McIntosh MR 65 Owners Manual

Page 1

Page 2

MR65 STEREO TUNER GENERAL DESCRIPTION Care, in the greatest degree has been devoted on this tuner during research, design, engineering, and manu- facture. So throughly has every detail of this equipment been planned and carried out that even its appearance speaks of the quality workmanship that is used through- out. Once you have learned to use the MR-65 . . . expe- rienced the operation of its controls and many functions . . . and had the opportunity to evaluate its performance . . . you will understand how effectively traditional Mcln- tosh design and engineering have been combined to defeat obsolescence and provide years of trouble-free performance. The MR-65 is highly flexible in its operation. It will receive either monophonic or stereophonic FM broad- casts. A front panel volume control and two-stage audio amplifier allow the MR-65 to operate through any type of monophonic or stereophonic equipment including pre- amplifiers, power amplifiers, tape recorders, etc. All provisions have been made to connect an adapter for any type of multiplex system the Federal Communica- tions Commission may adopt as a result of their present investigation and series of tests. Mclntosh will manu- facture a built-in multiplex adapter designed to fit in a prepared chassis opening. You can connect it with a minimum of effort. Or, if you choose, an external multi- plex adapter can be connected to the jack provided on the back panel. TECHNICAL DESCRIPTION The MR-65 RF tuning section uses a cascode ampli- fier, specially designed to amplify "weak signals" for less noise and distortion. Three flat-topped IF amplifiers reject adjacent channel interference. They give enough gain for weak signals to operate the limiters. Two cas- caded limiters further improve the signal-to-noise ratio. A 4-gang capacitor and an additional tuned circuit in- creases RF selectivity, reducing spurious or unwanted signals. The MR-65 uses two temperature compensated dis- criminators. One is a narrow-band discriminator used for ultrasonic muting, automatic frequency control, and tun- ing meter drive. The second one is a broad-band dis- criminator that gives nearly perfect audio performance. A variabie-capacitance silicon diode is used in the AFC circuit instead of a conventional tube. The silicon diode improves AFC action, is unaffected by temperature changes, eliminates filament hum, and does not drift during warm-up. The newly developed AFC circuit automatically aids tuning. During manual tuning, the MR-65 responds as if no AFC were operating. When manual tuning is com- pleted a small difference usually remains between the lowest distortion setting and the manual tuning setting. The new circuit brings the AFC into action gradually, over approximately a three second interval, to improve the tuning electrically and automatically. This automatic advantage is repeated each time a station is tuned on the MR-65. The AFC is completely variable by a control on the front panel. The excellent sound quality of the MR-65 is the result of using a two-stage, low impedance, feedback audio amplifier. A front panel volume control permits con- venient adjustment of output level. The RF and IF circuits of the MR-65 are completely shielded and exceed the FCC requirements for suppres- sion of oscillator radiation. Either a 300 ohm or 75 ohm antenna may be used with the MR-65. A VHF television antenna which is suitable for FM reception can be con- nected to the MR-65. When the tuner is turned off, it switches the antenna back to the TV receiver (see An- tenna Connecting Instructions). In the MR-65, a new type of mechanical tuning assembly gives smooth flywheel tuning. With direct drive to the tuning capacitor, which in turn drives the pointer, backlash is almost eliminated. For smooth, quiet action and extended life with virtually no wear, a teflon lined pointer carriage and nylon pulleys are used in the dial cord assembly. ELECTRICAL SPECIFICATIONS USABLE SENSITIVITY 3¼ microvolts at 100% modulation (± 75 kc.) for less than 3% total noise and distortion in accordance with IHFM Standards. AUDIO FREQUENCY RESPONSE Within 2 db from 20-20,000 cycles. DISTORTION Less than 3% for 100% modulation (accuracy of the best available test equipment is not guaranteed below 3%). CAPTURE RATIO 1 to 0.7. MUTING At least 60 db noise reduction between stations. OSCILLATOR DRIFT Less than 25 kc. with AFC disabled; negligible with AFC in operation. IMAGE REJECTION Better than 80 db at 90 mc.; better than 70 db at 105 mc. HUM Better than 65 db below 100% modulation. OUTPUT Approximately 4 volts; low impedance. ANTENNA INPUTS 300 ohms balanced; 75 ohms unbalanced. POWER CONSUMPTION 75 watts, 105 to 125 volts, 50-60 cycles. TUBE COMPLEMENT 6BN4A RF Amplifier 6SC6 2nd Limiter 6BN4A Oscillator 6BN8 Squelch amplifier and AGC Clamp 12AT7 Mixer 6C4 Meter (3) 6AU6 IF Amplifiers 6U8A Audio amplifier 6AU6 1st Limiter EZ80/6V4 Rectifier 1