Bauer 707 User manual

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ELECTRONICS
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098-1165-01
------------
•
AM
BROADCAST TRANSMITTER
MODEL 707
INSTRUCTION
BOOK
Electronic
Corporation
5851
Florin-Perkins
Road
(916
-
383-5353)
Sacramento,
California
95828
A
DIVISION
OF
COMPUTE!'
~auiPMENT
CORPORATION
•
I
July
1970

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,·
·
TABLE
OF
CONTENTS
DESCRIPTION
OF
CIRCUIT FUNCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . • . . 3
Radio
-
Frequency
Section
. . . . . . . . . . . . . . . . . . . . . . . . . . .·. . . . . . . . . 3
Audio
Section
. . . . . . . . . . . . . . . . . . . . . . • . . • . . . . . . . . . . . . . . . . . . 4
Power
Suppl3/
Systems
. . . . • . . • . . . . . . . . . . . . . . . . . . . . . . • . . • . . • . 4
Power
Control
Circuits
. . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . 4
Metering
Circuits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . 6
INSTALLATION INSTRUCTIONS . . . . . • . . . • . • • . . • . . . . . . ... . . . . . . . • . 6
Environment
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . • . . . 6
External
Connections
. . . . . ... . . . . . • . . . • . . . . . . . . . . . . . . . . . . . . . . 6
Internal
Connections
·. . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . • . . . . 7
INITIAL ADJUS1MENTS
AND
TUNING . . . . . . . . . . . •. • . . . . . . . . . . . . . . . .
8
MAINTENAi~CE AND TROUBLESHOOTING . . . . . . . . . . • . . . . . . . . . . . . . . . 11
REMOTE CONTROL
...
.
............
.
...
,
•.•.....
, . . . . . . . . . . . 11
GENERAL SERVICE INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Safety
Notice
. . . . . . . . . . . . • . . . . . . . . . • . . . • . . . . . . . . . . . . . . . . . 13
Production
Changes
..
.
....
.....
.
.....•.
'.
• . . . • • . . . . . . . . . . . . • 13
Replacement
Parts
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . 13
Warranty . . .
....
~-. . . . . . . . . . . . . . . . . . . . . . .
..
.. ·. . . . . . . . . . . . .
14
LIST
OF
TABLES
Number
Page
1
Summary
of
Mechanical
and
Electrical
Specifications
. . . • . . . . . . . . 1
2 ·
Typical
Transmitter
Performance
Data,
Bauer
Model
707.
. . . . . . . . .
15
3
Parts
List
. . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . .
16
4·
Tuning
Chart,
Model
707 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
5
Power
Determining
Parts-
-
1000/250
Watts;
1000/500
Watts
.....
.
..
27
6
Cable
Table,
Low
Voltage
Harness
. . . . . . . . . . . . . . • . . • . • • . • . 28
680215.2
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Number
1
2
.3
4
5
6
7
6$0215.2
LIST OF ILLUSTRATIONS
Model 707 AM Transmitter ...... .
Pao-e
::..::£.::_
iv
Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Latching Relay Unit - Rust Model 108-4A . . . . . . • . . . • . . . . • . . • . 12
Front View of Bauer Model 707 Broadcast Transmitter. . . . . . . . . . . . 36
Rear View of Bauer Model 707 Broadcast Transmitter . . . . . . . . . . . . 37
Outline Drawing .................. · ............ ~ . . . . . . 38
Schematic Diagram
. . . . . . . 39
' .
Page iii

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Figure 1. Model 707 AM Transmitter.
68021 5.2
Page iv

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Table
1.
Summary
of
Mechanical
and
Electrical
Specific
'
Type
of
Emission:
Rated
Power
Output:
Power
Output
Capability:
RF
Output
Impedance:
Frequency
Range:
Frequency
Stability:
Audio
Input
Level
(100%
mod):
Audio
Input
Impedance:
Frequency
Response
(0-95%
mod):
1000/500/250
watts
50-10,
000
cps
30-12,
000
cps
Distortion
(0-95%
mod):
1000/500/250
watts
50-10,
000
cps
Carrier
Shift
1000/500/250
watts:
_
Noise
Level
(below
100%
mod):
FCC
Efficiency
Factor
(F):
Power
Consumption:
(for
one
kilowatt
carrier
power)
Average
modulation
100%
modulation
Power
Requirements:
680215.2
.
.
.. '
A3
1000/500/250
watts
llOO
watts
50
ohms,
unbalanced
540-1600
kHz
.
± 5
cps
+
10
dbm
600
ohms
±
0.
5
db
±
1.5
db
2.
0%
max
less
than
3%
-55
db
0.70
3300
watts
3950
watts
208-230
volts,
60
cycles,
single
phase,
90%
power
factor
Page
1 .

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L.
Table
1.
Summary
of
Mechanical
and
Electrical
Specifications
inued).
Dimensions
:
Net
Weight
;
Heigh
t 75
inches
, Width 34
inche
s,
Depth
25
inches
800
poW1ds
Ambient
Temperature
Range: -
20°
to
+110°F
Altitude Range:
0-8000
feet
RF
OUTPUT
)
CRYSTAL BUFFER
DRIVER
P
OWER
AMPLIFIER
OSCILLATOR AMPLIFIER AM?LIFIER
(2)
4-400A
6AG
7
6AG7
6CA7
1·
-
-;
-,.-
<;>
AUDIO
I
AUDIO
MODULATOR BUILT-IN
NPUT
~
AMPLIFIER
(2)4
-
400A
DUMMY
(2 )
6SJ7
ANTENN
A
LOW-VOLTAGE BIAS
HIGH-VOLTAGE
RECTIFIER RECTIFIER
REC
TIFIER
SO
L.
ID
STATE
S
OLID
ST
AT
E SOL
ID
STATE
Figure
2.
Functional
Block
Diagram.
680215. 2
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DESCRIPTION
OF
CIRCUIT FUNCTIONS
The
Bauer
Model
707
AM:
Broadcast
Transmitter
employs
high
-
level
modulation
and
can
operate
on
any
carrier
frequency
in
the
range
from
540 kHz
to
1600
kHz.
With
modi
-
fications
,
operation
can
be
extended
to 30 MHz.
The
transmitter
is
normally
supplied
pre-tuned
to
th~
desired
channel
.
The
frequency-deter~1ining
components
for
the
trans
-
mitter
are
listed
in
table
4.
Bi-level
power
operation
is
standard
with
this
transmitter
which
can
be
switched
instantly
between
any
tv-10
of
the
following
three
power
levels
:
250
watts,
500
watts,
1000
watts.
Component
values
that
establish
the
two
operating
power
levels
are
given
in
table
5.
A
functional
block
diagram
is
given
in
figure
2;
the
schemat
ic
is
shown
in
figure
7.
Radio
-
Frequency
Section
The
radi
o-
frequency
portion
of
this
transmitter
begins
with
Type
6AG7
crystal
oscillator
Vl.
For
emergency
operation,
a
second
crystal
may
be
switched
into
the
oscillator
circuit
by
means
of
relay
K6.
The
oscillator
drives
Type
6AG7
buffer
amplifier
V2.
The
cathode
circuit
of
V2
supplies
unmodulated
RF
at
jack
Jl
to
operate
any
standard
frequency
monitor
·.
The
entire
oscillator/buffer
asse
'
mbly
is
constructed
in
a
removable
shielded
chassis
.
The
buffer
output
excites
Type
6CA7
RF
driver
tube
V3.
·
Resistor
Rl2
in
the
cathode
circuit
of
V3
controls
the
gain
of
the
driver
stage
and
determines
the
amount
of
RF
drive
available
at
the
grid
of
final
power
amplifiers
V8
and
V9.
Plate
and
screen
voltage
on
the
final
power
amplifiers
is
varied
by
the
modulator
to
produce
amplitude
modulated
radio
-
frequency
output.
Plate
choke
L6
and
capacitor
C22
prevent
RF
power
from
feeding
back
into
the
modulator
and
power
supply
portions
of
the
transmitter
.
The
RF
signal
appearing
across
capacitor
C25
and
a
small
portion
of
tank
L7
is
coupled
into
a
Tee
matching
network
consisting
of
LS,
C26,
and
L9
.
The
location
of
the
output
tap
on
L7
is
selected
so
that
the
combination
of
C25
and
the
lower
portion
of
L7
form
a
low
impedance
circuit
at
the
second
harmonic
of
the
carrier
where
necessary
to
provide
optimum
suppression
of
second
-
harmonic
radiation
.
The
radio
-
frequency
output
fr
om
the
Tee
matching
network
can
be
switched
to
a
built-in
dummy
load
by
means
of
switch
S8
.
The
load
tap
on
coil
L9
is
automatically
shifted
slightly
when
the
output
is
switched
to
the
dummy
to
compensate
for
the
small
amount
of
residual
inductance
inherent
in
the
dummy
load.
S8
is
constructed
to
allow
the
insertion
of
an
RF
ammeter
for
use
during
the
initial
tune
-
up.
M4
is
an
0-1
ma
DC
meter
~ith
a
0-6
RF
ampere
scale
intended
to
be
used
with
a r e
mote
diode
for
metering
antenna
cur
r
ent.
The
transmitter
is
designed
to
feed
a non-
reactive
50
ohm
unbalanced
load
. Non
-standard
load
impedances
can
be
accommoda.ted
with
a
matching
network
external
to
the
pressurized
transmitter
cabinet
.
680215.2
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....__,.____,,
Audio Section
The audio portion of the Model 707 Transmitter consists of push -pull Type 6SJ7
amplifier tubes V4 and VS, which drive push -pull Type 4 -4 00A modulator tubes V6 and
V7 operating class AB-1. The audio level supplied to input transformer T6 is controlled
by the operation of relay KS so that the degree of modulation remains unchanged when
switching between the t\vo power levels . Balance control R46 serves to balance the
audio levels fed to the grids of V6 and V7 for minimum distortion . Bias control R27
establishes the modulator plate current under conditions of no modulation. Inverse
feedback around the two audio stages is provided by two voltage dividers . The combination
of R55 and R43 returns a portion of the output voltage of V6 to the grid circuit of VS.
Similarly, R58 and R44 return a portion of the output of V7 to the grid of V 4. The resistanc e
values establish the amount of audio feedback at 8 db. The audio 9utput voltage appearing
across ~e secondary of modulation transformer T7 produces amplitude modulation by
alternately adding to and subtracting from the DC voltage applied to the final RF power
a~plifier .
Power Supply Systems
Three separate power supply systems provide the DC voltages necessary for operation
of the transmitter. High-voltage plate transformer Tl drives a bridge rectifier consisting
of two plug-in rectifier assemblies . The rectified high-voltage output is filtered and used
to supply plate voltage to the . four 4 -400A tubes and screen voltage to the final RF stage.
For 500 watt operation, series resistors are added to reduce the final plate and screen
voltages. For 250 watt operation, increased efficiency is obtained by operating half of
·- • the high-voltage rectifier independently of the normal bridge circuit to produce half-
voltage output for the final amplifier. A second section of filter (LlO, C46) is added
during 250 watt operation to maintain low hum level at the lower power. A plug-in bias
rectifier consisting of a single silicon diode package Dl supplies negative bias voltage
to the grids of modulator tubes V6 and V7. Another bridge rectifier consisting of silicon
diodes D2 through Dl7 provides DC for audio amplifiers V4 and VS, RF driver V3, and
the screens of modulators V6 and V7. Diodes D2 through DS and Dl~ through Dl 7 also
function as a conventional full - wave rectifier to deliver a l ower value of DC voltage at
terminal 5 of transformer TS which is filtered through Ll8 and C27 to provide power for
Vl, V2, and the screen of V3.
Power Control €ircuits
Unlike tube -type rectifying systems, no time delay relays are required to prevent the
premature application of high voltage to the rectifiers. This considerably simplifies
the control and relay circuits. Power at 230 volts, single - phase, is supplied to the
transmitter through main line fuses F6 and F7. Actuation of master-start switch Sl
picks up relay Kl which in turn applies power to the primary of voltage regulating trans -
former-T2 and to the blower. When door interlock Sll is closed, the operation of switch
S2 applies power to the primary of low - voltage and bias rectifier transformer TS. With
680215.2
Page 4

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power
supplied
to
TS,
all
of
t:1-i"e
iow-level
stages
Vl
through
VS
will
f on
and
the
RF
drive
supplied
by
V3
will
produce
sufficient
grid
cu
rrent
in
the
final
am
pli
fier
to
operate
grid
under-drive
relay
K2. When
sufficient
RF
drive
is
present
to
operate
rel
ay
K2
it
is
then
possible
to
operate
high
-
voltage
supply
contactor
K7
(if
high-voltage
door
interlocks
S9
and
S10
are
closed)
when
the
high-voltage
switch
S4
is
clo
sed
.
This
also
requires
that
the
overload
relay
be
in
reset
position
.
In
normal
operation,
both
the
low
and
hi
gh
voltage
switches,
S2
and
S4,
are
left
turned
on
and
the
entire
transmitter
is
co
ntrolled
by
master-start
switch
Sl.
Auxiliary
contacts
on
relay
K7
prevent
the
application
of
full
screen
voltage
to
the
modu
-
lator
tubes
before
the
plate
voltage
has
been
applied
.
Overload
relays
K8,
K9,
and
KIO
,
will
de-energize
relay
K7
and
remove
high
voltage
plate
power
in
the
event
that
there
is
excessive
current
in
the
cathode
circuit
of
the
final
amplifier,
in
.
the
cathode
circuit
of
the
modulators,
or
in
the
primary
of
plate
transformer
Tl.
Adjustable
shunting
resistors
Rl6
and
R59
control
the
sensitivity
of
overload
relays
K8
and
K9.
The
improved
"Silconetic"
overload
relays
utilize
a
special
silicone
damping
fluid.
They
provide
instantaneous
opera-
tion
on
large
over
_
loads
and
delayed
operation
on
small
but
sustained
overloads.
As
a
result,
superior
overload
protection
is
achieved
while
avoiding
nuisance
outages
caused
by
short-term
transients
such
as
power
line
surges
or
isolated
peaks
of
overmodulation
which
would
not
damage
the
transmitter.
In
case
of
an
overload,
flags
are
extended
by
the
overload
relays
to
indicate
which
circuit
is
involved
.
The
operation
of
any
one
of
the
three
overload
relays
removes
primary
power
which,
in
turn,
eliminates
the
overload
current
and
restores
the
overload
relay
to
the
normally
-c
losed
position
.
Repetitive
re
-
cycling
of
the
overload
relays
and
of
contactor
K7
.
is
prevented
(in
the
event
of
a
sustained
overload)
by
an
"
overload-lockout"
circuit
consisting
of
latching
relay
K3
and
associated
components
. When
any
of
the
overload
relays
operate
,
the
voltage
across
its
normally-
closed
contacts
is
applied
to
diode
rectifier
D77
to
change
c
apacitor
C43.
When
sufficient
voltage
appears
across
C43,
relay
K3
will
latch
open
its
normally-closed
c
ontacts
to
prevent
prolonged
repetition
of
re-cycling.
The
time
required
to
build
a
sufficient
charge
on
C43
to
actuate
K3
is
adjusted
by
rheostat
R61.
This
is
normally
set
so
that
the
over
-
load
relays
will
re-cycle
three
times
before
K3
operates.
When
the
cause
of
the
overload
has
been
cleared;
momentary
manual
operation
of
overload
r
eset
switch
S3
serves
to
energize
the
reset
coil
on
K3
and
restore
it
to
the
normally
-cl
osed
condition.
The
air
flow
switch
S12,
located
in
the
tube
compartment,
is
connected
to
remov
e
filament
and
low
voltage
power
should
air
loss
be
experienced.
Small
adjustments
in
operating
power
are
made
with
motor
-driv
en
rh
eostat
Rl
9
in
the
cathode
circuit
of
the
final
amplifier.
Power
is
raised
or
lowered
through
the
momentary
operation
of
switch
SS
which
determines
the
direction
of
rotation
of
the
power
control
moto
r.
The
large
change
in
power
necessary
when
switching
to
the
lower
of
the
two
power
levels
provided
by
the
transmitter
is
accomplished
through
the
operation
of
switch
S6
which
actuates
power
c
hange
relays
K4
and
KS. Ooe
set
of
contacts
on
relay
KS
is
used
to
reduce
the
audio
input
to
the
transmitter
so
that
the
same
degree
of
modulation
is
maintained
. I . •
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680215.2
Page
5