HIGH i-i<r.Qi'nxcy .iMruriiiRs 



191 



It is seen that the .impliru.itinii (-iir\e C for a step-uji ratio of 1:1 

 is extremely tlat as compared with the ainpliliratioii ciirxe shown in 

 Fig. o for a choke roil working at SoO kilocycles. 



In connection with these experiments with tuned circuits and 

 choke coils it may be mentioned that in order to .separate the DC 

 plate voltage from the PC grid voltage, it will often he found of afl- 



Fig. 7 — Curve Showing the Effect of Ratio of Transformation in the Characteristic 

 of a Choke Coil Coupled .\niplifiir 



vantage to replace the coil by a transformer wiiii \er\- close coupling- 

 In all our experiments, we have found that the amplification curves 

 obtained in the two cases are identical when the cou()ling coefficient 

 for the two windings of the transformer is nearK- unity. 



LOOSEl-Y COLPI.ED Tr.\nsfor.mer Ami'likier 



From the amplification curves obtained with choke coils, it will be 

 seen that the frequency range obtainable with a choke coil amplifier 

 is not as wide as might be desirable in some cases. This is especially 

 true for higher frequencies between 300,000 and 1,000,000 cycles, and 

 where a wide frequency band is desired these choke coils have, there- 

 fore, been replaced by transformers with a rather loose coupling, in 

 which case the transformers will have the characteristics of two 

 ordinary coupled circuits and give an amplification curve with two 

 peaks. 



It has been found by experiment that such transformers can actually 

 be treated just as ordinary coupled circuits arul the amplification 



