McIntosh C20 Service Manual
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Extracted text from McIntosh C20 Service Manual (Ocr-read)
Page 1
DESCRIPTION COMPONENT NO. Switch, Input Selector Switch, Bass Compensator Switch, Treble Compensator Switch, High Frequency Cutoff Filter Switch, Rumble Filter Switch, Mode Selector Switch, Tape Compare Switch, Tape Jack Switch, Phase Silicon Rectifier, 50 PIV at 1.6A Transformer, Power S1 S2 S3 S4 S5 S6 S7 S8 S9 S1, S2 M199A DESCRIPTION COMPONENT NO. Filter Capacitor, 20/20/40 MF at 300/350/350V Filter Capacitor, 40/40 MF at 350/350V Filter Capacitor, 1000/1000 MF at 15/15V Control, Bass Control, Treble Control, Loudness (Aural Compensator) Control, Volume - 4 Section combined with power on-off switch Control, Balance Control, Bass Trim (Lo Bass) on rear panel C102 C103 C104 R1 R2 R 3 R4 R5 R7 (2 used) Special components used in the C20 are listed below. These compo- nents are designed and built specifically for the C20. They may be pur- chased directly from Customer Service, Mclntosh Laboratory Inc. When you Table 2. SPECIAL COMPONENTS (Schematic No. SC119-201) order parts be sure to give the SCHEMATIC NO. and DESCRIPTION from Table 2 below, and serial and model number for your amplifier.
Page 2
Table 1. C20 VOLTAGE AND RESISTANCE CHART (Schematic No. SC117-201) Tube 12AX7 (V1) 12AX7 (V2) 12AU7 (V3) 12AU7 (V4) 12AX7 (V5) 12AX7 (V6) 12AX7 (V7) 6X4 (V8) Pin No. 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 DC Volts No. Signal 146 0 1.0 5.6 -5.6 110 0 1.0 - 146 0 1.0 5.6 -5.6 110 0 1,0 64 0 2.4 5.6 -5.6 198 62 120 - 64 0 2.4 5,6 -5.6 198 62 120 - 104 0 .7 5.6 -5.6 230 22 29 _ 104 0 .7 5.6 -5.6 200 22 29 - 250 20 70 5.6 -5.6 250 20 70 0 315 AC - 6.3 AC 0 __ 315 AC 335 Resistance in Ohms Unit Off 130K* 1M 2.2K 5 5 360K* 56K 4K - 130K* 1M 2.2K 5 5 360K* 56K 4K _ 120K* <50 1.8K 5 5 14K* 1.1M 100K - 120K* <50 1.8K 5 5 14K* MM 100K - 330K* 110K 1.8K 5 5 9K 222K 22K - 330K* 110K 1.8K 5 5 31K* 222K 22K - 7K* 1M 47K 5 5 7K* 1M 47K 0 580 _ .1 0 - 560 * NOTES: 1. High impedance VTVM is used to measure operating voltages. 2. Resistance measured to grid, (chassis) 3. * Denotes pin 7 of V8 grounded for this test. 4. Control positions for tests are as follows; MODE SELECTOR BALANCE PHASE H.F. FILTER LOUDNESS INPUT SELECTOR BASS COMPENSATOR TREBLE COMPENSATOR BASS TREBLE RUMBLE FILTER, TAPE JACK, TAPE COMPARE VOLUME LOW FREQUENCY TRIM STEREO 0 0 FLAT FLAT TAPE HD 2 0 TAPE 0 0 OUT ON, CCW 0