Circuit Analysis, Static Condition. - TM-11-6625-351-350108

Feedthrough capacitor C518 de-

descriptions. A c o m b i n e d physical-elec-

couples rf currents in the heater

t r i c a l d i a g r a m o f the 400-700-mc tuner

c i r c u i t from the power supply.

(fig. 35) shows that rf amplifier V503 and

o s c i l l a t o r V504 are housed in a chassis

(b) T h e p l a t e c u r r e n t o f t h e t y p e

6299 amplifier tube must be lim-

that contains four tuned coaxial-type cav-

i t e d to a maximum of 10 milli-

i t i e s and one rectangular compartment.

amperes to prolong the life of the

This chassis is also constructed with

c o p l a n a r triode tube. Variable

r e l a t i v e l y thick walls to provide mechan-

r e s i s t o r R508, designated V503

ical stability and electrical isolation. Two

ADJ, is provided for this adjust-

covers (fig. 72) are secured to the chasis.

ment. Rf choke L521 applies the

One is snugly secured to the exterior

+ 1 5 0 - v o l t output of the power

side and provides shielding against rf

supply to one terminal of R508,

leakage for the amplifier cavities and the

which is mounted outside of the

o s c i l l a t o r cavity. A second cover, of Z-

c a v i t y on the tuning unit frame

shape construction, is secured to the com-

a s s e m b 1 y (fig. 72). Capacitor

partment that houses crystal diode CR502

C 5 2 1 penetrates the cavity wall

a n d crystal mixer coil L514. The tuning

a n d connects the B+ potential

slug of the mixer coil projects through a

t h r o u g h voltage-dropping resis-

v e r t i c a l wall of the crystal diode com-

t o r R507 (B, fig. 73) to feed-

p a r t m e n t ; this slug is factory set for a

through capacitor C519, which is

f l a t frequency response over the band.

mounted on a supporting bracket

R e f e r e n c e to the parts location diagram

( A , fig. 73) in the plate cavity.

( f i g . 73) shows that five feedthrough ca-

The bracket serves as a con-

p a c i t o r s (C517, C521, C526, C527, and

v e n i e n t anchoring point for one

C528), a right-angle input signal connector

terminal of rf choke L513, which

(J508), and a termination (CP502) for the

i s wound on R506. The second

o u t p u t signal cable are inserted through

terminal of rf choke L513 is

t h e tuner walls for purposes described in

b below.

soldered to the underside of the

b. Circuit Analysis, Static Condition.

metallic tube clip which supports

The 400-700-mc rf tuner consists of five

a m p l i f i e r tube V503 within the

s e p a r a t e l y confined but functionally in-

c a v i t y . Rf choke L513 connects

t e r r e l a t e d circuits with operating voltages

the B+ potential to the plate elec-

for the tube electrodes applied as follows:

trode of V503 and offers a high

(1) Amplifier circuit. Similar to the

i m p e d a n c e to rf currents in the

7 0 0 - 1 , 0 0 0 - m c tuner (para 51b(1)),

p l a t e circuit. Capacitor C513, of

the amplifier circuit uses a

tubular construction, is also sol-

g r o u n d e d-grid coplanar triode,

dered to the underside of the

V503 (fig. 35 and 73). The grid disk

plate tube clip, and offers a low-

is secured to the grounded partition

i m p e d a n c e path for rf energy to

t h a t separates the cathode input

p a s s to the tuned plate output

cavity from the plate output cavity;

cavity.

this avoids the need for neutraliza-

(2) Oscillator circuit. The oscillator

t i o n of the amplifier input circuit

c o n s i s t s of a miniature-type 6T4

a n d minimizes the generation of

t r i o d e connected to two parallel

s p u r i o u s frequencies.

1/2-wavelength c a p a c i t y-loaded

transmission lines (A, fig. 73). The

(a) Heater voltage is connected from

length of the parallel transmission

t h e power supply, through feed-

t h r o u g h capacitor C517 (B, fig.

l i n e s must be greater than those

73) and rf choke L512, to one of

i n the 700-1,000-mc tuner so that

t h e heater pins. The return path

resonance can be obtained over

for the heater voltage is through

t h e 400-700-mc tuning range. For

t h i s r e a s o n , t h e large-envelope

rf choke L511 to chassis ground.