McMartin TR-66A Manual

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1-fCMartin industries. inc.
• I
I
i
INSTALLATlCN AND SERVICE MANUAL
TR-66A
SCA TRANSISTORIZED
MULTIPLEX RECEIVER

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TABLE OF CONTENTS
UNPACK ING . . . . . • . . . . . . • . . . . . • 1
WARRA.NT'l .••
SPECIFICATIONS •
SPECIAL FEATURES .
. . . .. 1
• • • 2
• • 4
GENERAL DESCRIPTION ...•.........• S
INSTALLATION PROCEDURE .......•..•.• 6
FIELD ADJUSTMENTS
TROUBLESHOOTING ..
• • • 7
TRANSISTOR AND DIODE COMPLEMENT.
SCHEMATICS
• 11
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UNPACKING
Remove
the
receiver
from
the
carton
and
examine
it
for
signs
of
external
physical
damage.
Remove
the
top
cover
by
loosening
the
four
screws
at
the
sides.
Examine
transistors,
crystal
and
etc.,
to
see
that
they
are
properly
seated
in
their
sockets.
If
any damage
is
noticed,
ilIDllediately
notify
the
shipping
agency
and
advise
McMartin
Industries,
Inc.
of
such
action.
Contents
of
Carton:
l McMartin
Multiplex
Receiver
l
Instruction
Manual
l Cover Nut
(for
MN-MX
Switch)
WARRANTY'
McMARTIN
Broadcast
and Audio
Products
are
warranted
to
be
free
from
defects
in
workmanship
FOREVER.
At
our
discretion,
we
will
exchange
or
repair
any
defective
unit
or
components,
at
any
time,
without
charge.
Material
and components
are
guaranteed
for
a
period
of
ninety
days
from
the
date
of
original
purchase
.
Return
authorization
should
be
obtained
and
transportation
char~es
must
be
prepaid
on
equipment
returned
for
warranty
service.
This
warranty
does
not
extend
to
any•of
our
products
which
have
been
subjected
to
misuse,
neglect,
accidents,
incorrect
wiring
not
our
own,
improper
installation,
or
to
uni
ts
that
have
been
used
in
violation
of
the
instructions
furnished
by
us;
nor
to
units
that
have
been
altered
outside
our
factory.
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'
i ..
Main Channel
Range
Sensitivity
Selectivity
Capture Ratio
RF Input Antenna
Distortion
Subchannel
Range
Sensitivity
Selectivity
De-emphasis
Cross Talk
Frequency response
Distortion
Hum and noise
General
Outputs
SPEC;[FICATIONS
88-108 mHz, crystal controlled ·
1
microvolt for 30 db of quieting, complete
limiting at 3 microvolts
Fixed 250 kHz at 3 db points, 553 kHz at 50 db
points
Better than 1.25 db
50-72 ohms (solderless coax connector)
Less than 0.5% at 1007. modulation (400 Hz)
41, 42, 65 or 67 kHz at+ 6 kHz deviation -
other frequencies special order. (Must specify
frequency when ordering.)
(20% Inj.)
(10'1.. Inj .)
5 microvolt/45 db quieting
5 microvolt/30 db quieting
~ 7.5 kHz at 3 db points
150 microsecond standard, 75 microsecond on
special request
Main to SCA
SCA to SCA
Stereo to SCA
-55 db
-55 db
-55 db
30-8,000 Hz~ 2 db at 150 microsecond de-emphasis
Less than 1.07. + 6 kHz Dev., 400 Hz.
G~•ater . than 60 db below full output
Main and sub-channel switched l.OV at 600 ohms
unbalanced (phone jack). Optional: Balanced
25 and 70.7 volt (terminal board) with LT-lOA
or LT-20 plug-in amp.
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Front
Panel
Controls
Rear
Chassis
Under
Chassis
Power
Supply
Dimensions
and
finish
Shipping
weight
Pilot
Light
Lamp
SPECIFICATIONS
(continued)
Main/sub-selector
switch,
volume
control,
power
ON-OFF
AC
convenience
outlet
(unswitched)
Antenna
connector
Antenna
B+
switch
Fuse
holder
Mike preamp
input
(4
pin
Jones
plug)
Adjustable
automatic
main
channel
muting
105-120V
AC
50/60
Hz
fused
at
0.5
amp;
normally
5
watts,
with
LT-lOA -
15
watts,
with
LT-20 -
22
watts.
11"
wide
x 4
1/2"
high
x 8
3/4"
overall
depth,
gray
cover
and
brushed
chassis
7
lbs.
Neon
assembly
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SPECIAL
FEATURES
*
The
elimination
of
tunable
IF
transformers.
The
IF
transformers
have
been
replac~
by a
single
10.7
mHz
solid
state
filter.
The
bandwidth
remains
constant
at
all
signal
levels
and
is
phase
linear
over
220 kHz.
*
All
transistors
operate
at
less
than
501.
of
their
rated
dissipation
for
increased
long
life
through
cool
operation.
* The
sub-carrier
uses
a
phase
linear
bandpass
filter
with
steep
sided
skirts
for
rejection
of
stereo
and
second
sub-carrier.
*
Noise
rejection
is
excellent
due
to
the
elimination
of
time
constants
in
the
limiters.
*
A
pulse
counting
detector
is
used
eliminating
drift
and
the
necessity
for
tuning.
Near
perfect
linearity
is
also
obtained.
*
Convenient
test
points
for
easy
aligmnent
of
the
RF
section.
*
Integrated
circuitry
is
used
in
both
the
main
channel
and
sub-channel
limiter
amplifiers.
*
RF
shielding
meets
FCC
requirements.
*
Unit
is
supplied
with
an
RF
solderless
connector,
both
male
and
female
for
72
ohm
coax.
*
There
is
a
front
panel
switch
for
MN
(main)
and
MX
(sub-channel).
This
switch
simplifies
servicing
and
enables
a
customer
to
switch
to
the
main
channel
for
special
announcements,
such
as
historical
events
or
local
distress
notices.
A
cover
nut
is
supplied
with
all
units
and
can
replace
the
knob
if
it
is
desired
that
the
customer
be
prevented
from
using
the
switch.
*
1"'10
plug-in
amplifiers
are
available:
LT-lOA,
5-watt
amplifier;
LT-20,
12-watt
amplifier.
A
socket
is
provided
for
these
plug-in
amplifiers
and
all
wiring
is
·
rincorporated
1n
the
receiver.
The
25
and
70.7
volt
outputs
are
available
on a
terminal
strip
on
the
rear
of
the
chassis.
* A
plug-in
mike preamp
is
also
available
for
connecting
a mike
to
either
the
tuner
or
tuner-amplifier
combination.
This
preamp
employs
solid
state
switching
to
mute
music
when a
push-to-talk
mike
is
used.
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GENERAL DESCRIPTION
The TR-66A multiplex receiver is desi g ned for continuous duty r_ eception
of commercial FM/SCA multiplex programming.
The TR-ooA is built on a modular construction basis utilizing five glass
epoxy printed circuit boards .. These consist of an RF amplifier, IF amplifier
and demodulator, subchannel demodulator, dual gate squelch and audio
amplifier, and power su pply.
The RF amplifier board uses two silicon field effect transistors (FET's)
in a cascade configuration for excellent AGC with minimum cross-modulation
The local oscillator is crystal controlled .• k~silicon bipolar transistor
is used for a mixer which is suitable for driving the low impedance solid
state 10.7 mHz filter. A 10.7 mHz IF trap is used in the mixer input to
improve the conversion gain.
The main channel IF board consists of two high gain, wide band integrated
circuits (IC's), an AGC and squelch circuit, pulse counting demodulator
and an audio amplifier.
The subchannel demodulator uses 1 integrated circuit (IC) for an amplifier
and limiter, a pulse counting detector, a squelch voltage amplifier and a
one stage audio amplifier. ·
The
dual gate squelch board and audio amplifier consists of a main and
subchannel gate which requires both main and subchannel squelch voltage for
operation. Positive squelch will occur in case of main channel failure.
The audio amplifier has an unbalanced low impedance output.
Two plug-in audio modules are available to transform the TR-66A into a
tuner-amplifier combination. A mike preamp is also available for the
TR-66A.
The power
supply board has a regulated 13V output for operating the receiver
and the optional plug-in mike preamp, and an unregulated 36V output to operate
either of the two optional plug-in power amplifiers.
Straight line design with test points make the TR-66A a very easy unit to
- align. There are no tuned circuits past the RF section. With no LC tuned
circuits in the IF, the problem ot drift need not be considered.
The main channel is crystal controlled to receive an FM frequency between
88 and 108 rnHz. An extremely well regulated power supply, utilizing
electronic control, assures circuit stability. The subcarrier is fixed
at+ 6 kHz deviation and may be ordered on 41, 42, 65 or 67 kHz. Other
subcarrier frequencies are available upon special request. The frequency
must be specified when ordering.
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INSTALLATION PROCEDURE
Inspection
Upon receipt of your TR-66A remove it from the packing material and
inspect carefully for any damage caused in transit due to rough handling
or vibration. If damage is found, notify the shipping agency and advise
McMartin Industries, Inc. of such action.
Receiver Location
Sufficient space should be allowed for proper circulation of air to aid
in the cooling of the unit. Keyhole slots are provided in all bottom
plates to facilitate mounting the receiver on a wall. This is important
in order to increase air circulation and also to prevent use of the
recaiver as a "shelf" for paper, books, etc. It will also eliminate the
possibility of your customer moving the receiver and shorting or breaking
connecting wires. The receiver should be located as near to the entrance
of the antenna coaxial cable as possible.
Antenna
A properly selected and installed antenna is one of the most important
factors for satisfactory multiplex reception. Good directional char-
ac . teristics are very important in the reduction of "multipath" (cross talk)
reception and only proper antenna installation can eliminate this. This
condition is most c011111on in large metropolitan areas and mountainous
country. High gain antennas normally have the best directional pattern
and although signal strengcb may be high at a given location, it may still
be necessary to use this type to eliminate multipath. The antenna should
be o~iented for a combination of best signal and lowest multipath.
For all installations we recormnend the use of either a McMartin outside
(A-·72-SF) 3 or S element, 72 ohm, cut-to-frequency directional antenna or
indoor (A-72PA) transistor, fixed-frequency antenna. For proper location
and orientation of the antenna ., we recommend using the McMartin TX-200
Field Strength Meter.
Antenna Connection
An RF coaxial receptacle is provided on the rear of the chassis for the
re.commended outside antenna. A solderless connector plug is furnished with
the receiver for connection to the cable. The coaxial lead-in eliminates
receiving ignition and other man-made noises by the antenna line.
The reconwne~ded input impedance is 72 ohms, however, a 50 ohm impedance
may be used with little mismatch. Additional antenna connector plugs
may be obtained from McMartin Industries by ordering part #173009.
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FIELD
ADJUSTMENTS
A
considerable
aroount
of
time
has
been
spent
aligning
your
receiver
to
your
exact
center
frequency.
Normally,
the
only
field
alignment
that
should
be
necessary
is
to
peak
the
antenna
coil
to
match
the
receiver
to
your
antenna.
The
following
procedure
can
be
used
if
a
frequency
change
is
required
or
for
touch
up
alignment
under
field
conditions.
It
should
be
noted
that
it
is
very
easy
to
peak
the
RF
section
to
an
adjacent
station
so
extreme
care
should
be
taken
in
the
RF
alignment.
Local
Oscillator
and
RF
Alignment.
1.
Reroove
only
the
receiver
top
co
v
er.
CAUTION:
Do
not
remove
the
bottom
plate
in
high
RF
signal
areas.
2.
Connect
a
volt
ohmmeter
(20k
ohm/volt
VOM)
,
or
preferably
a
VTVM
to
test
point
11
AH
(TP-A)
and
ground.
(-3.0
VDC
scale).
3.
Turn
the
oscillator
sl
ug
counterclockwise
(out)
as
far
as
it
will
go.
4.
Insert
the
proper
crystal
into
the
crystal
socket.
Crystal
frequency=
Operate
Freque
ncy
-10o7
mHz
2
S.
Slowly
turn
the
oscillator
slug
clockwise
(in)
until
the
ne~ative
voltage
rises
abr~pt
ly
,
in
di
cating
oscillation.
Continue
clockwise
until
the
voltage
drops
1/10
to
2/10
of
a
volt
below
the
peak
to
insure
positive
starting.
T
his
voltage
should
be
at
lea
st
one
volt
de
~ith
a 20 k
chm/volt
VOM.
6.
~E
::
h
the
meter
on
TP-A,,
tun~
the
do
ubler
coil
fo
r a
sharp
d
ip.
Min
imum
meter
reading
with
a
rap
id
voltage
r
i=~
when
the
core
is
turned
right
or
left
indicat
es
proper
tuni~
g.
7.
Connect
an
antenna
to
the
TR-~
6~.
8.
Connect
a
VTVM
to
TP-C
or
TP-
B
1
-3
.,
0
VDC
scale)
(
see
::ote
) .
9.
Tune
the
mixer
coil
for
maximum
negative
voltage
readin
g.
If
two
peaks
are
noted
,
tune
tc
the
peak
producing
the
highest
voltage.
10.
With
a
VTVM
connected
to
TP-C
or
TP-B,
tune
the
RF
coi_
for
maximum
negative
voltage.
'
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FIELD
ADJUS'IMENTS
(Continued)
11.
With
a
VTVM
connected
to
TP-C
or
TP-B,
tune
the
doubler
coil
for
maximum
negative
voltage.
12.
With
the
VTVM
connected
to
TP-C
or
TP-B,
tune
the
antenna
coil
for
maximum
negative
voltage.
13.
Repeat
steps
8,
9,
10,
11,
and
12,
until
no
further
improvement
can
be
made.
NOTE:
Since
there
are
no
tuned
circuits
in
the
rest
of
the
'ra-66A
you
may
listen
for
quality
on
both
the
main
channel
and
the
SCA
multiplex
channel.
Test
point
"C"
should
be
used
in
areas
where
there
is
more
than
SO
microvolts
of
signal
available.
In
strong
signal
areas
the
signal
must
be
attenuated
during
alignment
to
minimize
the
AGC
action
of
the
front
end,
especially
in
a
metropolitan
area
with
a
strong
adjacent
or
alternate
channel.
If
the
TR-66A
is
installed
in
a
fringe
area,
and
no
voltage
is
present
at
test
point
"C",
test
point
"B"
should
be
used
for
alignment.
(In
very
weak
signal
areas
the
voltage
may
be
positive
and
the
receiver
should
be
tuned
for
minimum
positive
or
a
negative
going
voltage)
.
For
steps
5,
6,
8,
9,
10,
11,
and
12,
it
is
PREFERABLE
to
USE
a
VTVM.
This
completes
the
oscillator
and
RF
align~ent.
*
On
units
with
screw
driver
adjusted
oscillator
slug
-
steps
3
and
5
should
be
as
follows:
3.
Turn
the
oscillator
slug
clockwise
(in)
as
far
as
it
will
go
.
5.
Slowly
turn
the
oscillator
slug
counterclockwise
(out)
until
the
negative
voltage
rises
abruptly,
indicating
oscillation.
Continue
counterclockwise
until
the
voltage
drops
l/10
to
2/10
of
a
volt
below
the
·
p,eak.
~
This
voltage
should
be
at
least
-1.5
volts
DC
with
a
20
K
VO~.
De-Emphasis
The
TR-66A
subchannel
has
a
standard
de-emphasis
of
150
microseconds.
To
change
this
de-emphasis
to
75
microseconds,
change
capacitor
C-12 on
the
subchannel
demodulator
board
from
.001
mfd
to
.00075 mfd.
-8-