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PRICE $1.2 6
STEREO
MR 73
FM-AM TUNER
SOLID STATE
CONTENTS
IF YOU'RE IN A HURRY
5
PERFORMANCE CHARTS
6
SPECIFICATIONS
7
INSTALLATION
FRONT PANEL INFORMATION
8-9
10-11
BACK PANEL INFORMATION
12
TYPICAL HOOKUP
13
CONNECTING
14
LISTENING
15
GUARANTEE
16
Your purchase of a Mclntosh instrument
shows that you are a careful discriminating buyer. One who is interested in quality
performance, quality engineering, quality
manufacturing, and long trouble-free
equipment life. You can protect your investment by spending a few minutes reading this owner's manual.
When you bought a Mclntosh, you bought
countless hours of musical pleasure and
superior performance. Enjoy it!
1
FM-AM TUNER
The Mclntosh "will to perfection" requires that we probe
constantly into the unknown to bring the performance of our
electronic equipment closer to perfection than ever before.
This requires a constant and relentless search for low noise,
broad band conservative design with an ever lower distortion
factor. This is not required of ordinary equipment of average
designs. It is, for us, a costly but worthwhile scientific and
engineering effort. Our continuing research benefits our customers with the almost complete lack of obsolescence and
the most reliable equipment ever made. It also means the
lowest long-range cost to you. Nearly all of the Mclntosh
equipment ever made is still in use, or useable, though it
may have been made twenty years ago.
2-4
MR 73
STEREO
TECHNICAL DESCRIPTION
2
SOLID STATE
INTRODUCTION
INTRODUCTION
TECHNICAL DESCRIPTION
The Mclntosh MR 73 is a precision engineered, highly sensitive
solid state AM-FM tuner.
The research staff of Mclntosh Laboratory, using the latest technology in solid state physics, has developed many circuit advances:
- Phase linear crystal shaped IF amplifiers
- Integrated Circuits that are the equivalent of 16 transistors,
3 zener diodes, 5 diodes, and 23 resistors
- Special multiplex (stereo) detecting circuits that eliminate
critical adjustments
- Ultrasonic muting for complete silence between stations while
tuning
- Automatic stereo-mono switching that is "clickless" and completely electronic
- Visual multipath indicator to help avoid multipath distortion
showing as a visual indicator of correct antenna direction for
minimum multipath reception.
- New D'Arsonval movement meters of increased sensitivity
which do not need zero setting adjustments.
- A new computer designed filter to reduce noise from stations
broadcasting subcarrier auxiliary music services. No other
tuner uses such a filter.
F.M. SECTION: This is divided into two separate modular sections:
A. The 100 mHz Radio Frequency {RF) Section. This section
houses the complete FM-RF front-end and part of the AM-RF circuits. A special, four section, variable tuning capacitor provides a
high degree of RF selectivity and excellent spurious response rejection. The problem of image rejection has been greatly reduced in the
RF section of the MR 73.
The two stage parallel-fed-cascode junction field effect transistor
(JFET) RF amplifier gives better sensitivity and higher gain than
conventional one-stage amplifiers. The use of JFET's helps to further
reduce the problem of front end overload in strong signal areas.
A mixer using a JFET has been designed for high sensitivity and
freedom from overload. Low temperature coefficient components
have been designed into the FM local oscillator to prevent frequency drift. The frequency stability inherent in the local oscillator
makes automatic frequency control (AFC) unnecessary. The rate of
drift of the local oscillator is less than ten parts per million per
degree centigrade.
Both the FM and AM-RF front ends have been designed in the
same completely encased metal modules. This design gives protection against radiation or interference. The RF circuits of the MR 73
exceed the FCC requirements for suppression of oscillator radiation.
The MR 73 has antenna connections for either 300 ohm twin lead
transmission line or 75 ohm coaxial cable. The normal input impedance of the first RF amplifier is 75 ohms. Impedance match to
300 ohms is provided by a Mclntosh designed balun transformer
which has negligible losses. Connections for a 300 ohm line are
made with new push type terminals. No tools are required. A type F
male connector is furnished for 75 ohm coaxial cable.
For greater signal transfer and lower distortion, a special matching transformer has been designed to interface the FM-RF to the
FM-IF amplifier. This matching transformer considerably enhances
the linear phase characteristics of the IF amplifier.
B. The FM-IF and Detector Section. The FM-IF and Detector design required extended engineering time and testing and uses the
latest concepts in integrated circuits and crystal filters. The FM-IF
consists of two integrated circuits and two phase linear crystal
filters. They combine to give a total gain of over 120 dB (the signal
is amplified to over 1,000,000 times its original level). The response
Exclusive Mclntosh PANLOC is used for installation. The PANLOC
system gives you absolute ease of installation, operation, and maintenance.
PANLOC is the first professional installation technique to be used
on stereo instruments.
In the PANLOC system a metal shelf is mounted first. The tuner
slides into position on this shelf. Depressing the front panel PANLOC buttons, locks the tuner firmly into position against the mounting panel.
Once you have enjoyed the outstanding performance of the
MR 73, you will understand why Mclntosh products have earned
their reputation as "THE BEST." Your Mclntosh MR 73 tuner will
give you years of the finest possible reception, and will be a valued
part of your home music system.
2
curve has a nearly flat top with linear phase characteristics. The
skirts of the response curve are very steep. The maximum width is
240 kHz at -3.0dB and 400 kHz at -60dB. The response curve is
symmetrical each side of the center frequency. The crystal filters are
permanently sealed and do not require adjusting. The IF cannot
drift nor vibrate out of adjustment.
Each of the two integrated circuits used in the FM-IF of the MR 73
contain 16 transistors, 3 zener diodes, 5 diodes and 23 resistors, all
on a single monolithic silicon chip.
The exceptionally high gain of the two integrated circuits assumes
"hard limiting" at very low levels of input signals.
A "phase" or "Foster Seeley" discriminator has been designed
to complement the integrated circuit IF section. The IF section has
exceptionally high gain and hard limiting characteristics, yet the
capture ratio is quite low. The detected output signal of the discriminator is extremely low in distortion content.
De-emphasis of the discriminator output restores the frequency
amplitude characteristics to the same level they were before transmission.
C. FM Stereo Multiplex Section. Mclntosh Laboratory has developed a special detecting circuit in the multiplex section. A particular advantage of this circuit is the elimination of the critical
adjustments necessary with commonly used matrixing circuits. The
circuit detects the L-R sidebands, then automatically matrixes the
recovered information with the L + R main carrier signal. This yields
the left and right program output with maximum separation.
The 19kHz pilot signal is filtered from the composite stereo input
signal, amplified by a special limiting amplifier, doubled to the 38kHz
carrier frequency, and then amplified again by a limiting amplifier.
The composite signal minus the 19kHz pilot is combined with the
38kHz carrier signal. The new combination of signals is fed to the
special detector circuit mentioned above. Balanced full wave detectors are used to cancel the 38kHz components in the output.
The SCA (Subsidiary Communication Authorization) signal must
be removed from the composite output. This is accomplished by the
use of a new "Image Parameter" band elimination filter that has
been computer designed. The SCA filter rejects SCA signals without
impairing stereo performance.
FM muting in the MR 73 operates by detecting ultra-sonic noise
which is present when tuning between stations or when receiving
a weak station. The muting circuit can be activated or defeated by
the use of the muting switch on the front panel. The level of muting
desired can be adjusted by the muting level control on the top panel.
Varying the muting control adjusts the threshold at which the muting
takes effect.
When the 19 kHz carrier of a stereo signal is received, the automatic FM stereo switching circuit activates the multiplex decoding
circuit. This lights the stereo indicator. The circuit switching is all
done electronically with no clicks. The automatic stereo switching
can be defeated by turning the mode selector switch to FM MONO.
(In this position the stereo indicator will still light to indicate the
presence of a stereo signal.) On monophonic transmissions the
stereo switching is inactive at all times, assuring a greater signal to
noise ratio. The stereo switching circuit has been designed so that
noise will not activate it.
AM SECTION:
The "state of the art" in electronic technology has been incorporated by Mclntosh into the MR 73 with the use of metal oxide silicon
field effect transistors (MOSFET's) in the AM section. An AM-RF
amplifier circuit includes a three section variable tuning capacitor
in the metal enclosed shielded module, which also houses the
FM-RF front end. The AM-RF amplifier uses a dual-insulated gate
MOSFET to obtain more overload protection against strong local
stations than can be obtained with conventional bipolar transistors.
The AM-RF mixer is also a dual-insulated gate MOSFET. The use
of MOSFET's in the RF amplifier and mixer provides the MR 73 with
very little cross modulation (spurious response) and the image rejection is very good.
Three double tuned IF transformers are used to obtain a high
degree of selectivity yet still allow good AM fidelity. A 10kHz whistle
filter has been incorporated at the output of the AM detector. Its
3
purpose is to supress hetrodyning that occurs between adjacent
AM carriers.
To increase the "pulling power" of the AM section of the MR 73,
connect an external antenna at the rear apron of the unit by using
a push connector. An internal transformer matches the external antenna to the input impedance of the AM front end. An optional highly
sensitive loop stick antenna is also provided for local or strong
stations. A switch on the back pane! selects either loopstick or
external antenna.
An AM sensitivity switch has been provided to decrease both the
gain of the RF amplifier and the noise between stations.
AUDIO PREAMPLIFIER SECTION:
An audio amplifier has been incorporated in the MR 73. It increases the audio level from the AM or FM multiplex outputs to a
level sufficient to drive a preamplifier or other accessory equipment.
The audio amplifier consists of 2 separate amplifiers, each amplifier
having three transistors. The design uses considerable negative
feedback. Negative feedback helps to achieve low distortion, wide
frequency response, and unexcelled stability. Each audio amplifier
has two low impedance outputs. One is a fixed output set at 2.5
volts. The second output is variable by the volume control on the
front panel.
By cross-coupling a small portion of one channel into the other
in the audio amplifier, the residual alternate channel information
can be cancelled, thereby further increasing the stereo channel
separation.
Also included in the audio section is a STEREO FILTER switch.
With the STEREO FILTER turned on and weak stations are being
received, stereo noise is reduced, but still allows ample stereo
listening performance.
POWER SUPPLY
Special design attention has been given to the power supply
section of the MR 73. Two separate rectifier circuits are used in
the MR 73.
4
The 16 volt regulator is the power heart of the MR 73. All signal
stages throughout the unit are powered from this regulator. The
16 volt regulator is very elaborate in design, using a specially selected transistor and associated circuit. The regulator uses electronic filtering to insure the lowest possible background hum level,
maximum stability and extremely good regulation.
A half wave rectifier and filter, supply the DC high voltage needed
for the anode of the multipath indicator. The second power supply
is a full wave rectifier which supplies DC to the multiplex indicator
and to the voltage regulator.
MODE SELECTOR— Select from AM broadcast, stereo FM broadcast, or
mono FM without automatic stereo/mono switching.
STEREO FILTER— Reduces noise on weak FM stereo broadcasts.
MUTING—Eliminates the usual noise between FM stations.
VOLUME/OFF—Turns the AC to the tuner on or off and adjusts volume to
desired level.
IF YOU'RE IN A HURRY
STEREO INDICATOR—Lights when station is transmitting 19 kHz carrier
for stereo broadcast.
MULTIPATH INDICATOR— Rotate antenna until electron ray edges are
steady.
SIGNAL STRENGTH—Tune for maximum reading with a steady multipath
indicator.
FM TUNING— Tune FM until the indicator is in the black area in the center
of the meter face.
5
FM STATION LOG
STATION
6
DIAL
FREQ.
LOG
SCALE
LOCATION
CITY, STATE
ANTENNA
DIRECTION
REMARKS
MONO—STEREO-TIME-DATE
SPECIFICATIONS
FM
SCA FILTER: 50 dB down at 67 kHz to 74 kHz, 275
dB per octave slope.
USEABLE SENSITIVITY: 2.5 microvolts at 100%
modulation (±75 kHz deviation) for less than 3%
total noise and harmonic distortion in accordance
with IHF standards.
AUTOMATIC MONO-STEREO SWITCH: Mclntosh developed; all electronic automatic mono-stereo switching circuit.
AUDIO FREQUENCY RESPONSE: Flat from 20 Hz
to 20 kHZ with standard de-emphasis and 19 kHz
pilot filter.
HARMONIC DISTORTION: Mono: Less than 0.3% at
100% modulation ±75 kHz deviation. Stereo: Less
than 0.7%.
CAPTURE RATIO: Better than 1.5% dB at 100%
modulation.
MUTING: AF injected ultrasonic muting: at least
60 dB noise reduction between stations.
OSCILLATOR DRIFT: Less than 25 kHz.
IMAGE REJECTION: Better than 80 dB at 90 MHz;
better than 70 dB at 100 MHz.
SEMICONDUCTOR COMPLEMENT: 22 diodes, 24
Transistors, 2 Integrated Circuits, 1 Indicator Tube.
AM
SENSITIVITY: Better than 12 microvolts at 1000 kHz
(using the external antenna input).
FREQUENCY RESPONSE: Down 6 dB at 5 kHz.
HARMONIC DISTORTION: Less than 1% at 30%
modulation.
SELECTIVITY: - 3 0 dB at 10 kHz.
IMAGE REJECTION: 60 dB or greater at 1000 kHz.
SIGNAL TO NOISE RATIO: Better than 55 dB.
POWER CONSUMPTION: 20 watts, 105 to 125 volts,
50 to 60 Hz.
HUM: Better than 70 dB below 100% modulation.
OUTPUT: Approximately 2.5 volts; low impendance.
MECHANICAL SPECIFICATIONS
FM ANTENNA INPUTS: 300 ohms balanced; 75 ohms
unbalanced.
SIZE: Front panel: 16 inches wide by 5 7/16 inches
high; Chassis: 15 inches wide by 13 inches deep,
including PANLOC shelf and back panel connectors;
Knob Clearance: 1½ inches in front of mounting
panel.
AM ANTENNA INPUTS: Built-in loopstick or external
antenna switch selected.
IF: Two ICs and two phase linear crystan filters.
RADIATION: Substantially below FCC requirements.
STEREO SEPARATION: Better than 35 dB at 1 kHz.
STEREO FILTER: Greater than 48 dB suppression of
38 kHz multiplex carrier.
STEREO INDICATOR: Front panel multiplex stereo
light activated by 19 kHz carrier-only.
WEIGHT: 24 pounds net, 36 pounds in shipping
carton.
FINISH: Front panel: Anodized gold and black with
special gold/teal panel nomenclature illumination.
CHASSIS: Chrome and black.
MOUNTING:
PANLOC.
Mclntosh
developed
professional
7
INSTALLATION
Adequate ventilation extends the trouble-free life of electronic instruments. It is generally found that each 10° centigrade (18° F) rise
in temperature reduces the life of electrical insulation by one half.
Adequate ventilation is an inexpensive and effective means of preventing insulation breakdown that results from unnecessarily high
operating temperatures. The direct benefit of adequate ventilation
is longer, trouble-free life.
The suggested minimum space for mounting the MR 73 is 15
inches deep x 17% inches wide x 16 inches high. Always allow for
air flow by either ventilation holes or space next to the bottom of
the amplifier and a means for the warm air to escape at the top.
It is recommended that the MR 73 be mounted in a normal or horizontal position. However, with adequate ventilation the amplifier can
be mounted in any position.
To prepare the MR 73 for installation remove the plastic protective
covering. Turn the MR 73 upside down so that it rests on its top on
the shipping pallet. Remove the four plastic feet fastened to the
bottom of the chassis.
8
Next place the mounting brackets, the parts bag and the mounting
template for easy accessibility.
The professional mounting design eliminates the need for any
shelf or bracket to support the MR 73. It is
completely supported
by its own mounting
brackets.
Position the plastic
mounting template
over the area of the
panel to be cut out for
installation.
The design of the mounting template allows you to position or
locate the cutout from the front or rear of the panel to which the
instrument is to be mounted.
If the cutout is to be located from the rear of the panel, the
following steps will help you.
On the back of the cabinet panel, scribe a vertical centerline
through the exact center of the area in which the cutout is to
be made.
Place the template against the back of the panel and match
the template centerline with the centerline on the cabinet panel.
Make sure that there is at least ¼ inch clearance between the
bottom of the dashed line of the cutout area on the template
and any shelf or brace below the proposed cutout.
Mark the two locating holes ("C" holes on the mounting template).
Drill the two locating holes. Be certain the drill is perpendicular
to the panel.
Now position the template on the front of the panel by aligning
the "C" locating holes on the template with the drill holes.
With the template in place against the cabinet panel, mark the
"A" and " B " drill holes and the four small holes that identify the
corners of the cutout. Join the corner marks with a pencil. The edge
of the template can be used as a straight edge.
IMPORTANT:
CUTOUT.
DRILL THE 6 HOLES BEFORE MAKING THE
Accurately drill the three holes on each side of the cutout area
with a3/16 inch drill.
With the saw on the INSIDE OF THE PENCIL LINES carefully cut
out the rectangular opening.
Secure the mounting strips to the rear of the cabinet panel using
two screws from the hardware package.
plate. The sides of the mounting brackets should match the vertical
dash lines on the template. If necessary, loosen the screws and
push the brackets into alignment and retighten.
Insert the power cord through the opening. Carefully slide the
MR 73 into the opening so the rails on the bottom of the equipment
slide in the track of the mounting brackets. Continue to slide the
instrument in until the front panel is against the cabinet panel.
At the bottom front corners of the PANLOC instruments are the
PANLOC buttons.
Depressing the PANLOC buttons will lock the instrument firmly
in the installation.
Insert the screws in the center holes of the cabinet panel ("B"
holes on the template) and tighten. The screw head should pull
into the wood slightly. (Use two ¾ inch long screws for panels under
½ inch, or two 1¼ inch long screws for panels ½ inch thick and
larger.)
Attach the mounting brackets to the cabinet panel using four
screws.
Place the template over the mounting screws. The mounting
screws should be centered in the "A" and " B " holes on the tem-
Depressing the PANLOC buttons a second time (as with a ballpoint pen) will release the instrument. You can then slide the
instrument forward to the inspection-adjustment position.
Depressing the inspection-adjustment position latches will allow
the instrument to be slid completely out of the installation.
VERTICAL INSTALLATION
In the hardware packet are two helical springs. Fasten the springs
to the small flanges at the rear of the PANLOC brackets. The flange
has a notch and a hole to mount the spring. The springs assist in the
removal of vertically mounted PANLOC equipment.
DO NOT USE THE SPRINGS ON HORIZONTALLY MOUNTED EQUIPMENT.
9
FRONT PANEL INFORMATION
TUNING DIAL
The MR 73 has three dial scales:
1. AM —Marked 55 to 160 kHz
2. FM —Marked 88 to 108 MHz
3. Logging scale — Marked 0 to 100
The logging scale can be used to accurately retune any station.
You may find it easier to keep a record of your favorite stations by
use of the logging scale.
will remain steady. The directional antenna is then picking up only
the desired signal and rejecting the reflected multipath signals. In
certain locations it is possible for best reception to occur by picking
up a strong reflected signal rather than the direct signal. Whenever
tuned to a different station, the multipath indicator will show if
multipath distortion is present. Multipath distortion is practically
independent of signal strength.
SIGNAL STRENGTH METER
A small portion of dial pointer has been illuminated to increase
the ease of tuning.
This meter indicates the strength of the received signal from the
antenna. The higher the indication the stronger is the signal.
INDICATORS
FM TUNING METER
The MR 73 has four indicators on the dial panel: STEREO indicator, MULTIPATH indicator, SIGNAL STRENGTH meter, and the
TUNING meter.
STEREO INDICATOR
The STEREO indicator will light when the dial pointer crosses a
station broadcasting the 19 kHz carrier for stereo. The special circuit used will light only when the 19 kHz multiplex carrier is present
in the signal. The indicator will not light on noise pulses or interference.
MULTIPATH INDICATOR
The MULTIPATH indicator is an exclusive Mclntosh development.
The proper use of the MULTIPATH indicator makes it possible to
improve FM reception with precise FM antenna positioning.
An electron ray indicator is used to graphically show multipath
reception. The electron ray indicator operates by movement of
electron beams inside a vacuum tube. The multipath indicator shows
when the antenna is rotated to the correct position for picking up
only the desired signal. Multipath distortion causes the two beams
on the indicator to fluctuate rapidly with the incoming signal. When
the antenna is rotated to the correct position, the indicator beams
10
An FM station is correctly tuned when the indicator is in the black
area of the tuning indicator. The action of the TUNING indicator is
independent of station signal strength.
MODE SELECTOR
Selects any one of three program sources:
AM — Connects the AM tuner section of the MR 73 to the output
jacks.
FM — The FM position provides monophonic FM or FM stereo at
the left and right channel audio output jacks automatically.
With the MODE SELECTOR in the FM position a station
broadcasting monophonic program will be heard in mono.
When the station switches to stereo broadcast, the stereo
indicator will light and the MR 73 will automatically switch
to stereo operation. If mono broadcasting is resumed the
MR 73 will automatically switch to mono.
FM — Mono — Connects the FM tuner sections of the MR 73 to
the output jacks. In this position the automatic stereo
switching is bypassed. The stereo indicator will light when
a station is transmitting stereo. The output will be only
mono.
STEREO FILTER
The STEREO FILTER reduces noise on weak stereo stations.
Turn the switch to the IN position on noisy stereo stations.
FM MUTING
Muting suppresses the background noise and hiss normally heard
between stations. Turn the control to the IN position for muting.
Weak stations that may not override noise and interference are also
suppressed by the muting.
In the OUT position, the muting is turned off. This allows conventional FM tuning with the noise and interference present. Use this
position to tune weak or noisy stations.
VOLUME
This control adjusts the output volume level of the tuner at the
back panel AUDIO OUTPUT jacks marked FRONT PANEL CONTROLLED. The other pair of jacks is marked FIXED OUTPUT. They
are not affected by the volume control. Full tuner output is always
present at the FIXED OUTPUT jacks.
The VOLUME control has been precision tracked throughout the
listening range (0 to —65dB) for accurate stereo balance.
AC ON/OFF
The AC switch is part of the VOLUME control. Turning the VOLUME control totally counterclockwise turns the AC to the MR 73
OFF.
PANLOC BUTTONS
At the bottom of the front corners are the PANLOC buttons. After
a tuner is installed on the PANLOC shelf, depressing the PANLOC
buttons will lock the tuner firmly in position. Depressing the PANLOC buttons a second time (as with a ball-point pen) will release the
tuner. The tuner can then be slid forward to the inspection and
adjustment position. The PANLOC system gives you absolute ease
of installation, operation and maintenance.
SECONDARY CONTROLS
On the top of the chassis behind the front panel are three secondary controls. They are MUTING adjust, AM SENSITIVITY, and
DIAL SCALE INTENSITY.
MUTING
The MR 73 ultrasonic muting circuit suppresses all noise between
stations. It suppresses all weaker stations not strong enough to
override the background noise.
The muting threshold setting determines the strength of the signal
which can be heard with muting in operation. The muting threshold
is carefully adjusted to optimum at the factory using precision test
instruments.
If it is found necessary to adjust the muting threshold, turn the
MUTING ADJ to the RIGHT (clockwise) to lower the muting threshold. This allows weaker noisier stations to be heard at the MUTING
IN setting. Turn the control to the left (counterclockwise) to raise the
muting threshold. This allows only the more powerful stations to be
heard at the MUTING IN setting.
AM SENSITIVITY
When the AM SENSITIVITY switch is in the LOW position the
noise between stations is reduced. The RF gain is not as great in the
low position.
DIAL SCALE INTENSITY
Adjust the brightness of the dial panel lights by means of this
switch on the tuner back panel. Set the switch to BRIGHT for
maximum panel light. Set the switch to DIM for less dial light and
extended lamp life.
11
BACK PANEL INFORMATION
TP1 and TP2
AUDIO OUTPUTS
Test point TP1 and TP2 is provided for tuner circuit alignment.
It is also used in conjunction with the Mclntosh Ml 3, Maximum Performance Indicator.
The left-hand pair of AUDIO OUTPUT jacks provides audio signals
unaffected by the MR 73 front panel VOLUME control. Use these
output jacks to connect the tuner to a stereo control preamplifier
which has its own master volume control.
AC OUTLET
The right hand pair of AUDIO OUTPUT
signal controlled by the MR-73 front panel
these output jacks to connect to external
recorders, or any equipment which requires
control of tuner output volume.
Provides 117 volt AC power up to 350 watts for additional equipment such as turntables, or other equipment. This outlet is not fused.
It turns on and off with the front panel AC switch on the VOLUME
control.
AC POWER
Plug the AC power cord in 105 volt to 125 volt, 50 to 60 Hz power
line. The power used by the MR 73 is 20 watts.
FUSE
A 0.5 AMP fuse protects the tuner circuits. This fuse does not
protect additional equipment connected to the back panel AC outlet.
AM ANT SWITCH
Adjusts the MR 73 circuit to match the particular type of AM antenna used. EXT. position is for a conventional antenna, usually of
the outdoor type, from 50 to 150 feet in length. LOOP position is for
the built-in Ferrite Loopstick.
ANTENNA CONNECTION STRIP
Provides easy push type connectors for an AM antenna, a ground
connection, and a 300 ohm FM antenna.
FM ANTENNA — 7 5 OHM
Provides a type F connector for a 75 ohm unbalanced FM antenna.
12
MR
73
jacks provides audio
VOLUME control. Use
power amplifier, tape
continuous front panel
TYPICAL HOOK UP
FM ANTENNA
AM ANTENNA
POWER AMPLIFIER
PREAMPLIFIER
MR 73
GROUND
(OPTIONAL)
AC LINE
AC LINE
AC LINE
LEFT
SPEAKER
RIGHT SPEAKER
CONNECTING THE MR 73
AUDIO OUTPUTS
Use the FIXED OUTPUT jacks to connect to a conventional control preamplifier which has its own volume control. Full tuner output
is available at all times from the FIXED OUTPUT jacks.
Use the FRONT PANEL CONTROLLED jacks to connect to a
conventional control preamplifier when continuous front panel control of tuner volume is desired. These jacks may be used to connect
to external equipment such as power amplifiers or tape recorders
where control of tuner volume is necessary. There is no difference
in the signal quality or maximum output levels available at each pair
of output jacks.
The output impedance at the outputs is
ohms. Longer cables
than are normally supplied can be used to interconnect the MR 73
with other equipment. The length of the cable is limited by the
capacity of the cable.
Connect the two leads from the dipole to the terminals marked
FM ANT (red). The flexibility of the thin flat wire assembly permits
it to be placed under a rug, tacked behind the stereo . . . or, placed
in any other convenient location. In some cases, it may be necessary
to "position" the antenna for best signal reception. This should be
done before it is permanently located.
CONNECTING AN OUTDOOR 300 OHM FM ANTENNA
An outdoor antenna is recommended for optimum performance
in all areas. In fringe (outlying) areas, best results will be obtained
with a highly directional FM antenna used in conjunction with a
rotator. Rotate the antenna until the best reception is obtained.
Connect the 300 ohm antenna to the terminals marked FM ANT
(red).
CONNECTING A 75 OHM ANTENNA
The total capacity must not exceed 1000 pF. For instance: cables
with a capacity of 25 pF per foot may be 40 feet long; 13.5 pF per
foot cable may be 75 feet long. The input impedance of the other
equipment should be 47,000 ohms or greater.
An unbalanced 75 ohm antenna can be connected to the MR 73
with coaxial cable. A "type F" connector is used to couple the 75
ohm coaxial cable to the MR 73.
CONNECTING AN FM ANTENNA
For most local and moderately distant AM reception the built in
ferrite loopstick antenna may be used. Set the AM ANT. slide switch
on the MR 73 back panel to the LOOP position.
Monophonic installations that are satisfactory on an indoor antenna may require the use of an outdoor antenna for equivalent
stereo results. Satisfactory stereo requires about 10 times as much
signal from the antenna.
One of three antenna systems can be used: (1) the indoor dipole
supplied with the MR 73, (2) an outdoor FM antenna, or (3) a VHF-TV
antenna. In fringe areas best results will probably be obtained with
the use of an outdoor FM antenna. In many areas the indoor dipole
antenna may be satisfactory. The use of a VHF-TV antenna is also
effective in many installations.
CONNECTING AN INDOOR DIPOLE ANTENNA
The flexible folded dipople antenna (300 ohm) is for indoor use in
urban or high strength signal areas.
14
AM BUILT-IN ANTENNA
AM OUTDOOR ANTENNA
For best long distance AM reception, use a copper antenna wire
50 to 150 feet in length. Suspend the wire in a straight line as high
as possible. Attach the wire at each end with suitable glass or
ceramic insulators. Connect a lead-in wire at any convenient point
on the antenna. It is recommended that a lightning arrester be used
with an outdoor AM antenna. The arrester should be well grounded
to a suitable water pipe or copper or aluminum rod sunk into the
ground.
Connect the lead-in wire to the AM ANT. push connector on the
antenna terminal strip on the back panel. Set the AM ANT Slide
Switch to the ANT position.
LISTENING TO THE MR 73
LISTENING TO AM
Turn the MODE SELECTOR switch to AM. Turn the tuning knob
to the desired station. The SIGNAL STRENGTH meter will indicate
the relative strength of the particular AM station being received.
Adjust the VOLUME control to the desired listening level.
LISTENING TO MONOPHONIC FM
Turn the MODE SELECTOR to FM MONO to listen only to monophonic FM.
If you wish to receive monophonic FM and have the MR 73 automatically switch to a stereo broadcast available on the same station
set the MODE SELECTOR to FM.
Turn the STEREO-FILTER to OUT.
LISTENING TO STEREO FM
Turn the MODE SELECTOR to FM.
Turn MUTING to IN.
Turn the tuning knob to the desired station.
The TUNING meter pointer should be in the black area of the
TUNING meter. When the STEREO indicator is lighted, the station
is broadcasting a 19 kHz carrier for stereo. The MR 73 will automatically switch to stereo. If a station is broadcasting monophonic
FM program, the STEREO indicator will remain off and the tuner
will automatically switch to mono.
Adjust the volume control to desired listening level.
If the fixed AUDIO OUTPUT jacks are used, the tuner VOLUME
control will not affect volume.
Turn the tuning knob to the desired station. The correct FM tuning
point is reached when the FM TUNING meter pointer comes to rest
anywhere in the black area of the meter scale. While tuning across
the dial you may notice movement of the tuning meter, without hearing a station. This is caused by a station so weak or distant that
it does not over-ride the background noise. With ultrasonic muting
in operation a noisy station of this type is automatically rejected.
To hear these weaker or distant stations, turn the MUTING switch
to OUT. Usually the listening quality of a station of this type will be
rather poor due to the weak signal and strong background noise.
Rotate the directional antenna for best reception as shown by
the SIGNAL STRENGTH and MULTIPATH indicators.
Adjust the VOLUME control to desired listening level.
15
Your MR-73 FM-AM tuner will give you many years of pleasant and satisfactory performance. If you have any questions concerning operation or
maintenance please contact the dealer from whom you purchased this
instrument or: —
CUSTOMER SERVICE
GUARANTEE
Mclntosh Laboratory Inc.
2 Chambers Street
Binghamton, N. Y. 13903
Our telephone number is
607-723-3512
Mclntosh Laboratory Incorporated guarantees this equipment to be
capable of performance as advertised. We also guarantee the mechanical and electrical workmanship and components of this equipment to be free of defects for a period of 90 days from date of
purchase. This guarantee does not extend to components damaged
by improper use nor does it extend to transportation to and from
the factory.
3 YEAR FACTORY SERVICE CONTRACT
An application for a FREE 3 YEAR FACTORY SERVICE CONTRACT
is included in the pack with this manual. The FREE 3 YEAR FACTORY SERVICE CONTRACT will be issued by Mclntosh Laboratory
upon receipt of the completely filled out application form. The terms
of the contract are:
1. Transportation charges are excluded.
2. This agreement is given to the original purchaser only and is
not transferable.
3. The application for the contract must be filled out completely.
4. The 3 YEAR SERVICE CONTRACT is given to purchasers who
live in the 50 United States or Canada only.
5. This agreement is given only if the equipment is purchased
from a franchised Mclntosh dealer.
6. If the instrument has been modified or damaged by unauthorized repair the contract will be cancelled.
7. To receive free service, the contract must be presented to the
factory authorized service agency, when the equipment is
presented for repair.
If the application is not received at Mclntosh Laboratory, only the
service offered under the standard 90 day guarantee will apply on
this equipment.
16
TAKE ADVANTAGE OF 3 YEARS
OF FREE FACTORY SERVICE
FILL IN THE APPLICA TION NOW
MR 73
McINTOSH LABORATORY INC.
2 CHAMBERS ST., BINGHAMTON, N. Y. 13903
607-723-3512
Design subject to change without notice.
Printed in U.S.A.
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