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BELL SYSTEM TECHNICAL JOURNAL 



is a direct indication of signal strength, displayed as a function of fre- 

 quency. 



The results reported here were obtained using the BTL 1553 tube, 

 which is a laboratory model. Samples of the production model. Western 

 Electric 416A, have also been used in this oscillator with quite similar 

 results. To adapt the oscillator for the 416A, the grid ring should be 

 threaded on the inside to fit the threads on the grid disk of that tube. 



4. An Equivalent Circuit 



The tield configuration in the cavity of the oscillator is quite complex, 

 and cannot be readily described in any quantitative fashion. The formu- 

 lation of an equivalent circuit would require many approximations and 



Fig. 5. — The complete oscillator, showing the sweeping mechanism partially dis- 

 mantled. 



judicious guesses if values are to be specified for the various circuit 

 parameters. The circuit of Fig. 3 is believed to be equivalent in a qualita- 

 tive sense. 



A portion of the circuit is within the tube itself. This is the region en- 

 closed by the dotted line in T^ig. 3. The T of elements which include I'n, 

 Cyp, nCgp and the injected currents, is the equivalent circuit of Llewellyn 

 and Peterson^ for the active region of a triode. Exj)erimentally deter- 

 mined values for these quantities are reported by Robertson'-. I'u is the 

 admittance of an equivalent diode between the grid and cathode, and the 

 injected currents indicated by the arrows are the electronic transfer cur- 

 rents associated with the grid voltage and the transadmittance. At high 



' Llewellyn and Peterson, "Vacuum Tube Networks," LR.E. Proc, Vol. i2, pp. 144- 

 166 (.March 1944). 



2 S. D. Robertson, "Electronic Admittances of Parallel-Plane Electron Tubes at 4000 

 •Megacycles," B. S. T. J., Vol. 28, p. 619, Oct. 1949. 



