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
' .
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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
Page
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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

www.SteamPoweredRadio.Com
when
going
to
lower
power.
A
second
set
of
contacts
on
relay
in
serts
an
add
itiona
l
resistance
Rl3
in
the
cathode
circuit
of
RF
driver
V3 to
reduce
the
RF
drive
to
the
final
power
am
plifier
stage.
The
operation
of
relay
K4
serves
to
reduce
the
pl
ate
and
screen
voltage
applied
to
the
final
power
amplifier
for
lower
power.
Corr
ection
of
·
modulation
monitor
feed
when
changing
power
is
a
ccomplished
by
relay
K-11
and
adjust-
able
resistor
R-75.
Terminals
are
provided
to
fa
cilitate
the
connection
of
remote
controls
on
all
necessary
operating
switches.
Meteri
ng
Circuits
Voltage
or
curr
en
t
meters
are
provided
for
all
important
circuits
and
remote
metering
facilities
are
built
into
the
transmitter
so
that
plate
volt
age
and
plate
current
for
the
final
power
amplifier
c
an
be
metered
by
any
conv
en
tional
remote
co
nt
rol
system
without
adding
accessory
metering
units
within
the
transmitter
.
For
added
safety
and
to
pr
event
the
accumulation
.
of
dust,
the
final
plat
e
curre
nt
meter
M3
,
is
kept
at
a
low
potential.
Thi
meter
in
the
cathode
circuit
of
the
final
amplifier
rea
ds
combined
pl
at
e
an
d
screen
curren
t
The
value
of
net
plate
current
can
be
obtained
by
subtracting
the
screen
current
indicated
by
meter
M6.
The
references
in
the
Federal
Communications
Commission
Rules
to
final
efficiency
do
not
consider
the
screen
power
supplied
to
the
final
amplifier.
The
net
pl
a
te
current
sh
ould
accordingly
be
used
in
an
y
calculations
of
efficiency
in
comparison
to
the
FCC
efficiency
factor
(F).
INSTALLATION INSTRUCTIONS
Environment
Install
the
tr
ansmitter
in
a
well-ventil
at
ed
room
which
is
reasonably
free
from
moisture
and
dust.
Particular
care
should
be
given
in
remote
control
installations
to
obtain
adequat
room
ventilation
and
to
prevent
the
ambient
temperature
from
rising
to
dangerously
high
levels.
'
l.
External
Connection
s
Conn
ect
a
low
-
resistance
ground
to
the
transmitter
frame
using
any
of
the
base
assembly
bolts.
Remove
paint
at
all
points
of
contact
to
obtain
a
good
connection.
On
smooth
wooden
floors,
an
alter
na
tive
method
is
to
remove
paint
from
the
bottom
of
the
base,
set
the
front
edge
of
the
transmitter
base
on a
length
of
copper
strap,
and
anchor
the
transmitter
with
lag
screws
extending
through
the
base
and
the
copper
strap
.
2.
Connect
a 230
volt,
60
cycle,
single-phase
supply
to
the
transmitter
fuse
block
using
number
10
wire
.
The
safety
disconnect
S\Vitch
or
circuit-bre
ak
er
supplying
the
transmitter
sho1:Jld
be
rated
at
30
amperes.
The
utility
transformer
feeding
the
transmitter
should
have
a
capacity
of
5
kva
or
more
to
provide
adequate
regulation
for
minimum
carrier
shift.
680215.2
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3.
A hole has b~e~ provided · in the b. ottom ·of the cabinet near T-7 l ccomm~d ate
an RF output transmission line . such as RG-8/U or 1/2" Foamflex. The line
can enter the trans .mit ter cabinet at the top if desired. Any hole drilled to
accommodate the transmission line should be no larger than necessary so as
to maintain air pressure. It is important that the outer conductor be securely
grounded at a point near the termination of the inner conductor.
4 •. Connect the frequency monitor to frequency monitor output jack Jl. If unused,
jack Jl should be shorted to prevent spurious oscillations.
5. Connect the modulation monitor to modulation monitor output jack J2.
6. Connect 600 ohm audio output to terminals l and 2 of TBl. _
Internal Connections
To minimize transportation damage, the heavier components are normally re~oved from
the transmitter prior to shipment. Reinstall these as follows:
1. Install modulation transformer T7 in the rear corner of the cabinet below C-32.
Terminals l, 2, and 3 should be toward the rear of the cabinet.
a.
Connect wire N_ o. 164 to terminal No. 1.
b.
Connect wire No.
155 to terminal No. 2.
c.
Connect wire No. 165 to terminal No.
3.
d. Connect wire No.
154 to terminal No. 4.
e.
Connect wire No.
156 to terminal No. 5.
2. · Install high-voltage transformer Tl in the rear corner underneath the door inter -
lock switches with the primary terminals toward the rear of the cabinet.
a. Connect wire No. 162 to high-voltage center tap · (terminal 7).
b. Connect wire No. 158 to one side of high-voltage (terminal 6)•
.
c. · Connect wire No. 159 to other side of high-voltage (terminal 8).
d. Connect wire No. 129 to primary± tap (terminal 1).
e. Connect wire No. 130 to primary 230 volt tap (terminal 5).
680215.2
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,,,..--..,__
· 3. Install modulation choke Ll2 in the remaining space on the transmitter floor
with the terminals toward the front of the cabinet.
a. Connect wire No. 153 and No. 156 to left-hand terminal (as viewed from
the rear of the transmitter).
b. Connect wire No. 163 to right-hand terminal.
4. Install Sola voltage regulating transformer T2 on the four shock mounts attached
to the side of the cabinet adjacent to the door- interlock switches . Add grommet
to top knockout hole nearest the front panel if not already installed -.
a. Connect wire No. 14 to terminal Hl.
b. · Connect jumper between terminals H2 and H3.
c. Connect wire No. 15 to terminal H4.
d. Connect wire No. 20 to terminal Xl.
e. Connect wire No. 21 to terminal X2.
5. Install all tubes, making sure that the skirts of the 4-400A tubes clear the chassis
holes and seat firmly on the ceramic sockets. Connect 4-400A plate caps.
6. Install main crystal in the right-hand socket (as is viewed from the rear) on the
oscillator/buffer chassis.
7. Install auxiliary crystal used.
INITIAL ADJUSTMENTS A.1'\JD TUNING
Remove high-voltage rectifiers, CB12 and CB13. Set front panel switches as follows:
Low voltage - OFF; high voltage - OFF; high - low power control -LOW; crystal switch -
No. l.
With 230 volts supplied to the transmitter, oper~te the master - start switch Sl. This
should close relay K 1, start the blower and light the 4-400A filaments. Close all doors
to actuate the interlocks. Turn on low voltage switch S2 activating the low voltage
supplies including filament power for all small tu.bes. When the tu.bes have heated, there
should be normal current indications on the four lower front panel meters. Compare
I
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680215 .2
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these meter readings at both i'ow and high power with those tabulated in tab 1e 2 and,
if nec;essary, adjust the final grid current to the indicated value through adjustment of
final drive control Rl2, The final grid tuning coil LS (located in the tube compartment
to the right of V9) does not normally require adjustment but should be checked if the
correct value of grid drive and driver plate current cannot be obtained within the range
of control Rl2. The optimum adjustment of LS will result in maximum final grid current
with minimum driver plate current.
To prepare for the next step, operate power control switch S5 to place the arm of power
control rheostat Rl 9 in the center of its range.
With the transmitter master-start switch turned off, place the antenna/dummy switch
S8 in the DUMMY position. Set R61 on CB4 fully counterclockwis.e. Install high -voltage
diode rectifier boards CB12 and CB13. Adjust bias control R27 for maximum modulator
bias by rotating fully counterclockwise. With the high -voltage switch remaining off and
the high/low power control switch in the low position, energize the master-start switch.
When normal final grid current is obtained, turn on the high - voltage switch. The final
plate voltage meter should now indicate approximately 1500 volts . Adjust the final plate
tune control for minimum plate current and tune through both sides of the "dip" to make
certain that the variable capacitor has not reached the limit of its range . If an RF out-
put meter is used, it should now indicate. With no audio yet applied to the transmitter,
adjust bias control R27 to set the modulator plate current at the value indicated for low-
power qperation in tab 1e 2. If all meter readings are now in substantial agreement
with the typical value
9,
the high/low switch can be changed to high and all meter readings
compared with those tabulated in table 2 for high-power operation.
If the final plate voltage differs by more than 100 volts from the typical value, correct
by means of the primary taps on high-voltage plate transformer Tl. If the final plate
current differs materially from the typical value, it may be necessary to change the final
loading slightly to obtain maximum efficiency. Changes in loading are accomplished by
moving the C23 and C24 taps on the final tank coil L 7. The output tap on L7 should not be
changed because this adjustment must remain fixed for maximum second-harmonic
attenuation. Increasing the tank inductance results in lower tank current and looser
coupling. Any change in tank inductance will require retuning the tank capacitor for
minimum plate current. All loading and tuning changes should . be made in small increments
and at low power because larger departures from plate tanlcre . sonance will produce excessive
final plate current and operate the overload relays . Care should be taken not to place a
strain on the vacuum variable capacitor by turning the drive mechanism beyond minimum
capacity (clockwise). ·. Care should also be taken not to unscrew the drive mechanism past
the point of maximum capacity (counterclockwise). This condition is indicated by a slight
reduction in torque and a sudden loosening of the dust cap inside the tube compartment.
Normally the C23 an4 C24 taps connect to the same turn on the tank coil but finer loading
adjustments may finally be made by moving them independently through a separation not
\.
680215.2 Page 9

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ol
,.
..
exceeding
two
or
three
turns.
Optimum
loading
exists
when
the
rated
RF
output
current
can
be
obtained
with
the
least
plate
current.
To
obtain
best
efficiency,
the
final
tuning
capacit,or
should
then
be
tuned
slightly
clockwise
from
the
minimum
plate
current
position
~o
increase
plate
curre
nt
by
20
ma.
Refer
to
tab
1
e
4
for
normal
tuning
adjustments
.
After
optimum
loading
has
been
established
and
all
meter
indications
are
in
substantial
~greement
with
tab
1
e
2,
the
transmitter
audio
performance
should
be
checked
by
means
of
a
modulation
monitor
and
distortion
meter.
It
is
recommended
that
these
measurements
be
made
by
using
a
suitable
audio
oscillator
having
negligible
distortion
fed
dir
ectly
into
the
transmitter
in
put
terminals
without
benefit
of
any
other
amplifying
equipment
. Any
discrepancies
in
subsequent
overall
system
measurements
are
then
logically
attributable
to
the
equipment
external
to
the
transmitter
or
to
the
manner
in
which
the
external
equipment
is
used.
Although
any
good
4-400A
tube
will
operate
satisfactorily
in
any
of
the
four
tube
positions
,
the
lowest
carrier
noise
will
be
obtained
by
selecting
the
tubes
for
the
final
RF
stage
while
making
noise
measurements
.
Adjust
balance
control
R46
for
minimum
distortion
at
85%
modulation
with
3000
cycles
.
If
m
ini
mum
distortion
occurs
at
the
end
of
R46
rotation,
select
a
different
pairing
of
6SJ7
audio
amplifier
tubes.
If
no
distortion
meter
is
available,
set
R46
at
mid-range.
The
overload
circuits
should
now
be
checked.
With
the
transmitter
operating
on
high
power,
detune
the
final
until
the
final
plate
and
screen
current
is
600
ma.
The
plate
overload
should
operate
within
one
to
two
seconds
.
If
necessary,
readjust
relay
shunt
Rl6
to
get
this
condition.
Res
tor~
tuning
to
normal.
Increase
7500
cycle
audio
input
to
obtain
500
ma
of
modulator
plate
current
.
The
modu"
lator
overload
relay
should
operate
within
one
to
two
seconds
.
If
necessary,
readjust
elay
shunt
R59
to
get
this
condition.
The
"overload
lockout"
circuit
should
now
be
adjusted.
Set
R61
on
CB4
to
mid-range
and
produce
a
large
plate
current
overload
by
detuning
the
final
amplifier
.
The
over
-
load
relays
should
recycle
several
times
before
K3
latches
open.
Proceed
to
adjust
R61
in
small
increments
until
overload
relays
recycle
not
more
than
three
ti
mes
before
K3
latch
es
open,
remembering
that
CW
rotation
of
R61
increases
the
number
of
recycles.
mot)
f With
transmitter
on
low
power,
set
modulation
monitor
carrier
level
to
100.
Then,
fr!D.1;' -
~witching
to
high
power,
adjust
R-75
so
that
carrier
level
again
reads
100.
'
.----...,
The
transmitter
is
now
ready
to
be
switched
to a
properly
adjusted,
non-reactive,
50-
ohm
load.
Change
the
dummy/antenna
switch
S8
to
the
ANTENNA
position
.
If
the
antenna
load
is
near
50
ohms
and
is
non-reactive,
the
loading
and
.
the
point
of
C24
resonance
will
remain
unchanged.
The
transmitter
is
now
ready
for
routine
operation
.
680215.2
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MAINTENANCE AND TROUBLESHOOTING
Periodic inspection will often reveal a condition that may lead to an eventual component
failure. After shutdown of the equipment check the operating temperatures of all of the
major components . It~ms such as the constant voltage transformer and high wattage
resistors are expected to run warm. Most other components do not and you should
attempt to develop a feel for their normal operat i ng condition. Dirt is the major enemy
of all electronic equipment. A routine cleaning of the air filter is a necessity . A soft
dust brush augmented with a vacuum cleaner should be used as often as nec essary to
prevent any accumulation of dust within the cabinet. Wipe up any silicone fluid that may
leak out of the mod u lation transformer . Slight seepage is not harmful .
A routine check of all meter readings is most helpful. Use thein as a guide to tube re-
placement which is the major component problem in any radio transmitter. Develop a
tube log and keep track of the hours a tube is used. Use your experience to dictate tube
replacement rather than wait for a tube failure and possible lost air time . Because of its
outstanding component accessibility the Model 707 is easy to maintain . Use the servicing
aids that are provided as a part of the transmitter. Note the flags on the overload re l ays
(K- 8, K-9, K-10) when trouble is being experienced. Re-check your tuning procedures.
Make sure that you tune the final tank circuit beginning with the vacuum var i able capacitor
in its maximum capac i ty position (counterclockwise) . Don 't overlook the simple solution .
REMOTE CONTROL ·
When operating by remote control the transmitter unit of the remote control system should
be coll.L,ected as foll o ws:
Function
Filament on
Plate on
· Power contr ol .
High/Low power
Remote crystal (Conel rad)
Metering ( plate . voltage)
Meter~g (plate current)
Remote reset
Model 707 Connections
TBl - 8 and 9
TBl -12 and 13*
TBl - 14 (lower)
TBl - 15 (ra i se")
TBl - 16 (common )
XBl - 16 and 1 7.
TBl - 16 and 18
TBl -4 and 5
TBl -6 and 7
TBl -11 and 12*
* With some remote control systems outboard latching relays _ may be required in these
positions. For help in any rem o te e:ontrol problems, contact the Bauer factory stating
680215. 2
Page 11
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the make and model of remote'" control system to be used. Shown below is a Rust,
Model 108-4A latching relay unit as it would be used with the Bauer Model 707 transmitter.
WhE;n the "plate on" function is initiated a circuit is completed ( through the operate relay
contacts) between TBl-12 and 13 , allowing plate voltage to come on. (Toggle switch S2
on the transmitter is always left on when the transmitter is to be run by remote control.)
To turn off the plate voltage or to reset the overload relay K3, · the "p late off/reset"
function is initiated. This will break the connection between TBl -12 and 13 (removing !;)late
voltage) and simultaneously apply 220 volts AC to reset K3. It is important in all remote
control systems to duplicate the functions of S3 and S4 as closely as possible. When re-
setting the overload relay plate voltage must be automatically removed by the control
system. The . reset voltage applied to K3 can be continuous or momentary . depending
~pon the type of latching relay used.
r-- ---- - - ,
I ..,.._1 ------.
to
TBl-12
2
· I ...__I__,
I
I
I
I RELEASE
I
I
L_
3
to
TBl-11
OPERATE I
_ _ _. _ _J
4
to
TBl-13 .
6 7
from
Plate On ·
functico
I •
10
common from
Plate Off/ Res.::t
function ·
Figure 3. · Latching Relay Unit - Rust Model 108-4A.
680215.2
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GENERAL SERVICE INFORMATION
Safety Notice
WARNING
Voltages used for the operation of th is equipment are dangerous to human
, life.
This instruction book is written for the general guidance of maintenance and service
personnel who a~ familiar with and aware of the dangers of handling electric and elec-
tronic circuits. Standard safety precautions should be followed when servicing this
equipment. The servicing of this equipment by' inadequately trained or i nexperienced
personnel involves risks to such personnel and to the equipment for which the manu -
facturer cannot accept responsibility. Personnel servicing this equipment should famil -
- ,·
iarize themselves with first aid tre·atment for electrical burns and electrical shock.
Production Changes
Frpm time to time it becomes necessary to make changes in the equipment described in
this book. Such changes are made to improve performance or meet component changes.
PriQ.r to reprinting an addenda sheet will be provided in the front of this instruction book
describing the changes and the necessary corrections for this book,;..., This information is
provided as a ser.vicing aid 3:.nd should not be used to modify earlier equipments exc _ ept
under specific instructions.
. Replacement Parts
The parts lis ... r contained in this book includes all principal replaceme_nt parts. The symbol
. numbers are the same as those used on the main schematic. Wherever possible the rnanu-
facturer 's name and type are given to aid you in securing local replacement of any of the
parts used in this equipment. The majority of the parts useci in this equipment are avail -
able right o'ff the,shelves of the better electronic parts houses . . You are encouraged to
use these so-urces of supply. When necessary to order from the factory please give t..11e
symbol, equipmenu:ype· or model and part number. Orders should be sent to Granger
Associate~, Bauer Broadcast Products Divi~ion, 1601 California· Avenue, Palo Alto,
California 94301 USA. .
680215.2
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WARRANTY
SPARTA ELECTRONIC CORPORATION warrants to the _purchaser of SPARTA
Electronic Products that any part thereof, which proves to be defective
within one year from the date of shipment, will be repaired or replaced
free of charge if returned to _ the factory prepai d. All ret~rns must be
specifically authorized by the factory prior to shipment.
SPARTA reserves the right to make chang e s in design and improvements
upon its products without assuming any obligation to install the same upon
any of its products theretofore manufactured.
High voltage transformers, modulation transformers, reactors and filter
chokes carry an extended warranty of 50% of the replacement cost being
allowed should failure occur during the second year. Electron tubes and
silicon rectifiers bear only the warranty of the manufacturer thereof in
effect at the time of shipment to Purchaser.
Accessories supplied by, but not manufactured by SPARTA ELECTRONIC
CORPORATION,
shall carry only such manufacturer ' s standard warranty
and are specifically excluded from SPARTA ELECTRONIC CORPORATION' s
warranty.
This warranty is expressly in lieu of all other warranties express or implied
and does not apply to normal wear and tear or damage resulting from shipment,
misuse, unauthorized modifications, or any other modifications, or any other
cause or condition except normal usage. Replacement parts . supplied under
this warranty carry only the unexpired portion of the original warranty •
8/3/70

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Tabl
e 2.
Typical
Transmitter
Performance
Data,
Bauer
Model
707.
Circuit
I
Aud
-
io
Plate
Oscillator
Plate
Driver
Plate
Fi
nal
Grid
~
Fin
al
Sc
reen
Modulator
Plates
Final
Plate
Volt
age
Fin
al Plate and Sc
reen
R.
F.
Output
Meter
Readings
250
Watts
500
Watts
1000
Watts
0%Mo
d.
100%Mod. 0%Mod.
100
%Mod.
0% Mod. 100%Mod.
4-5
ma
4-5
ma
4-5
ma
4-5
ma
4-5
ma
4-5
ma
I
10-12
ma
10-12
ma
10-12
ma
10-12
ma
10-12
ma
10-12
ma
8-14
ma
8-14
ma
14-18
ma
14-18
ma
16-24
ma
16-2
4
ma
11-13
ma
11-13
ma
14-16
ma
14-16
ma
18-20
ma
· 1
8-20
ma
50-58 ma
,/
24-29
ma
24-29
ma
34-38
ma
34-38
ma
50
-58
ma
• 380-420
ma
,r
120
ma
190-210
ma
115
ma
290-3
15
ma
.
llOma
1450-1550 V 2050-:2150 V
1450-1550 V 2050-2150 V 2900-3100 V _2900-3100 V
220-260
ma
220-2
60
ma
320-360
ma
320-360
ma
480-560
ma
480-560
ma
2.
28
amps
2.
78
amps
3.
18
amps
3.
25
amps
4.56
amps
·
5.
56
amps
.
·-
·
--
-·-· -· -..
TYI!_ic
al
Performance
Audio
input
lev
el,
1000
cp
s,
100%
mod.,
+
10
dbm
No
i
se
,
-58
db below 100%
modulation
Distortion,
measured
at
95%
modulation,
1000
watts
50 c
ps
,
1.4
%
1000
cps,
0.
6% 100
cps,
0. 9%
5000
cps,
0.
9%
400 c
ps
,
0.
7%
7500
cps,
1.
2%
R
esponse
at
1000
watts
(variation
from
1000 c
ps,
30
cp
s ,
-1.0
db
50
cps,
0.0
db
400cps,
O
,Odb
lOOOcps,
O.Odb
5000
cps,
+
0.
2 db 7500
cps,
+
O.
3 db
95%
modul
at
ion)
100
cps,
0.
0 db
3000
cps,
0.
0 db
10
,000
cps,
+
0.1
db .
Effici
ency
70-75% D
ummy
Resistance
48
ohms
')