McIntosh MR 65B Owners Manual
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Extracted text from McIntosh MR 65B Owners Manual (Ocr-read)
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MR65B FM STEREO TUNER INTRODUCTION The Mclntosh Model MR65B is a precision- engineered, sensitive FM multiplex stereo tuner. It offers the finest possible reception of FM monophonic and FM multiplex stereo- phonic broadcasts. Every desirable feature for your FM listening pleasure is included in the MR65B tuner. It is perfect for use in a stereo music system where nothing less than "THE Best" will do. Once you have enjoyed the outstanding performance of the MR65B, you will under- stand why Mclntosh products have earned their reputation as "THE Best." Your Mclntosh MR65B tuner will give you years of the finest possible FM reception, and will become a highly valued part of your home music system. TECHNICAL DESCRIPTION The MR65B tuner has a 6DS4 high-gain Nuvistor for the first RF amplifier. The Nuvis- tor (triode) operates into a triode tube to form a cascode amplifier. Careful design of the operating characteristics allows the cascode 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 cascode 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 sec- ond interval. The AFC action automatically brings the electrical tuning to the correct point for minimum distortion. This auto- matic tuning repeats its action each time the tuning dial is moved to a different station. The amount of AFC action is fully adjustable with a front panel control. The AFC circuit is quite unique. It uses a silicon diode in place of a conventional tube. The silicon diode improves the overall AFC performance since it is unaffected by tem- perature changes, has no warm-up drift and eliminates the chance of tube filament hum. A special 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 ultrasonicmuting circuit automatically suppresses all inter- station noise, including the noises usually heard tuning in and out of a station. Weak or distant stations that don't over-ride the back- ground noise and interference are also sup- pressed by the muting. A switch on the front panel allows muting to be cut off for listening to these weak and noisy stations. A back panel adjust control is factory-set to the proper muting threshold level. Three flat-topped response IF amplifiers reject adjacent channel interference. More than adequate gain is provided to operate both limiters on the weakest signals. Two complete limiters are used to insure the best possible signal-to-noise ratio. A separate wide band detector handles exclusively the audio frequencies for low dis- tortion and wide frequency response. Both the RF and IF circuits are com- pletely shielded and exceed the FCC require- ments for suppression of radiation from the FM oscillator and IF frequencies. A unique multiplex stereo (MPX) indicator light is included on the front dial panel. The MPX indicator lights whenever the dial pointer crosses a station broadcasting FM multiplex stereo. The indicator uses a special noise-rejecting bridge circuit with two ger- manium diodes. The indicator lights ONLY on the 19KC carrier present in a multiplex stereo broadcast. It will not light on noise or inter- ference signals. The MR65B multiplex decoder circuit uses a special peak-switching, self-matrixing detector. Stereo channel separation is main- tained at better than 30db. 1
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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 MR65B an extremely smooth fly- wheel tuning action. The tuning capacitor is driven directly, and in turn drives the pointer. Backlash is practically eliminated with this method of design. A teflon lined pointer carriage and nylon pulleys reduce friction and wear to give an unusually smooth and quiet dial action. SPECIFICATIONS Useable Sensitivity 2.5 microvolts at 100% modulation (±75KC deviation) for less than 3% total noise and harmonic distortion in accordance with IHFM standards. Audio Frequency Response Within ½db from 20 to 20,000 cycles. Distortion Less than 0.5% at 100% modulation ±75KC deviation. Capture Ratio 1.5db at 100% modulation. Muting IF injected ultrasonic muting: at least 60db noise reduction between stations. Oscillator Drift Less than 25KC with AFC disabled; negligible with AFC in operation. Image Rejection Better than 80db at 90MC; better than 70db at 105MC. Hum Better than 70db below 100% modulation. Output Approximately 2.5 volts; low impedance. Antenna Inputs 300 ohms balanced; 75 ohms unbalanced. RF Amplifier Cascode with 6DS4 Nuvistor in first stage. IF Amplifiers Four, with 200KC bandwidth, flat top response Limiters Two Radiation Substantially below FCC requirements. Multiplex Channel Separation Better than 30db at 1000 cycles. Multiplex Filter Greater than 48db suppression of 19KC pilot and 38KC carrier. Multiplex Indicator Front panel multiplex stereo light activated by 19KC carrier-only. Multiplex Type Peak-detecting, self-matrixing detector. Tube and Semiconductor Complement 1-6DS4 Nuvistor, 1st RF. 1-12AT7, 2nd RF and Mixer. 1-6BN4A, Oscillator. 1-6AU6, 1st IF. 1-6AU6, 2nd IF. 1-6AU6, 3rd IF. 1-6AU6, 4th IF and 1st Limiter. 1-6CS6, 2nd Limiter and Muting. 1-6BN8, Muting Amplifier, Muting Detector, AVC Clamper. 2-6BL8, Left and Right, 1st and 2nd Audio Amplifiers. 1-12AU7, Balanced Tuning Meter Amplifier. 1-6U8, MPX Amplifier, MPX Indicator Con- trol. 2