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-o

Block

diagram,

record

circuit

8-3

89-0144

Issue

A

RECORD

AMPLIFIER

The

record

section

of

the

electronic

assembly

is

a

fori)

’

stage,

high

gain,

resistance

coupled

amplifier

using

transformer

coupling

for

micro



phone

or

balanced

bridge

inputs,

and

by-pass



ing

the

transformer

and

the

first

stage

when

unbalanced

bridge

input

is

selected.

Two

dual

triodes,

1V1

and

lV2and

their

related

circuitry,

form

the

four

stages

of

amplification.

When

the

microphone

INPUT

is

selected

the

signal

from

5J1

is

impressed

across

the

primary

of

input

transformer

6T1

and

de



livered

through

the

secondary

to

the

grid

of

IV

1.

In

the

balanced

bridge

arrangement,

the

signal

passes

through

resistor

network

4R1,

4R4

and

4R5

to

input

transformer

6T1

with

resistors

4R2

and

4R3

providing

the

balance

above

ground.

From

the

secondary

of

trans



former

6T1

the

signal

then

appears

at

the

grid

of

1V1.

Using

the

unbalanced

bridge

arrangement,

transformer

6T1

and

the

first

stage

of

1V1

are

'ERASE

I

ERASE

10JUST

«EAO

1

—

Amplifier

chassis,

rear

view

by-passed,

the

signal

appearing

at

the

grid

of

the

second

stage

through

resistor

4R5

and

across

potentiometer

4R9

with

resistor

4R3

and

4R4

completing

the

circuit

to

ground.

At

the

first

stage,

bias

and

negative

feed



back

is

achieved

by

means

of

unbypassed

resis



tor

1R7.

When

this

first

stage

is

used,

the

am



plified

signal

is

coupled

through

capacitor

1C1

and

potentiometer

4R9

and

resistor

1R8

(in

parallel

)

to

the

grid

of

the

second

stage,

where

further

amplification

takes

place.

Potentiome



ter

4R9

provides

a

means

for

setting

RE



CORD

LEVEL.

Bias

and

negative

feedback

in

the

second

stage

arc

attained

by

unbypassed

resistor

1R11.

Capacitor

1C2A

and

resistor

1R

13

form

a

plate

decoupling

network.

Capa



citors

1C3

and

1C4

and

potentiometer

4R12

(RECORD

CALIBRATE)

provide

record

cali



bration

circuitry.

also

provided

on

the

chassis

back

panel.

When

two

electronic

assemblies

arc

used

for

stereophonic

operation,

the

only

external

differ



ences

are

that

the

slave

amplifier

has

one

fuse

post

instead

of

two

and

the

ac

power

input

receptacle

(J8)

is

not

furnished.

IN

P

-

U

J

TRANSFER

SWITCH

I

-

i

BALANCED

BRIDGE

________

|

UNBALANCED

BRIDGE

___________

6

\

OSC

'ERAS

FROM

2ND

STAGE

OF

T

\>-»T0

JRO

STAGE

I

-------------

I

AOJUS'

REPRODUCE

AMP

LIFIER

REPRODUCE

RECORD

HEAD

^*BiA5

/

ADJUST

BIAS

COUPLING

USED

FOR

TWO

TRACK

STEREOPHONIC

OPERATION

Related product manuals

Preview: Ampex 351 Series

Ampex 351 Series