McIntosh MR-71 Owners manual

FM STEREO

TUNER

CONTENTS

MR 71

TABLE OF CONTENTS

INTRODUCTION
TECHNICAL DESCRIPTION
FRONT PANEL INFORMATION

BACK PANEL INFORMATION

INSTALLATION
CONNECTING

Audio Outputs

Stereophonic FM Multiplex
Monophonic FM
Remote Amplifiers
Off-The-Air Recording
Antenna Connections

OPERATING INSTRUCTIONS

Stereophonic FM Multiplex
Monophonic FM

ADJUSTMENTS

Muting Threshold
Dial Panel Lights
Output Adjust

GUARANTEE

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OWNER'S MANUAL

MR71

THANK YOU

Judging from the stereo equipment you own, you rank high
among discriminating music listeners. You are probably no
freshman when it comes to stereo. Never-the-less we ask you
to read and carefully follow these instructions to insure a
successful partnership between you and your new stereo
equipment.

You now have "THE BEST." Used properly you are in for
thousands of hours of musical enjoyment.

If you are in a hurry, read page 3 first. This gives you a brief
outline of what each control and indicator does. Reading time
for this manual is 30 minutes. This is time well spent.

MR 71 FM STEREO TUNER

INTRODUCTION

The Mclntosh MR 71 is a precision engi-

neered, highly sensitive FM Multiplex Tuner.

The research staff of Mclntosh Laboratory
has developed five new tuner circuit improve­ments for the MR 71.

1. Automatic stereo-mono switching that
is "clickless" and completely electronic.
(Patent applied for.)

2. Multipath indicator to eliminate multi-

path reception by showing when your anten-

na is rotated to the correct position for mini-

mum multipath distortion.

3. Double tuned input circuits before the
first R.F. amplifier to reduce spurious re­sponses.

4. New D'Arsonval movement meters of
increased sensitivity which do not need zero
setting adjustments.

5. A new computer designed filter to re­duce noise from stations broadcasting sub­carrier auxiliary music services. No other
tuner uses such a filter.

The MR 71 also uses the exclusive Mc­lntosh PANLOC method of 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 PANLOC but­tons on the front panel locks the tuner firmly
into place for normal operation. To unlock
the tuner depress the PANLOC buttons a
second time. The tuner can now slide from
the front panel. The tuner will lock into this
position, preventing accidental release of
the tuner from the installation. Depressing
the holding latches allows the tuner to be
taken out of the PANLOC shelf or to slide
back into position against the mounting panel.

The finest possible reception of FM mono-

phonic and FM multiplex stereophonic broad­casts is assured by the Mclntosh MR 71
tuner.

Once you have enjoyed the outstanding
performance of the MR 71, you will under­stand why Mclntosh products have earned

their reputation as "THE BEST." Your Mc-

lntosh MR 71 tuner will give you years of the
finest possible FM reception, and will be a

valued part of your home music system.

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TECHNICAL DESCRIPTION

The MR 71 tuner has a 6DS4 high-grain

Nuvistor for the first RF amplifier. The Nuvis­tor (triode) operates into a second triode tube
to form a cascade amplifier. Careful design
of the operating characteristics allows the
cascade amplifier to handle a wide dynamic

range of signals with excellent signal-to-

noise ratio.

A double-tuned RF input circuit combined

with the Nuvistor-tube cascade amplifier

reduces spurious signals to an extremely low

value. Sensitivity is increased to the highest

possible rating, while still retaining high

selectivity.

A newly developed Automatic Frequency
Control (AFC) circuit greatly simplifies tuning.
As the tuning knob is moved, the AFC circuit
automatically cuts off for sharpest tuning.
After the station is tuned in, the AFC circuit
gradually comes into operation over a 3

second interval. The AFC action automatically

brings the tuning to minimum distortion. This
automatic tuning repeats its action each
time the tuning dial is moved to a new sta­tion. The amount of AFC action is fully ad­justable with a front panel control.

The AFC circuit is unique. It uses a silicon
diode in place of a conventional tube. The
silicon diode improves the overall AFC per­formance. It is unaffected by temperature
changes. It has no warm-up drift and elimi-

nates the chance of tube filament hum. A
temperature-compensated narrow band de­tector supplies operating signals to the AFC
circuit. This insures positive AFC action. The

narrow band detector also operates the FM
tuning meter amplifier and the ultrasonic
muting circuit.

The Mclntosh developed ultrasonic muting
circuit automatically suppresses all intersta­tion noise, including the noises usually heard
tuning in and out of a station. Weak or distant
stations that can't override the background
noise and interference are suppressed by the
muting. A front panel switch allows muting to
be cut off for listening to weak and noisy
stations. A back panel adjust control is fac­tory set to the correct muting threshold level.

The mixer output is amplified through five

intermediate frequency stages with flat­topped highly selective response curves.
The IF transformers have wide band re­sponse with maximum adjacent channel

rejection. Construction of the IF transformers
assures electrical stability and resistance to
mechanical shock and vibration. More than
adequate gain is provided to operate both
limiters on the weakest signals. Two com­plete limiters are used for the best possible
signal-to-noise ratio.

A separate wide band detector handles
only audio frequencies for low distortion and
wide frequency response.

Both the RF and IF circuits are completely
shielded in excess of FCC requirements for
suppression of radiation of the FM oscillator
and IF frequencies.

The MR 71 multiplex decoder uses a
Mclntosh developed detector. The advantage
of this circuit is the elimination of critical
adjustments necessary with commonly used
multiplex matrixing methods. The L-R (left
minus right) stereo sidebands are detected.
Then automatically combined with the L+R
main carrier signal. The left and right chan­nel signals are then produced with excellent
separation.

A temperature stabilized 19KC amplifier
locks in a highly stable 38KC synchronous
oscillator. This method gives exceptional
noise immunity. Balanced detectors cancel
the 38KC signal components in the output,
providing low distortion and reduced sus­ceptibility to spurious signals. Tape record­ing interference is minimized by this method.

A highly selective computer designed filter
reduces noise from stations broadcasting
auxiliary music services. The filter reduces

the frequency band from 63-74KC approxi-

mately 50db. The filter response slope is
275db per octave. The noise is eliminated

without affecting normal program material.

The MR 71 has a multiplex stereo indicator

which lights when the dial pointer crosses a

station broadcasting multiplex stereo. A
unique circuit using a transistor operates the

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Your Mclntosh MR71 tuner will give you many years of pleasant
and satisfactory performance. If you have any questions concern­ing the operation or maintenance of this tuner please contact:

Customer Service

Mclntosh Laboratory Inc.

2 Chambers Street

Binghamton, New York
Our telephone number is 723-5491.
The direct dial area code is 607.

GUARANTEE

Mclntosh Laboratory Incorporated guar- period of 90 days from date of purchase,

antees this equipment to perform as adver- This guarantee does not extend to compo-

tised. We also guarantee the mechanical and nents damaged by improper use nor does it

electrical workmanship and components of extend to damage incurred during transpor-

this equipment to be free of defects for a tation to and from Mclntosh Laboratory, Inc.

3-YEAR FACTORY SERVICE CONTRACT

An application for a FREE 3-YEAR FAC- fined in the 3-year factory service contract.
TORY SERVICE CONTRACT is included in the If the application is not mailed to Mclntosh
pocket in the back cover of this manual. The Laboratory, only the services offered under
FREE 3-YEAR FACTORY SERVICE CONTRACT

the standard 90-day guarantee will apply on
will be issued by Mclntosh Laboratory upon this equipment. TAKE ADVANTAGE OF 3
receipt of the completely filed out applica- YEARS OF FREE FACTORY SERVICE BY

tion form. The term of this contract is de- FILLING IN THE APPLICATION NOW.

Design subject to change without notice.

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MPX stereo indicator lamp. The transistor is
controlled by a noise-rejecting differential
detecting bridge circuit. The circuit discrimi­nates between noise and the 19KC multiplex
pilot signal. The indicator will light only on

the 19KC signal present in a multiplex stereo

broadcast.

The MR 71 uses a new Mclntosh developed
automatic mono-stereo switching circuit.
(Pat. Pend.) The switching is electronic with­out switching clicks or transients.

The circuit switches smoothly and silently

when the 19KC multiplex carrier is present.

The multipath signal indicator on the tun­ing dial is an electron ray tube. This is an
exclusive Mclntosh development. Multipath
signal reception causes moderate to severe
distortion and poor stereo channel separa-

tion. By knowing the presence of multipath

reception, a directional FM antenna may be
rotated to reduce or eliminate the multipath

signal. The MR 71 multipath indicator shows

if there are multipath signals present by
rapid fluctuation of the electron ray beams.

With the antenna correctly positioned, the

indicator beams remain relatively steady,
showing that multipath distortion has been
eliminated.

Two pairs of audio output jacks are on the

back panel. One pair of jacks is controlled
only by the front panel volume control. The
other pair of jacks is controlled only by the
back panel output adjust controls. Two stage
feedback type preamplifiers on both chan-

nels provide low impedance outputs. More
than sufficient output volume is available to
feed power amplifiers as well as preamplifiers.

A new type of mechanical tuning assembly
gives the MR 71 extremely smooth flywheel
tuning action. The tuning capacitor is driven
directly, and in turn drives the pointer. Back-

lash is eliminated with this design. A teflon
lined pointer carriage and nylon pulleys re­duce friction and wear to give an unusually
smooth and quiet dial action.

IF YOU ARE IN A HURRY

Turn antenna so the eye is steady.

Adjust to desired volume.

Tune for Max. reading.

Power off. Use stereo-auto
position: will switch
automatically from stereo to mono.

Will light only on stations

broadcasting MPX stereo,

Tune for center of black area.

Continuously variable, use

Max. position for MPX reception.

Tuning . . . select

desired station

In ... eliminates interstation
noise. Out . . . use to receive
weak stations.

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