Heathkit IG 5218 Manual

Page 1

for the

SlNE-SQUARE
AUDIO GENERATOR
Model lG-5218

595-1975-01

'wm,

W V
H mm

1'1
.

HEATH COMPANY - BENTON HARBOR, MICHIGAN

Page 2

INTRODUCTION

The Heathkit Model 10-5218 Sine-Square Audio
Generator has been designed for laboratory use as
well as for service and testing. Sine wave signals are
available between 1 Hz and 100 kHz. Low distortion
(less than .1%) sine wave signals are available be-
tween 1 Hz and 100 kHz. Low distortion [less than
.1%) sine wave signals are available from 10 Hz to 100
kHz. The output is stepped from .003 volt to 10 volts.
These high quality sine wave signals make it ideal for
such applications as testing audio amplifiers for gain
and frequency response, as a signal source for har-
monic distortion measurements, or as an external
modulator for an RF signal generator.

Square wave signals with a rise time of 50
nanoseconds are available from 5 Hz to 100 kHz at
output levels up to 10 volts. These clean square wave
signals can be used for checking frequency response
in audio equipment, or as a trigger for testing digital
instruments.

HEATHKIT®

The sine and square wave frequencies are identical
and the level of each is independently adjustable.
Both signals may be used either simultaneously or
independently.

The sine wave output will operate into high impe-
dance loads (10 kn or higher] in all output ranges, or
it will operate into 600 ohm loads in ranges up to 1
volt. The square wave output is designed to operate
into loads of 2000 ohms or greater.

Other features include: A panel meter for monitoring
the sine wave output; repeatable selection of any fre-
quency; switch-selected 600 ohm internal load; and
all solid-state circuitry for maximum reliability. All of
these features combine to provide you with a ver-
satile, accurate, and attractive signal source. It will be
a valuable and useful addition to your laboratory or
workbench.

Page 4

Page 42

( )Plug the line cord into an .AC outlet.
( ) Turn the POWER switch 0N.

( ) Adjust the FEEDBACK control until the
panel meter reads between 6 and 8 on the
0-10 scale.

( ) Set the external voltmeter to read 10 volts
AC.

( ) Connect the external voltmeter common lead
to the black sine wave output binding post.
Connect the other voltmeter lead to the red
sine wave output binding post.

( ) Rotate the METER CAL control clockwise
until the panel meter reads the same, on
the 0-10 scale, as the voltmeter.

( ) Disconnect the external voltmeter.

NOTE: During the following adjustments the
panel meter pointer may seem to vary errati-
cally. This is normal. If you encounter difficul-
ties, make the control adjustments in small
increments and allow the instrument time to
stabilize after each adjustment.

( ) Turn the SINE WAVE AMPLITUDE control
(fine) to approximately the 3 o'clock posi-
tion.

( ) Adjust the BIAS control until you obtain a
maximum panel meter reading.

( ) Turn the SINE WAVE AMPLITUDE (fine)
control fully clockwise.

( ) Adjust the FEEDBACK control until the
panel meter reads 10 volts.

NOTE: In the following two steps, if no change
can be detected in the panel meter reading, it
will not be necessary to readjust the feedback
control.

( ) Turn the TENS FREQUENCY switch to each
position, 10 through 100. Leave the switch
in the position where the panel meter indi-
cates the lowest voltage.

( ) Turn the MULTIPLIER switch to eachposi-
tion, X1 through X1000. Leave the switch
in the position where the panel meter indi-
cates the lowest voltage.

HEATHKIT

( ) Readjust the FEEDBACK control until the
panel meter indicates 10 volts.

This completes the adjustments of the Audio
Generator. Turn off the power and remove the
AC plug from the socket. Proceed withthe Final
Assembly on Page 45.

ADJUSTMENTS WITH AC VOLTMETER AND
OSCILLOSCOPE

Set the controls and switches as follows:

( ) POWER SWITCH: OFF.

(WMULTIPLIER: X100.

(TENS FREQUENCY: 10.

( ) UNITS FREQUENCY: 0.

( ) FREQUENCY control: 0.

NOTE: The word FINE on the front panel refers
to the small knob on each of the AMPLITUDE

controls, COARSE refers to the large knob on
each of the AMPLITUDE switches.

(J) SINE WAVE AMPLITUDE switch (coarse):
10 volts.

(J) SINE WAVE AMPLITUDE control (fine):
Fully clockwise.

( )SQUARE WAVE AMPLITUDE
(coarse): 10 volts.

switch

) SQUARE WAVE AMPLITUDE control (fine):
Fully clockwise.

(
() 600 n LOAD: EXT.

NOTE: The following controls are located on
the wave generator circuit board. Refer to
Figure 1 (fold-out from Page 36) for their loca-
tion. Position each control at its center of ro-
tation.

(1) BIAS.

or") FEEDBACK.
(4 ) SYMMETRY.

(U) METER CAL.

Page 14

CIRCUIT DESCRIPTION

Refer to the Block Diagram on Page 65 and to the
Schematic Diagram (fold- out from Page 75) while
reading this Circuit Description.

The circuit of the Sine-Square Audio Generator

includes three principal sections: The Sine Wave
Generator (including the meter and output attenu-
ator circuits), the Square Wave Generator and
the Power Supply. Each of these Sections will be
described separately.

SINE WAVE GENERATOR

The sine wave oscillator circuits consists of
differential amplifier transistors Q1 and Q2;
voltage amplifier transistor Q3 ; power amplifier
transistors Q4 and Q5; and the positive and
negative feedback loops. Positive (regenerative)
feedback comes from the common emitter output
of transistors Q4 and Q5, and is coupled to the
base of transistor Q2 through the lamp L1, the
arm of feedback control R7, and resistor R6.
Negative (degenerative) feedback comes through
the notch filter and is directly coupled to the
base of transistor Q1.

Oscillation occurs due to the positive feedback.
Without negative feedback, the circuit would
oscillate at some indeterminate frequency; how-
ever, the notch filter, which passes all fre-
quencies except the one to which it is tuned,
provides the negative feedback to the base of
transistor Q1. This negative feedback prevents
oscillation at all frequencies except the one that
is not passed, permitting the system to oscil-
late at only the selected frequency,

HEATHKIT®

The tuned frequency of the RC notch filter
circuit may be calculated by the general formula:

where F is frequency in hertz, R is resistance
in ohms, and C is capacitance in farads. How-
ever, since this notch filter is a specialized RC
network in which there are two resistances and
two capacitances, the formula for this network
then becomes:

1

m Rlechlc .

Since R1 and R2 will always be equal, the for-
mula simplifies to:

F:

1
27TRJC1CZ .

F:

63