DESIGN FACTORS OF THE 1553 TRIODE 513 



width is a constant, a figure of merit. The derivation is outlined in 

 Appendix 1. 



47rCout 



The numerator here is just the square of the maximum ac current; that 

 is, the dc current /20 , multiphed by a factor F{C) depending on the allow- 

 able compression C, and by the gap coupling coeflftcient F2(02) of the elec- 

 tron stream to the output gap. The latter is of course a function of the 

 output transit angle 6-2. . It is assumed that the load is a matched simple 

 resonant circuit and the band is taken 3 db down. 



The power optimum must clearly be somewhat different from the gain 

 optimum previously discussed. For example, the transadmittance does not 

 appear here, nor does any property of the input circuit; while the magni- 

 tude of the direct electron current, which did not appear in the gain- 

 band product, is now important. The capacitance of the output circuit 

 appears in both figures of merit. 



In terms of internal parameters of the tube, application of Llewellyn 

 and Peterson's theory along the lines previously discussed leads to the 

 following expression for power-band product: 



Mi (P) = K[Af r~(C)] [02 Fl (62) VVJ (7) 



where A is the electrode area, F^{C) is a function of the allowable dis- 

 tortion limits, K is a, constant which may depend upon frequency, and 

 the other symbols are as before. 



Considering first the dependence on output transit angle and plate 

 voltage, one sees that this figure of merit has exactly the same form as 

 the gain-band product. It is, however, not quite safe to assume therefore 

 that exactly the same output configuration is still optimum, because the 

 factors entering into the choice of output spacing have not exactly the 

 same relative importance any longer; for example, a positive grid may be 

 less objectionable, or a higher plate voltage may be permissible. Still, as a 

 first approximation one may assume the output configuration to be al- 

 ready somewhere near optimum. 



Other factors of the power-band figure of merit show considerable 

 difference from the gain-band product. For instance, the electrode area 

 enters the picture explicitly, suggesting that a larger area tube would 

 give more power. The current density enters squared instead of only to 

 the § power; the explicit dependence on input spacing is missing. The 

 compression function F(C) depends mostly on the input conditions in a 

 complicated way difficult to calculate. It can be approximated graphically 

 from static characteristics. 



