Heathkit IG-18 User Manual

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Page

64

In

the

notch

filter

in

the Audio

Generator

R

may

consist

of one

or

several

resistors

in

parallel;

or

R=

;::

C

y

•

re'pr1eSI:mt:s

the

resistance

value

selected

the

Tens

Frequency

switch

for

a

fre-

quency.

This

resistance

may

consist

of one

re-

sistor,

or

a combination of

several

resistors.

For

for

20

Hz

the

two 5000 n

resistors

are

selected

and

Rx

;::

5000

for

40

Hz the two 2500 n

resistors

are

and

;::

2500

n,

for

60

Hz both the 5000 n the

2500

n

resistors

are

selected

in

<laJl

dLJ.ea

;::

1670

n.

Ry

represents

the

resistance

value

selected

th~

Units

Frequency

switch

for

aparticularfre-

quency.

The

operation

of.

this

switch

is

identical

to

that

of

the Tens

Frequency

switch,

that

the

resistance

values

are

ten

times

those

of

the

Tens

Frequency

switch.

R

z

represents

the

resistance

value of the

Frequency

when

adjusted

for

frequency.

and

represent

the

CalJa(~lt()rs

tiplier

switch. The

value

of C

10

times

larger

than

the

value

positions

of the

Multiplier

::;WllL:;'l.

As shown in the

general

formula

F

tuned

frequency

of a notch

filter

is

;n,,,,::,,,,,,,::,l,,

proportional

to

the value of

its

resistances

and

capacitances.

Therefore,

to

achieve

an

increase

in

frequency

the

resistance

decrease.

for

a tenfold

increase

using

Multiplier

switch,

must

decrease

tenfold.

Any tendency of

the

oscillator

i'/,\,nvo."\rh",,,

"''''IS,''''''''''

of

increaSing

is

controlled

by

If

the

output

increases,

more

cur-

rent

is

fed

the

feedback

circuit

and

through

increased

current

causes

the

filament

of the

lamp

to

heat

slightly, which

causes

its

resistance

to

This

increase

in

resistance

attenuates

the

feedback to

the

base

of

transistor

The

result

is

a

regu-

lated

from

transistor

DC

base

bias

is

provided

to

Ql

and

voJXa~re

divider

that

consists

of

resistors

and

control

R7. (ReSistor R3

decreases

gain

of the

differential

amplifier

to

make

"'LGU/Le.,

The voltage

at

the

lower

end of

this

and

therefore

at

the

bases

of

Q1

and

adjustable

by being

connected

to

the

arm

Bias

control

R9, which

is

connected

in a

DC

volt.

age

divider

with

R8

and RIO.

The Signal

from

the

differential

amplifier

is

di·

rect

coupled

from

the

collector

of

Q2

to

the baSI

of voltage

amplifier

transistor

Q3.

From

the col·

lector

of Q3,

the

signal

is

direct

coupled

to

thi

base

of and

through

diodes

Dl

and

D2

to

thl

base

of

These

diodes

maintain

a 1.2 vol

difference

between

the

bases

of

transistors

Q'

and

form

an

emitter

follower

ml;:nt:ary-pair

amplifier

with no voltage

Impeliarlce output. The output Signal

fron

coupled

to

the

square

wave

circuit.

t1"i('n:,.~,l"

and to

the

sine

wave,

OUTPUT ATTENU,ATOR

sine

wave Signal

from

is

cmrpliel

tn,,,,,,

••

,.,.n

capacitor

C6

to

Sine Wave

Arnp:Utllldl

control

RI06.

From

RI06,

the

through

isolating

resistor

circuit

and

to

the

Sine Wave Anopllittlde

swncn

The

resistor

network

sections

of thi,

switch

comprise

an

voltage divide:

(RI09

to

which

proportionately

divide:

the of 10 dB each.

The

selectel

volta.lre

level

is

to the

sine

wave outpu

The

rem

aining

section

of the switcl

internal

load

resistor

R122

to

be con,

neeted

across

the

output

terminals

in the

st

lowest

output

ranges.

CIRCUIT

Resistor

RIOa and

meter

calibration

control

R2]

a voltage

divider

through

which

somE

of

the

signal

from

resistor

RI07

is

bypassedfm

monitoring

by

the

panel

meter.

Diodes

D3

and

D4.

and

load

resistors

R24 and R25

form

a half-wavE

bridge

rectifier

circuit

for

the

output

meter,

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Heathkit IG-18 Specifications

General

Brand	Heathkit
Model	IG-18
Category	Test Equipment
Language	English

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