280B Series

Scully 280B Series User Manual

Scully 280B Series

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Model

285B

Theory

of

Operation

SECTION 4

THEORY OF OPERATION

4.1

GENERAL

4.2

The

285B

theory

of

operation

for

the

tape

transport

is

identical

to

the

280B.

The

electronics

assembly

is

discussed

in

this

section.

4.3

ELECTRONICS

ASSEMBLY

4.4

The

electronics

assembly

consists

of

the

play

head

on

the

tape

deck

and

the

two-channel

audio

amplifier

printed

wiring

assembly.

The

two-channel

audio

amplifier,

Figures

4-1

and

7-1,

contains

two

identical

amplifier

circuits.

The

following

discussion

covers

channell.

4.5

The

audio

signal

from

the

play

head

is

connected

through

Jl14

and

J130,

on

the

play

electronics

assembly,

to

a

preamplifier

circuit

consisting

of

Ql,

Q3

and

associated

components.

High

or

low

speed

equalization

is

selected

by

the

CAPSTAN LOW/HIGH

switch

on

the

trans-

port

control

panel

through

the

transport

logic

PWA

and

applied

to

analog

switch

Ul

and

inverter

Q5.

The

amplifiers

of

Ul

close

the

solid

state

relay

contacts

when

+2.5

to

+5.5

volts

appears

at

their

inputs

and

open

when

0

to

+0.4

volt

appears

at

their

inputs.

Equali-

zation

is

adjusted

by

variable

resistors

R9

(LO)

and

R7

(HI).

The

amplitude

of

the

preamplifier

output

(Q3

collector)

is

adjusted

by

R23

and

applied

to

the

input

of

power

amplifier

U2.

U2

raises

the

level

of

the

equalized

audio

signal

to

provide

the

600-ohm

output

through

the

line

output

audio

transformer

(Tl).

4.6

The

audio

output

of

line

driver

U2

is

also

applied

to

VOLUME

control

RlOl

on

the

transport

control chassis

assembly.

The

wiper

of

the

VOLUME

control

is

connected

by

the

audio

interconnect

harness

4-1

Table of Contents

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Scully 280B Series Specifications

General

Brand	Scully
Model	280B Series
Category	Turntable
Language	English