MAINTENANCE MANUAL C20 STEREO PREAMPLIFIER (Serial No.
R5 R7 (2 used) C102 C103 C104 R1 R2 R3 R4 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 S1 S2 S3 S4 S5 S6 S7 S8 S9 S1, S2 M199A Switch, Input Selector Switch, Bass Compensator Switch, Treble Compensator Switch, High Frequency Cutoff Filte
Table 1. C20 VOLTAGE AND RESISTANCE CHART (Schematic No. SC117-201) Tube Pin No. 12AX7 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 0 1 2 3 4 (V1) 12AX7 (V2) 12AU7 (V3) 5 6 7 12AU7 (V4) 8 9 1 2 3 4 5 12AX7 (V5) 12AX7 (V6) 12AX7 (V7) 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 6X4 (V8) 5 6 7 8 9 1 2 3 4 5 6 7 DC Volts No. Signal Resistance in Ohms Unit Off 146 0 1.0 5.6 -5.6 110 0 1.0 130K* 1M 2.2K 5 5 360K* 56K 4K 146 0 1.0 5.6 -5.6 110 0 1,0 — 130K* 1M 2.
NOTES: THlS SCHEMATIC APPLIES TO C20 UNITS C104 FOR MMFD LOW NOISE OR A SPECIAL R E S I S T A N C E TAPER. * THESE COMPONENTS HAVE A CLOSE T O L E R A N C E ON THEIR VALUE, OR HAVE SPECIAL CHARACTERISTlC. CHARACTERISTICS SUCH AS TRACKING FOR NUMBERS GREATER THAN ONE. CONTROLS CONDENSERS. ONE, AND IN MFD/15V THAN EXCEPT AS NOTED. NUMBERS L E S S ½WATT POSITION.
Your C20 will give you many years of pleasant and satisfactory performance. If you have any questions concerning the operation or maintenance of this pre-amplifier please contact: Customer Service Mclntosh Laboratory Inc. 2 Chambers Street Binghamton, New York Our telephone number is 723-5491. The direct dial area code is 607. LABORATORY INC. 2 CHAMBERS STREET, BINGHAMTON, N. Y.
