McIntosh C22 Vintage Tube Preamplifier, Restored, Highly Collectable
This is the Holy Grail of preamps from McIntosh.
An All-Tube unit providing that warm and engaging vintage sound that so many are after.
This C22 underwent an in-house SkyFi preservative restoration. This example came to us as a very good restoration candidate: In all-original condition, a full compliment of Telefunken output tubes, and featuring Sprague Di-Film coupling capacitors throughout rather than the typical bumble bee paper caps that we are used to seeing in these units.
Our preservative restoration started with a full rebuild of the power supply. This involved replacing all of the aging multi-section capacitors with modern reproductions, all new rectifier diodes, and all new resistors (replaced with period correct NOS and modern production Carbon Composition parts where applicable). The two axial electrolytic capacitors on the main board were also replaced. At this point the unit was stable and ready for initial testing. The power supply voltages were all within the expected range and the unit passed all of our standard bench tests.
We prefer to stop the restoration at this point instead of bulk replacing the coupling capacitors in an effort to maintain the original sonic character of the piece. We did spot check select Di-Film capacitors for value and leakage. All of the carbon comp resistors were checked for drift and tolerance from the right to left channels.
Each and every tube was tested on our modern and professional Amplitrex AT1000 with great results. It's clear that this preamp saw relatively light use throughout its lifetime. All (6) tubes are Telefunken Long Smooth Plate, a set valued at $500-600 alone.
Our restoration concluded with a thorough cleaning and detailing of the glass, knobs, chassis, and jacks.
±0.5 db from 20 cps to 20,000 cps.
Less than 0.2% at 10 volts output, 20 to 20,000 cycles. Less than .02% at 3 volts output, 20 to 20,000 cycles.
HUM AND NOISE
High Level Inputs: 85 db below rated output
Low Level Inputs: Less than 1.5 microvolts at input terminals.
INPUT SENSITIVITY AND IMPEDANCE
Auxiliary, Tape, Tuner 1, and Tuner 2: 0.25 volts, 250,000 ohms. Phono 1 and Phono 2: 2 millivolts, 47,000 ohms. Microphone: 2.5 millivolts, 1 megohm.
Tape Head: 2 millivolts, 1 megohm.
Tape Compare: 0.25 volts, 250,000 ohms.
Main (2 jacks on each channel) : 2.5 V with rated output. Tape: 0.25 V with rated output. Left Plus Right: 1 V from generator impedance of 25,000 ohms.
Auxiliary, Tape, Tuner I, and Tuner 2: To Main Output, 20 db (10 to 1).
To Tape Output, 0 db (1 to 1). Phono 1 and Phono 2 (At 1 KC): To Main Output, 62 db (1250 to 1). To Tape Output, 42 db (125 to 1). Microphone: To Main Output, 60 db (1000 to 1). To Tape Output, 40 db (100 to 1). Tape Head (At 500 cps): To Main Output, 62 db (1250 to 1). To Tape Output, 42 db (125 to 1).
AUXILIARY AC OUTLETS (5)
1 unswitched for turntable or tape machine (Red), 4 switched (Black).
117 volts 50/60 cps AC, 34 watts.
6 each 12AX7.
TAPE JACK SWITCH
2 position, connects panel jacks to allow signals to be fed from or to the C22 to record or playback using an external portable tape recorder.
Separate channel 11 position switch type,± 20db at 20 cycles.
Separate channel 11 position switch type,±20 db at 20,000 cycles.
COMPENSATOR SWITCH RIAA or LP record equalization.
TAPE SWITCH Normal, or Tape Monitor.
RUMBLE FILTER 50 cps cutoff.
HF FILTER 5000 cycle cutoff.
ADDITIONAL SET·UP CONTROLS
The following controls are located behind the front panel on the top of the C22 chassis. These controls are readily accessible by depressing the PANLOC buttons to slide the C22 forward from the mounting panel.
OUTPUT LEVEL CONTROLS (L, L+ R, AND R)
Allows the balance of the enti re system to be conveniently adjusted.
LOW FREQUENCY TRIM CONTROLS (L AND R)
Allows frequencies below 100 cps to be boosted up to 6 db
TAPE EQUALIZATION CONTROLS (L AND R) Adjusts tape head input high frequency response.
2 position, normal (0°) or reverse (180°).
PILOT LAMP INTENSITY SWITCH 2 position, bright or dim.
Front panel; 16 inches wide by 57/16inches high; chassis (including PANLOC shelf) 15 inches wide by 5 inches high by 13 inches deep, including connectors; clearance in front of mounting panel including knobs,lYz inches.
16 pounds net, 25 pounds in shipping carton.
The SkyFi Testing Process for Preamplifiers:
We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and transistors are checked for signs of stress or damage. Special attention is paid to the power supply which is the most common source of failure for preamps. We then power up the unit and run a simple 1k sine wave while monitoring the low voltage output on an oscilloscope for signs of distortion or noise to get a baseline.
At this point we will lubricate and clean all switches and potentiometers (that are not sealed) with a high quality contact cleaner, and then re-test all functions for any signs of noise or scratching.
Final testing involves putting actual music through the preamplifier We have learned over time that some issues are only noticeable to a trained ear while listening to a familiar source material. Our test bench has reference vintage KEF speakers that we are super familiar with which will quickly reveal any discrepancies. Some preamps will then move into the listening room where they will be tested with our in-house reference system.
Please click here for detailed specifics regarding our specialized packing process that separates us from the rest.
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