McIntosh MR 71, Руководство пользователя

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TECHNICAL DESCRIPTION
The MR 71 tuner has a 6DS4 high-grain
Nuvistor for the first RF amplifier. The Nuvis-
tor (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 sta-
tion. The amount of AFC action is fully ad-
justable 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 per-
formance. 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 de-
tector 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 intersta-
tion 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 fac-
tory set to the correct muting threshold level.
The mixer output is amplified through five
intermediate frequency stages with flat-
topped highly selective response curves.
The IF transformers have wide band re-
sponse 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 com-
plete 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 chan-
nel 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 sus-
ceptibility to spurious signals. Tape record-
ing 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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