Back Panel Information
TP1 and TP2
Test points TP1 and TP2 are used with the Mclntosh
Maximum Performance Indicator.
120 V AC POWER OUTLET
Provides 120 volt AC power up to 400 watts for addi-
tional equipment such as amplifiers, etc. This outlet
is not fused. It turns on and off with the front panel AC
power switch on the VOLUME control.
AC POWER CORD
Connect the AC power cord to a 120 volt, 50 to 60
Hz power line receptacle. The power used by the
MR 78 is 35 watts.
FUSE
A 0.5 AMP fuse protects the tuner circuits. This fuse
does not protect additional equipment connected to
the back panel AC power outlet.
ANTENNA CONNECTION STRIP
Provides easy push type connectors for 300 ohm FM
antenna and a ground connection.
FM ANTENNA -75 OHM
Provides a "type F" connector for a 75 ohm unbal-
anced FM antenna.
AUDIO OUTPUTS
The left-hand pair of AUDIO OUTPUT jacks pro-
vides FIXED OUTPUT audio signals. The program at
these jacks is not affected by the MR 78 front panel
VOLUME control. Use these output jacks to connect
the tuner to a stereo control preamplifier or other
equipment which has its own volume control.
The right hand pair of AUDIO OUTPUT jacks pro-
vides a FRONT PANEL CONTROLLED audio signal.
The program at these jacks is controlled by the MR 78
front panel VOLUME control. Use these output jacks
to connect to external power amplifier, tape recorders,
or any equipment where continuous front panel con-
trol of tuner output volume is desirable.
Front Panel Information
The MR 78 Tuner has the most flexible control sys-
tem ever designed in a stereo FM tuner. Use of these
controls will give you a higher level of performance.
VOLUME CONTROL AND AC POWER SWITCH
The VOLUME control has been precision tracked
throughout the listening range (0 to -65 dB) for accu-
rate stereo balance.
It sets the output level of the tuner FRONT PANEL
CONTROLLED AUDIO OUTPUT jacks. The FIXED
OUTPUT jacks are not affected by the VOLUME con-
trol.
The AC power switch is part of the VOLUME control.
Turning the volume control fully counterclockwise
turns the AC power off.
TUNING DIAL AND METER
The MR 78 has two dial scales:
1. FM scale - marked 88 to 108 MHz
2. 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.
A small portion of the dial pointer has been illuminated
to increase the ease of tuning. An FM station is tuned
correctly when the TUNING meter pointer is in the
black area of the meter scale. The tuning indication is
independent of the station signal strength. Maximum
left and right pointer swing, which occurs as you tune
through a station, is dependent on the setting of the
SELECTIVITY switch.
STEREO FUNCTION INDICATOR
The STEREO FUNCTION indicator lights red when
the dial pointer is tuned to or crosses a station broad-
casting the 19,000 Hz pilot signal for stereo. The special
circuit used will light only when the 19,000 Hz multi-
plex pilot is present. The indicator will not light on
noise pulses or interference. The STEREO FUNCTION
indicator will light regardless of the MODE switch
setting.
MODE SWITCH
The MODE switch has three settings.
STEREO ONLY - Only stations broadcasting the
19,000 Hz pilot signal for stereo can be heard in this
position. All monophonic stations and background
noises are suppressed. The TUNING meter and SIGNAL
STRENGTH meter function will indicate monophonic
broadcasts when tuning but no program will be heard
from the loudspeakers.
MONO-In this position of the MODE switch, all broad-
casts will be heard monophonically. The automatic
stereo switching is bypassed. The STEREO FUNCTION
indicator will light when a station is transmitting
stereo, but the program heard from the loudspeakers
will be mono.
STEREO AUTO - In this position of the MODE switch
both mono and stereo broadcasts are heard. The tuner
automatically switches from mono to stereo mode of
operation, depending on the type of broadcast being
received.
MUTING SWITCH AND FUNCTION INDICATOR
Muting suppresses the background noise and hiss
normally heard between stations. Turn the control
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