the Form of Free Triode Vibrations. 



207 



incandescent filament before and after the anode circuit 

 was closed. Thus for several triodes of the R type it was 

 found that on closing the anode circuit the current into the 

 positive limb of the filament decreased from if to if— 0*3 4, 

 whilst that from the negative limb increased from if to 

 if+0'1 i a (see fig. 5). If the temperature of the filament is 



Fig. 5. 



fairly high before the anode circuit is closed, as is usually 

 the case in transmitting triode generators, such alterations 

 of heating current may be expected to make marked dif- 

 ferences in temperature and in emission between the two 

 halves of the filament. These alterations in temperature 

 may be noticed visually in the case of a very bright filament, 

 the negative end being made brighter and the positive end 

 dimmed when a large anode current is allowed to flow. 

 The effect on the total emission is difficult to estimate as no 

 accurate data appear to be available for the distribution of 

 temperature along a short filament when a large anode 

 current is flowing. The emission data of Stead * deal with 

 cases in which filament temperatures were not measured 

 while the emitted electrons were actually collected. 



The practical question to be settled is whether in a triode 

 of the ordinary type the emission is increased or decreased 

 when the anode circuit is closed and a thermionic current 

 taken from the tube. We can make an approximate 

 determination of the difference in the energy supplied 

 per second to the filament before and after the electrons 

 are collected. 



* Stead, Journ. I. E. E. vol. lviii. No. 287, Jan. 1020. 



