Rf Tuner, 400-700 Mc, Dynamic Circuit Analysis

cavity and serves as an rf bypass.

acorn-type electron tube cannot be

The B+ voltage is applied through

u t i l i z e d , and a smaller envelope-

rf choke L518 to the plate (pins

type 6T4 tube is employed. Oper-

1 and 7) of the oscillator tube

ating potentials are applied to the

and to one of the l/2-wavelength

t e r m i n a l s at the base of the tube

parallel transmission lines in

socket as follows:

t h e oscillator plate circuit. The

(a) Heater voltage is connected from

second parallel transmission line

t h e power supply through feed-

o p e r a t e s at dc ground potential.

t h r o u g h capacitor C528 (A, fig.

7 3 ) which penetrates the oscil-

l a t o r compartment. Bypass ca-

54. Rf Tuner, 400-700 Mc, Dynamic

pacitor C529 decouples rf energy

Circuit Analysis

i n the heater circuit from the

(fig. 35)

heater power supply line. A short

T h e dynamic circuit analysis for the

length of wire connects the heater

400-700-mc rf tuner is identical with that

v o l t a g e through rf choke L516

for the 700-1,000-mc tuner (para 52)

to one side of V504 heater (pin 4).

except for substitution of applicable refer-

The heater voltage return path is

e n c e symbols and the following circuit

through rf choke L515 to chassis

components:

ground.

a. V503 Input Circuit. No pickup loop is

(b) G r i d bias for oscillator V504 is

employed for coupling the rf energy from

d e v e l o p e d by the voltage drop

the first to the second coaxial-type tuned

a c r o s s grid resistor R509. The

cavity. Because a pickup loop at the lower

c a t h o d e (pin 5) is connected

f r e q u e n c y range of 400- to 700-mc must

through rf choke L517 to chassis

be considerably longer than that employed

ground.

in the upper frequency band (700-to 1,000-

(c) The 105-volt dc potential is ap-

mc), undesirable resonances in the tuning

plied to the plate (pins 1 and 7)

range can be created. Instead of a pickup

of the oscillator tube only w h e n

loop, an aperture of proper dimensions for

the front panel band selector

the pass band of the frequencies desired is

(S503) is rotated to the 400-700 -

c u t into the wall separating the first and

mc position. The dc potential is

second input tuned cavities. This aperture

a p p l i e d through two rf chokes,

method of coupling permits ample transfer

t w o feedthrough capacitors, and

of rf energy from the first to the second

one resistor. The first choke,

input cavity. Except for the difference in

L519, is outside of the rf tuner

coupling methods, V503 amplifier employs

and in series with terminal 2 on

b a n d selector S503 (front sec-

reference symbol C520 as the ganged

tion) which applies B+ potential

t u n i n g capacitor. Metallic tab capacitors

t o V504. Feedthrough capacitor

C580 and C590 permit vernier tracking of

C527 penetrates the c h a s s is;

the amplifier and oscillator sections of the

h o w e v e r , this capacitor serves

t u n i n g capacitor.

only as a convenient tie point for

b. V503 Output Circuit. Section C of

t u n i n g capacitor C520 loads the single-

a n c h o r i n g one terminal of cur-

tuned coaxial line in the amplifier output

rent-limiting resistor R511 to

circuit. Metallic tab capacitor C600 serves

t h e exterior of the chassis (A,

f i g . 73). The B+ voltage is de-

the same function as metallic tab capac-

itor C570 for the 700-1,000-mc rf ampli-

creased by fixed resistor R511 to

fier.

the proper value for tube opera-

t i o n . The low-potential side of

c. V504 Oscillator Circuit. Section D of

tuning c a p a c i t o r C250, mechanically

R511 is connected to feedthrough

ganged with amplifier sections A, B, and

c a p a c i t o r C526 which penetrates

C of C520, provides the tracking frequency

the exterior wail of the oscillator