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MC 250 SERVICE INFORMATION S T A R T I N G WITH S E R I A L N O . 23L48 MCINTOSH LABORATORY INC. 2 CHAMBERS STREET BINGHAMTON, NEW YORK MC 250 ELECTRICAL SPECIFICATIONS Power Output: 100 watts RMS continuous, 50 watts per channel operating simultaneously, into 4 ohm, 8 ohm, or 16 ohm loads. Harmonic Distortion: Less than 0.25% at rated power output from 20Hz to 20,000Hz. Intermodulation Distortion: Less than 0.25% for any combination of frequencies between 20 Hz and 20,000 Hz. Frequency Range: At rated output both channels: through 20,000Hz. Output Damping Factor: Greater than 10 for any output tap. Input Sensitivity & Impedance: Input sensitivity is 0.5 volts. Hum & Noise : Greater than 90dB below rated output. Power Requirements: 117 volts AC,50-60Hz, 50 watts at zero signal output, 250 watts at rated output. Input impedance Is 200K ohms. +0 to -0.25dB from 20Hz MC 250 MC 250 LEFT CHANNEL POWER OUTPUT PRINTED CIRCUIT BOARD 043-916 RIGHT CHANNEL POWER OUTPUT PRINTED CIRCUIT BOARD 043-916 INPUT SECTION PRINTED CIRCUIT BOARD 043-795 MC 250 MC 250 MC 250 SCHEMATIC NOTES 1. Unless otherwise s p e c i f i e d : R e s i s t a n c e v a l u e s are i n ohms, 1 / 2 w a t t , and 10% t o l e r a n c e ; c a p a c i t a n c e v a l u e s s m a l l e r than 1 are i n m i c r o f a r a d s ( µ F ) ; c a p a c i t a n c e v a l u e s g r e a t e r than 1 a r e i n p i c o f a r a d s ( p F ) ; i n d u c t o r s are i n mi c rohen r i es ( µ H ) . P r i n t e d c i r c u i t board components are o u t l i n e d o n t h e s c h e m a t i c s b y dotted lines. The c i r c l e d numbers on the d o t t e d l i n e s c o r r e s p o n d to the numbers on the PC Board l a y o u t s . The heavy l i n e s on the s c h e m a t i c s denote the p r i m a r y s i g n a l A l l voltages conditions : a. b. c. d. e. path. 2. 3. 4. i n d i c a t e d o n the s c h e m a t i c s a r e measured under the f o l l o w i n g megohm impedance V T V M . Use of an 11 A l l v o l t a g e s ± 1 0 % w i t h r e s p e c t t o c h a s s i s ground. No s i g n a l at input t e r m i n a l s . A C input a t 1 1 7 v o l t s , 50/60Hz. Front panel Left Gain Right Gain Mode controls at: F u l l y CCW F u l l y CCW Stereo 5. 6. I n u n i t s w i t h S e r i a l N o . ' s b e l o w 2 8 L 2 1 : R88, R89, R90 & R 9 1 are used; R49 & R50 are 2200W; R86 & R87 are 160W; and R 3 3 & R34 are 3 3 k . I n u n i t s w i t h S e r i a l N o . ' s from 28L60 t o 3 7 L 7 5 , C 5 & C 6 a r e 180pF. Q21 BOTTOM Q25 TOP Q19 BOTTOM Q23 TOP Q26 TOP Q22 BOTTOM Q24 TOP Q20 BOTTOM L O C A T I O N O F T R A N S I S T O R S NOT O N P R I N T E D C I R C U I T B O A R D S MC 250 R E P L A C E M E N T PARTS All parts not listed are common items o b t a i n able from radio parts jobbers . Rep1acement parts may be o b t a i n e d when ordered by PART NUMBER from: Mclntosh Laboratory Inc. Customer Service Department 2 Chambers Street Binghamton, New York 13903 (telephone 607 723-3512)