VACUUM TUBES AS HIGH-FREQUENCY OSCILLATORS 133 



tion. However, conventional screen-grid tetrodes and pentodes are 

 available which function satisfactorily over the major portion of the 

 frequency range covered by the conventional 3-element tube as an 

 oscillator. 



For frequencies above approximately 60 megacycles specially de- 

 signed tubes are required. Because of the similarity in the special 

 frequency requirements, it is expected that there will be found a 

 succession of multi-element tubes for amplification use, each rated for 

 a band of frequencies, patterned after corresponding triode oscillators. 

 The special frequency requirements for the amplifying tube are even 

 more severe than those for the triode oscillator, so that the multi- 

 element amplifying tube will in general cease amplifying at a frequency 

 somewhat lower than the frequency limit of oscillation of the corre- 

 sponding triode oscillator. 



Thompson and Rose * have described small screen-grid tubes which 

 will amplify at frequencies of 300 to 400 megacycles. One of these 

 tubes is shown in Fig. 13. Their characteristics are similar to those 

 of the conventional screen-grid tube in many respects. The very 

 great reductions in inter-electrode capacitances, lead inductances, and 

 transit time make possible the construction of receiving circuits using 

 tuned radio frequency amplification at these very high frequencies. 

 The ratio of the frequency limits of the corresponding triode as an 

 oscillator (1000 megacycles) to the frequency at which amplification 

 was reported (400 megacycles) is typical and illustrates the apparently 

 inevitable failure of the amplifier to keep pace with the oscillator in 

 the struggle toward higher and higher frequencies. 



References 

 Negative Grid Tubes 



1. E. P. McArthur and E. E. Spitzer, "Vacuum Tubes as High-Frequency Oscil- 



lators," /. R. E. Proc, V. 19, 1931, p. 1971. (Bibliography of 28 titles.) 



2. C. E. Fay and A. L. Samuel, "Vacuum Tubes for Generating Frequencies Above 



100 Megacycles," I. R. E. Proc, v. 22, 1934, p. 679. 



3. B. J. Thompson and G. M. Rose, "Vacuum Tubes of Small Dimensions for Use 



at Extremely High Frequencies," /. R. E. Proc, v. 21, 1933, p. 1707. 



4. W. H. Wenstrom, "An Experimental Study of Regenerative Ultra-Short Wave 



Oscillators," I. R. E. Proc, v. 20, 1932, p. 113. 



5. I. E. Mouromtseff and H. V. Noble, "A New Type of Ultra-Short Wave Oscil- 



lator," /. R. E. Proc, v. 20, 1932, p. 1328. 



6. W. Kroebel, "On the Production of Undamped Oscillations of Wave-Lengths of 



the Order of a Decimeter in a Reaction Circuit I," Ann. der Physik, Series 5, 

 v. 14, 1932, p. 80. 



Positive Grid Tubes 



7. H. Barkhausen and K. Kurz, "The Shortest Waves Obtainable with Vacuum 



Tubes," Phys. Zeits., v. 21, 1920, p. 1. 



8. E. W. B. Gill and J. H. Morrell, "Short Electric Waves Obtained by Valves," 



Phil. Mag., V. 44, 1922, p. 161. 



