THERMIONIC VACUUM TUBES 



69 



frequencies extending from 200 to 3,000 cycles. Receiver shunts are 

 made which, in 10 to 15 steps, will reach a maximum reduction ratio 

 in current of 25:1 which corresponds to an energy reduction of 625:1, 

 and this does not represent the greatest range possible. 



In case a rougher approximation of the amplifying power is suffi- 

 cient, the circuit of Fig. 34a may be simplified by omission of the 

 network R3R4 and reversal of the receiver shunt to present a constant 

 impedance (except for variation of impedance with frequency and 

 phase angle) toward the amplifier. The network R1R2 should prefer- 

 ably be retained and should be so proportioned that the current 

 through the right hand Ri branches is practically the same whether 

 connected with the amplifier or directly to the receiver. 



In measuring the over-all amplification of a multistage circuit, it 

 will probably be desirable to add fixed but known attenuation units 

 similar to R 3 Ri to the receiver shunt which may be cut in or out as 

 required. These units may be given an attenuation equal to and 

 twice the total attenuation of the shunt, etc., after the fashion of the 

 ordinary resistance box. In constructing attenuation networks the 

 arrangement indicated in Fig. 34a will be found desirable in that the 

 symmetrical placing of the branches tends materially to eliminate 

 errors which might otherwise arise due to capacities to ground in the 

 oscillator and amplifier. Pairing of lead wires and shielding of leads 

 and resistance coils will be found desirable for accurate work. 



Fig. 36 



The filter F should be used in case the amplifier tends, because of 

 the limited range of frequencies which it passes or because of some 

 other kind of distortion, to modify the quality of the note given by 



