If. Step Attenuator AT401

output termination of the if. pre-

a center frequency of 42-mc, and a low-

amplifier subassembly. C o a x i a 1

o u t p u t impedance cathode follower, V410

cable assembly W403, with a char-

which supplies driving power to the audio

a c t e r i s t i c impedance of 50 ohms,

a n d meter detectors within detector and

conducts the amplified output sig-

e l e c t r o m e t e r assembly A401.

nal to the input of if. step attenuator

a. Interstate Transformers T405 ( f i g .

AT401.

31). The attenuated if. signal at connector

AT401J2 on the if. step attenuator is con-

47. If. Step Attenuator AT401

ducted through connector plug P412 and a

(fig. 30)

l e n g t h of coaxial cable, to the primary

w i n d i n g of interstage transformer T405.

The output of the 42-mc if. preamplifier

The primary winding has a 50-ohm imped-

i s coupled through connector plugs P409

a n c e . The secondary winding and shunt

a n d P410, part of coaxial cable assembly

c a p a c i t o r C453 resonate together at the

W403, to input jack J1 on the if. step at-

i n t e r m e d i a t e frequency, with R434 func-

tenuator subassembly. This circuit is

tioning as a load resistor. The trans-

i d e n t i c a l and interchangeable with the if.

f o r m e r T405 secondary is connected to

s t e p attenuator previously described for

the grid of third if. amplifier V406.

tuning unit 2 (para 39). The attenuated if.

b. If. Amplifiers V406 through V408.

signal is available at output jack J2 on the

Since the first three if. amplifiers are

i f . step attenuator subassembly for cou-

essentially the same, with identical values

pling through connector plug P412 to the

of circuit elements in their respective

input of the 42-mc if. amplifier subassem-

e l e c t r o d e s , the following circuit descrip-

bly.

t i o n for V406 is also applicable to V407

and V408 (fig. 101). The only difference is

48. If. Amplifier, Detailed Analysis

the use' of a 50-oh.m impedance-matching

(fig. 31 and 32)

transformer at the input to V406.

( 1 ) Cathode bias is developed by the

The 42-mc if. amplifier subassembly

v o l t a g e drop across R435 in the

h o u s e s interstage transformer T405, four

t h i r d if. amplifier (fig. 31). Cap-

amplifiers V406 through V409 operating at

Figure 31. Tuning unit 3, third if. amplifier V406, schematic diagram.