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Multiplex Output
The output on the back of the MR-55 marked "MULTIPLEX OUTPUT" is an unfiltered output for
feeding a multiplex adapter.
The selector switch is a six position switch that has the following identifications: ( 1 ) F. M. LISTEN,
(2) F. M. TUNE, (3) A. M. BRD. (4) A. M. MED., (5) A. M. SHARP, (6) PHONO.
Phono
The input sensitivity is 0.25 volts, suitable for a crystal or ceramic type phono cartridge, a magnetic cart-
ridge with a one tube preamplifier, or the output of a tape recorder.
A. M. Sharp
The audio response of this position is limited to 20 cycles to 2000 cycles. In the "A. M. SHARP" position
distant stations can be received with maximum clarity and minimum noise. Tune to a peak on the signal
strength or right meter. The left meter or center of channel meter is only in use on F. M.
A. M. Med.
The audio response of the A. M. MED. position is limited to 20 cycles to 6500 cycles. This position is
less selective on noise than the "SHARP" position.
A. M. Brd.
The unrestricted audio response is 20 to 10,000 cycles for maximum A. M. fidelity on strong local sta-
tions where noise is not a problem. Tune to a dip between two peaks on the signal strength meter, or the
loudest sound.
Whistle Filter
In all A. M. positions there is a 70 DB rejection of the 10 K.C whistle.
F. M. Tune
Automatic frequency control (A. F. C.) is disabled and ULTRASONIC MUTING is added for maxi-
mum accuracy and ease in tuning. Ultrasonic muting eliminates the annoying noise between stations. In tun-
ing across the band take notice of the complete absence of noise even when approaching a station.
Some stations are received with insufficient signal strength to completely eliminate background "noise. The
ultrasonic muting circuit has been so designed to permit only listenable signals through. Signals with annoy-
ing background noise will be muted. The meters will function normally and indicate the presence of a sta-
tion. If a desired station is not heard, tune by meter and change the selector switch to "F. M. LISTEN." The
station can then be heard. Ultrasonic muting is an exclusive Mclntosh development and feature.
If an antenna with a rotor is used the signal strength meter can be of assistance in determining the
proper direction to point the antenna. Rotate the antenna until maximum signal strength is registered on the
meter. The best signal to noise ratio usually will result at highest indicated signal strength.
F. M. Listen
The ultrasonic muting circuit is defeated and A. F. C. added for greatest listening pleasure. Mclntosh
A. F. C. does not change in any respect the low distortion characteristics of the MR-55.
Volume
The volume control has at its extreme counter-clockwise rotation the A. C. on-off switch. The switch
also controls the A. C. available at the auxiliary A. C. outlet on the back of the tuner. Normal operation for
the "VOLUME" control is totally clockwise.
A. M. Sensitivity
The A. M. sensitivity is the greatest at the clockwise position of the switch, the center position is inter-
mediate sensitivity, and the counter-clockwise position is minimum sensitivity.
The clockwise or maximum sensitivity position will deliver the greatest number of stations. Long distant
reception will be best in this position. When selecting local stations between station noise can be reduced by
using either the minimum or intermediate sensitivity positions which ever is most satisfactory for your location.
OPERATION
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