifier design, S. Darlington and T. R. Finch on network design, 

 C. W. Thulin on the precision transformer, B. J. Kinsburg on quaUty 

 control problems, E. Ley on mechanical design, and E. F. O'Neill on the 

 flat gain ampfifier and on high-frequency stability problems in both 

 amplifiers. 



