Circuit Analysis, Static Condition. - TM-11-6625-351-350103

p i n s . The return path for heater

with relatively thick walls to provide a high

voltage is through rf choke L501

d e g r e e of mechanical stability and elec-

to chassis ground. Chokes L501,

trical isolation. Three covers (fig. 72) are

L 5 0 2 , and two decoupling net-

s e c u r e d to the chassis; one cover is se-

works (consisting of choke L524-

c u r e d to the side of the chassis, and a

bypass capacitor C531 and choke

second cover is secured to the end of the

L545-b y p a s s capacitor C530,

tuner housing the variable capacitor plates.

T h e s e two covers provide proper shield-

s h o w n on the overall schematic

d i a g r a m (fig. 102)), effectively

i n g against rf leakage for the amplifier

p r e v e n t rf currents from circu-

c a v i t i e s , the oscillator cavity, and the

compartment that houses voltage-dropping

lating in the heater supply.

r e s i s t o r R505 in the oscillator plate cir-

(b) S i n c e the plate current of the

c u i t . The third cover is secured to the

type 6299 tube must be limited to

compartment that houses crystal diode

a maximum of 10 milliamperes,

C R 5 0 1 and crystal mixer coil L505. An

V 5 0 1 ADJ control (fig. 34) is

access hole is provided at the top of the

provided for making adjustments.

cover to permit factory adjustment of the

R f choke L521 applies the 150-

tuning shaft for a flat frequency response

volt output of the power supply to

over the band. Reference to the parts loca-

one terminal of variable resistor

tion diagram (fig. 74) shows that four feed-

R 5 0 3 , which is mounted on the

through capacitors (C502, C505, C540, and

tuning unit frame assembly (fig.

7 4 ) . The variable arm of R503

C511), a right-angle input signal connector

i s in series with choke L504 to

(J506), and a termination (CP501) are in-

feedthrough c a p a c i t o r C505,

s e r t e d through the chassis walls for pur-

which penetrates the cavity wall

poses described in b b e l o w .

and connects the B+ potential to

b . Circuit Analysis, Static Condition.

the compartment that houses the

The rf tuner consists of six separately

c r y s t a l diode. A wire lead con-

c o n f i n e d but functionally interrelated cir-

nects C505 to the junction of R502

cuits, with operating voltages for the tube

and feedthrough capacitor C504.

e l e c t r o d e s applied as described below:

(1) Amplifier circuit. T h e a m p l i f i e r

T h i s capacitor serves only as a

convenient tie point for anchoring

c i r c u i t uses a grounded-grid co-

p l a n a r triode, V501 (A, fig. 74),

one terminal of R502. Because of

the voltage drop across R502, a

w h i c h is secured to the partition

lower value of B+ potential is ap-

t h a t separates the cathode cavity

plied through feedthrough capac-

f r o m the plate cavity. A screw is

itor C503 to the plate of V501. Rf

u s e d to transfer spring pressure

f r o m a metallic clamp to the grid

choke L503 wound on R501, pre-

disk of the electron tube; this as-

sents a high impedance to rf cur-

s u r e s a secure electrical contact.

rents entering the B+ power sup-

Since the clamp, the partition, and

ply line.

(2) Oscillator circuit. The oscillator

t h e electron tube grid are always

at rf ground potential, the need for

c i r c u i t uses an acorn-type triode

neutralization of the amplifier input

( V 5 0 2 ) which is mounted by its

circuit is avoided. Simultaneously,

radiating pins to supporting struc-

the possible generation of spurious

t u r e s within the oscillator cavity

and undersided frequencies is kept

(A, fig. 74). The plate (pins 3 and

to a minimum.

4) is secured to an adjustment nut

which is anchored to one of the two

(a) Heater voltage (6.3 volts) ac is

p a r a l l e l l/2-wavelength capacity-

connected from the power supply

l o a d e d transmission lines in the

through rf choke L509, feed-

t h r o u g h capacitor C502, and rf

cavity. The grid (pins 3 and 5) is

secured to a second adjustment nut

choke L502 to one of the heater