TRANSFORMER COUPLING CIRCUITS 



617 



efficiently transmitted the internal plate voltage of the first tube to 

 the grid circuit of the second tube. The internal plate impedance of 

 the particular tube used was approximately 400,000 ohms. A two- 

 stage amplifier consisting of two shielded-grid amplifying tubes and 

 two transformer coupling circuits connected in cascade gave a voltage 

 amplification of approximately 40,000 times over the frequency band 

 shown. 



Another type of transformer coupling circuit which was employed 

 in the intermediate frequency amplifier of a high quality superhetero- 

 dyne radio receiver is shown in ¥\g. 5. The circuit schematic of this 



Fig. 5 — Coupling circuit consisting of two-tuned transformers connected in cascade. 



transformer and its transmission characteristic are shown in Fig. 6. 

 It will be noted that two transformers are mounted separately and 

 electrically connected by a series condenser d' . C\ and Li were 



determined from equations (8) and (9) and Li = L2 = L3. C2 = — ■ 



The capacitance across L4 was equal to the winding capacity and 

 effective input capacity of the second tube. The second tube of 

 Fig. 6 was the second detector of the intermediate frequency amplifier. 

 The elements of a coupling circuit consisting of three transformers 

 and their associated condensers for operation over the carrier frequency 

 range of 50 to 150 kilocycles are shown in Fig. 7. The windings of 

 stranded wire are applied in narrow grooves to reduce the dielectric 

 losses of the insulation between layers. The ratio of the reactance to 

 the effective resistance for these coils varies from approximately 150 

 at 50 kilocycles to approximately 240 at 150 kilocycles. The halves 

 of the winding connected to the grid circuit of the balanced tubes 



