Rf Tuner, Analysis of 70-220-Mc Amplifiers

circuit. Resistor R224 and capacitor C235

oscillator frequency, which is 10.7 mc

p r o v i d e plate decoupling. The rf output

h i g h e r than the input signal frequency.

v o l t a g e is developed across the parallel-

T h e oscillator is resonated by tuning in-

t u n e d circuit, which consists of tuning

ductor L201D, which is mechanically cou-

inductor L207B, capacitor C236, and coil

p l e d to the inductuner sections that res-

L209. Coil L211 in the plate circuit sup-

onate the first and second rf amplifiers to

p r e s s e s parasitic oscillations. The output

t h e incoming rf signal. Oscillations are

i s coupled to the grid of the second rf

produced in the plate p a r a 1 1 e l-tuned

amplifier V205 by capacitor C237.

c i r c u i t , which consists of tuning inductor

b. Second Rf Amplifier V205. The sig-

L201D, capacitors C224, C225, and C226,

nal voltage from first rf amplifier V204 is

and coil L205. Coils L205 and L206, and

amplified by second rf amplifier V205 and

c a p a c i t o r C226 are made adjustable for

c o u p l e d to the mixer stage V206A. The

t r a c k i n g the oscillator during alignment.

input signal voltage from V204 is developed

F e e d b a c k from. the plate to the grid is

a c r o s s grid resistor R225. Cathode bias

obtained through capacitor C223. Resistor

i s developed by the voltage drop across

R215 is the grid-leak resistor. The cathode

R 2 2 6 , which is bypassed by C213A and

is connected direct to ground. Plate volt-

C 2 1 3 B . Resistor R227 lowers the screen

a g e is applied through voltage-dropping

voltage a n d i s b y p a s s e d b y c a p a c i t o r

r e s i s t o r R216 direct from section W of

C213D. Resistor R228 lowers the Q of the

b a n d selector S201A when this switch is

tuned plate circuit. Resistor R233 and ca-

i n the 20-70 mc position. The oscillator

p a c i t o r C242 provide decoupling for the

output is coupled to the grid of mixer stage

p l a t e circuit. Choke L225 and capacitor

V203A through capacitor C222.

C 2 1 3 C prevent rf currents from circulat-

i n g in the heater circuit. The rf output

37. Rf Tuner, Analysis of 70-220-Mc

v o l t a g e is developed across the parallel-

Amplifiers

t u n e d circuit, which consists of L207C.

(fig. 23)

capacitor C243, and coil L212. Coil L213

W h e n switch S201B is set to the 70-

i n the plate circuit suppresses parasitic

2 2 0 - m c position by rotation of the band

oscillations. The rf output is coupled to the

s e l e c t o r , the signal voltage is coupled to

grid of mixer stage V206A through C244.

f i r s t rf amplifier V204 through rf trans-

former T203. The signal voltage is ampli-

38. Rf Tuner Analysis of 70-220-Mc Mixer

f i e d and coupled to second rf amplifier

and Oscillator

V205.

(fig. 24)

a. First Rf Amplifier V204. The signal

M i x e r s t a g e V 2 0 6 A receives signals

voltage from the main unit enters the

from second rf amplifier V205 and oscil-

tuning unit and is coupled to switch S201B

l a t o r V206B. The oscillator generates a

by a length of coaxial cable. When S201B

frequency that is 10.7 mc higher than the

i s in the 70-220-mc position, the signal

s i g n a l frequency. The two signals are

is applied to rf transformer T203 and

mixed within the tube, whose plate circuit

coupled to the tuned grid circuit of V204.

i s tuned to the difference frequency of

T h i s circuit consists of tuning inductor

10.7 mc.

L207A and capacitor C231. Coil L208 in

a. Mixer V206A. Signal voltages from

t h e grid circuit suppresses parasitic os-

second rf amplifier V205 and from oscil-

cillations. Cathode bias is provided by the

lator V206B are applied to the grid of the

v o l t a g e drop across R221, which is by-

m i x e r . The input voltages are developed

passed by C205A and C205B, Resistor R222

a c r o s s g r i d r e s i s t o r R229. Cathode bias

i s the screen-dropping resistor, bypassed

i s developed b y the voltage drop across

b y c a p a c i t o r C 2 0 5 D . Bypass capacitor

R 2 3 2 , which i s bypassed by C247. Re-

C205C and choke L224 prevent rf currents

s i s t e r R231 i s the screen-dropping re-

from circulating in the heater circuit. Re-

s i s t e r ; it is bypassed by capacitor C246.

sistor R223 lowers the Q of the tuned plate