If. Amplifier Alignment, Tuning Unit 4, General

plastic alignment tool with internal dimens-

95. If. Amplifier Alignment, Tuning

i o n s for fitting l/4-inch hexagonal nuts,

Unit 4, General

as was used for the previous tuning units.

a. The alignment of the tuning unit 4 if.

The following chart indicates the location

amplifier is similar to that of tuning unit

of the if. alignment adjustments.

3 (para 92). To align the 42-mc if. ampli-

f i e r subassembly (housing stages V508

through V512) and the 42-mc if. preampli-

f i e r subassembly (housing stages V505

through V507), remove the main unit from

i t s instrument case (para 40b, item 12,

T M 11-6625-351-12). Remove the dust

c o v e r from tuning unit 3. Interconnect

tuning unit 3 to the main unit with the test

harness (fig. 46).

b. Inject the unmodulated output of the

tuning unit 3 signal generator into the if.

preamplifier as indicated in the test setup

(fig. 91).

Set the front-panel controls on the

(1) Connect one end of Cord CG-55B/U

test

set as listed in para 88c, except for

supplied with the tuning unit 3 sig-

the

FREQUENCY RANGE-MC switch; set

n a l generator into the generator

this

switch to the 400-700-mc position.

front-panel C A R R I E R OUTPUT

jack. This cord is terminated with

96. Alignment of 42-Mc If. Amplifiers,

a Radio Frequency Plug UG-

Tuning Unit 4

21B/U at each end.

(fig. 72)

(2) U s e the same cable assembly that

was fabricated for aligning the if.

a. Set the frequency dial of the tuning

amplifier of t u n i n g unit 2 (para

unit 3 signal generator to 42 mc and inject

89a(2) and (3)).

the unmodulated output signal into the if.

(3) Disconnect plug P509 (on the input

p r e a m p l i f i e r jack, J509. This jack is

cable assembly at the top of the if.

located on the electron tube side of the sub-

p r e a m p l i f i e r ) from its mating jack

assembly.

J509 (fig. 72).

Note: Do not confuse input jack J509 with input

(4) Connect the output of the tuning unit

jack J507, which is located at the end of the if.

p r e a m p l i f i e r adjacent to the gear train assembly.

3 signal generator, through the fab-

With the FREQUENCY RANGE-MC switch rotated

ricated cable assembly ((2) above),

to the 400-700-mc position m i c r o s w i t c h S502,

to jack J509 on the top of the if.

creates a path of continuity from inputjack J509 to

preamplifier.

if. transformer T501. Simultaneously, an open cir-

cuit exists at input jack J507 S o that the output of

Note: T h r o u g h o u t the following align-

only the 400-700-mc. tuner can be applied to the if.

ment procedure, d e c r e a s e the tuning unit

preamplifier circuit.

3 signal generator MICROVOLTS output

b. Set the MICROVOLTS control of the

control and the tuning unit GAIN control

s i g n a l generator to produce an approxi-

(if necessary) so that the main unit panel

meter maintains an onscale indication. Ini-

mate midscale indication on the main unit

tially set the tuning unit 3 signal genera-

p a n e l meter,

t o r MICROVOLTS control to a value of

c. The 42-mc if. amplifier is mounted

20K (equivalent to -20 dbm); then reduce

in a horizontal position at the top of the

the output setting as required, to keep the

p a n e l m e t e r i n d i c a t i o n lower than full

t u n i n g unit. W o r k i n g from the electron

seal e.

tube side of the 42-mc if. amplifier sub-

a s s e m b l y , adjust the cores of networks

c. As in tuning units 1, 2, and 3, the

Z503, T506, T505, T504, and T503, in this

cores of the tuned networks on the if. pre-

sequence, to obtain a maximum panel

amplifier and amplifier subassemblies are

m e t e r indication. A s the 42-mc unit is

provided with hexagonal nuts. Use the same

208