Table of Contents
Advertisement
INTRODUCTION
The Heathkit model AG- 9 Audio Generator is a simple, yet versatile instrument. While simple
in layout and easy to construct, the carefully assembled instrument provides ease of operation
in a multitude of test setups encountered in audio laboratories.
The wide range of repeatable
frequencies and the metered low distortion output voltages covering nearly all values encoun-
tered in audio work contained in the conveniently small cabinet will entitle this instrument to a
preferred spot in the laboratory.
The excellent performance of which this design is capable will not be realized in the finished in-
strument, UNLESS the assembler uses the best workmanship of which he is capable. Poor sol-
dering technique, corrosive fluxes ( acid core, so-called non- corrosive pastes),
hurried and
careless construction and failure to follow procedures outlined in this manual are the most pre-
valent causes for unsatisfactory operation. Protect your investment in time and money and reap
the reward of personal satisfaction that money cannot buy, by doing a first class job of construct-
ing this kit.
CIRCUIT DESCRIPTION
The circuit of this instrument may be divided into four parts:
the power supply, the oscillator,
the attenuator and the metering circuit.
The power supply uses the conventional power transformer full wave rectifier circuit feeding a
ripple filter consisting of two condensers and a choke.
The oscillator uses a 6AU6 pentode voltage amplifier and a 6CL6 triode- connected cathode fol-
lower. Regenerative feedback from the 6CL6 to the 6AU6 cathode is applied through the tungsten
filament candelabra based lamp.
Degenerative feedback is applied from the 6CL6
through a "notch" network to the grid of the 6AU6.
The resultant oscillation occurs at the "notch"
frequency, where degeneration is minimum and
phase shift is zero.
The "notch" network is a capacitor- shunted
bridged- T type.
The "notch" occurs at a fre-
quency:
F
1
re R
--
F
where C
= A7C
2
The amplitude of oscillation is maintained at a
nearly constant value by the tungsten lamp. The
regenerative feedback is applied through a volt-
age divider consisting of the lamp and the "oscil-
lator" control.
An increase in output signal in-
creases the lamp current, the lamp temperature
and the lamp resistance. This reduces the amount
of feedback applied to the 6AU6 cathode and the
resultant output. A balanced condition is thus obtained. The "oscillator"
control is used to set the nominal output level.
•
VOLTS
o
PHASE
SHIFT
O
The "notch" network consists basically of two resistances and two con-
densers.
From the relationship shown it is evident that a decrease in
capacities by a factor of 10 will increase the frequency by a factor of 10.
As the values of C1 and
C
2
were chosen with a 10:1 ratio, five conden-
sers can do the job of four pair or eight, in achieving four decade ranges.
NEGATIVE
FEEDBACK
POSITIVE
FEEDBACK
FREQUENCY
FREQUENCY
FREQUENCY
OF OSCILLATION
NEC. Fe • POS Fe
PHASE
SHIFT =
TCZ
NOT CH
NETWORK
NETWORK"
Advertisement
Table of Contents
