the Form of Free Triode Vibrations. 



217 



is as large as this, since no account has been taken of the 

 alteration (decrease) in resistance of the filament due to 

 the general cooling when the anode circuit is completed. 

 Thus we really ought to compare the distribution of the 

 emission current through the two halves of the filament not 

 with ?o (the heating current before the electrons are collected) 

 but with £(/, the heating current which would flow if by some 

 means the cooling effect of evaporation was experienced as 

 well as the Joulean effect of the emission current, but 

 without the emission current actually flowing through the 

 filament again. It is obvious, since the filament is cooled 

 as a whole when electrons are collected, that i Q ' = i -\- A, 

 where A is a positive quantity. Thus we may write the 

 currents in the two limbs of the filament as 



*+=«o / -'{A + 0-3(ii + t 1 )}: and tl = t / +(0-7)«i + t 8 ) — A}. 



. . . (12) 



The exact value of A is of course unknown, but (12) at 

 once shows that the actual distribution of the emission is not 

 as unequal as (11) would lead one to expect *. * 



It is thus seen that in the case of a triode filament of 

 ordinary size with small series resistance the matter is some- 

 what complicated, since the re>istance of the filament is 

 decreased due to cooling and the anode current is divided 



Fist 11. 



Ill B 



-S- 32 Vott 



ia) 



L^A/VVV^VVJ 



unequally between the two halves of the filament, 

 adopting a somewhat artificial heating circuit with 1 

 series resistance, both of these effects may be brought u 

 control and the simple thermal effect of the anode em 

 studied. Fig. 11 shows the actual circuit used. 



* Actual experiments carried out using 1 a divided anode have s 

 that for ordinary R type triodes the emission from the negative h 

 the filament is about 1 5 times that from the positive half. 



Phil. Mag. S. 6. Vol. 42. No. 248. Aug. 1921. Q 



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