ULTRA-HIGH-FREQUENCY POWER AMPLIFIER 



33 



The oscillators are push-pull tuned-plate — tuned-grid oscillators 

 employing Western Electric type 304-A tubes with about 900 volts on 

 their plates. These oscillators each deliver about twenty-five watts 

 of radio-frequency power, nearly all of which is dissipated in a resist- 

 ance load inside the shielding compartments. The receiver (voltage 

 analyzer) has approximately one hundred decibels gain and a ninety- 

 three-decibel attenuator adjustable in one-decibel steps so that 

 measurements over a very wide range of amplitudes are possible. It 

 was found desirable to interpose an additional amplifier (also using 

 these push-pull pentodes) between the output of the bridge and the 

 tube and circuits under test. Of course this amplifier introduces a 

 possible source of distortion ahead of the circuit under test and care 

 must be taken to operate it under such conditions that an adequate 

 margin exists between distortion level measured at its output and 

 distortion level existing at the output of the tube under test. 



In Table IV are shown the results of distortion measurements made 

 under several typical sets of operating conditions. 



TABLE IV 



Ratio of Amplitude of Third Order Modulation Products to Amplitude 

 OF One of Two Equal Test Frequencies 



Frequency = 80 megacycles 



* For single frequency whose amplitude is the sum of the amplitudes of the two 

 test frequencies. 



Other Applications 



A study of the performance of these tubes as class B amplifiers, as 

 narmonic generators, and as modulators apparently presents no serious 

 additional problems and requires very little in the way of additional 

 new technique. Tests indicate that in the neighborhood of 150 mega- 

 cycles the performance of these tubes in such modes of operation is 

 comparable to that of conventional pentodes in the ordinary short- 

 wave range. In a two-stage amplifier using these tubes, with the first 



